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Atmospheric Modeling Division Publications: 2007

This page lists publication titles, citations and abstracts produced by NERL's Atmospheric Modeling Division for the year 2007, organized by Publication Type. Your search has returned 45 Matching Entries.

See also Atmospheric Modeling Division citations with abstracts: 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008

Technical Information Manager: Liz Hope - (919) 541-2785 or hope.elizabeth@epa.gov

		Presented/Published
JOURNAL	Daily Simulation of Ozone and Fine Particulates Over New York State: Findings and Challenges	07/01/2007

HOGREFE, C., W. HAO, K. CIVEROLO, J. Y. KU, G. SISTLA, R. S. GAZA, L. SEDEFIAN, K. L. SCHERE, A. GILLILAND, AND R. MATHUR. Daily Simulation of Ozone and Fine Particulates Over New York State: Findings and Challenges. JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY. American Meteorological Society, Boston, MA, 46(7):961-979, (2007).
Abstract:	This study investigates the potential utility of the application of a photochemical modeling system in providing simultaneous forecasts of ozone (O₃) and fine particulate matter (PM_2.5) over New York State. To this end, daily simulations from the Community Multiscale Air Quality (CMAQ) model for three extended time periods during 2004 and 2005 have been performed and predictions were compared to observations of ozone and total and speciated PM_2.5. Model performance for 8-hr daily maximum O₃ was found to be similar to other forecasting systems and to be better than that for 24-hr average total PM_2.5. Both pollutants exhibited no seasonal differences in model performance. CMAQ simulations successfully captured the urban/rural and seasonal differences evident in observed total and speciated PM_2.5 concentrations. However, total PM_2.5 mass was strongly overestimated in the New York City metropolitan area, and further analysis of speciated observations and model predictions showed that most of this overprediction stems from organic aerosols and crustal material. An analysis of hourly speciated data measured in Bronx County, New York, suggests that a combination of uncertainties in vertical mixing, magnitude and temporal allocation of emissions, and deposition processes are all possible contributors to this overprediction in the complex urban area.

JOURNAL	Sand Flux Simulations at a Small Scale Over a Heterogeneous Mesquite Area of the Northern Chihuahuan Desert	09/01/2007

BOWKER, G. E., D. GILLETTE, G. BERGAMETTI, B. MATICORENA, AND D. HEIST. Sand Flux Simulations at a Small Scale Over a Heterogeneous Mesquite Area of the Northern Chihuahuan Desert. JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY. American Meteorological Society, Boston, MA, 46(9):1410-1422, (2007).
Abstract:	Within areas of the Chihuahuan Desert dominated by honey mesquite bushes (Prosopis glandulosa), soil erosion causes open eroded patches and the formation of large coppice dunes. The airflow patterns around dunes and through the open areas are correlated with sand flux and erosion. This study uses wind velocity simulations from the Quick Urban & Industrial Complex (QUIC) model in combination with a sand flux parameterization to predict sand fluxes for each of eight storms occurring in the springs of 2003 and 2004. Total sand fluxes based on the sum of all the sand collectors located within the study domain were usually within 50% of the measured values for each of the storms, with predictions for individual sand collectors also often with 50% of the measured values. Predicted fluxes based on two different sand flux parameterizations were generally within 10% of each other, differing substantially only when the sand flux was low (near the threshold velocity). Good agreement between the field observations with a Sensit® instrument and QUIC predictions for the same location and time series suggests that QUIC could be used to predict the spatial and temporal variation of sand flux patterns for a domain.

JOURNAL	Refining Fire Emissions for Air Quality Modeling With Remotely-Sensed Fire Counts: A Wildfire Case Study	01/01/2007

ROY, B., G. POULIOT, A. GILLILAND, T. E. PIERCE, S. HOWARD, P. BHAVE, AND W. G. BENJEY. Refining Fire Emissions for Air Quality Modeling With Remotely-Sensed Fire Counts: A Wildfire Case Study. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(3):655-665, (2007).
Abstract:	This paper examines the use of Moderate Resolution Imaging Spectroradiometer (MODIS) observed active fire data (pixel counts) to refine the National Emissions Inventory (NEI) fire emission estimates for major wildfire events. This study was motivated by the extremely limited information available for many years of the United States Environmental Protection Agency (U.S. EPA) NEI about the specific location and timing of major fire events.

JOURNAL	A Statistical Approach for Estimating Uncertainty in Dispersion Modeling: An Example of Application in the Southwestern U.S.	01/01/2007

KORACIN, D., A. PANORSKA, V. ISAKOV, J. S. TOUMA, AND J. SWALL. A Statistical Approach for Estimating Uncertainty in Dispersion Modeling: An Example of Application in the Southwestern U.S. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(3):617-628, (2007).
Abstract:	This paper presents a new method based on a statistical approach of estimating the uncertainty in simulating the transport and dispersion of atmospheric pollutants. The application of the method has been demonstrated by using observations and modeling results from a tracer experiment in the complex terrain of the southwestern US.

JOURNAL	Receptor Modeling of Ambient Particulate Matter Data Using Positive Matrix Factorization Review of Existing Methods	02/01/2007

REFF, A. H., S. I. EBERLY, AND P. BHAVE. Receptor Modeling of Ambient Particulate Matter Data Using Positive Matrix Factorization Review of Existing Methods. JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION. Air & Waste Management Association, Pittsburgh, PA, 57(2):146-154, (2007).
Abstract:	Methods for apportioning sources of ambient particulate matter (PM) using the positive matrix factorization (PMF) algorithm are reviewed. Numerous procedural decisions must be made and algorithmic parameters selected when analyzing PM data with PMF. However, few publications document enough of these details for readers to evaluate, reproduce, or compare results between different studies. For example, few studies document why some species were used and others not used in the modeling, how the number of factors was selected, or how much uncertainty exists in the solutions. More thorough documentation will aid the development of standard protocols for analyzing PM data with PMF, and will reveal more clearly where research is needed to help future analysts select from the various possible procedures and parameters available in PMF. For example, research likely is needed to determine optimal approaches for handling data below detection limits, ways to apportion PM mass among sources identified by PMF, and to estimate uncertainties in the solution. The review closes with recommendations for documenting the methodological details of future PMF analyses.

JOURNAL	Using Cmaq for Exposure Modeling and Characterizing the Sub-Grid Variability for Exposure Estimates	09/01/2007

ISAKOV, V., J. IRWIN, AND J. K. CHING. Using Cmaq for Exposure Modeling and Characterizing the Sub-Grid Variability for Exposure Estimates. JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY. American Meteorological Society, Boston, MA, 46(9):1354-1371, (2007).
Abstract:	Atmospheric processes and the associated transport and dispersion of atmospheric pollutants are known to be highly variable in time and space. Current air quality models that characterize atmospheric chemistry effects, e.g. the Community Multi-scale Air Quality (CMAQ), provide volume-average concentration values for each grid cell in the modeling domain given stated conditions. Given the assumptions made and the limited set of processes included in any model's implementation, there are many sources of "uresolved" sub-grid variability. This raises the question of the importance of the "unresolved" sub-grid variations on exposure assessment results if such models were to be used to assess air toxic exposures. In this study, we applied the Hazardous Air Pollutant Exposure Model (HAPEM) to estimate benzene and formaldehyde inhalation exposures using ambient annual average concentrations predicted by CMAQ to investigate how within-grid variability can affect exposure estimates. An urban plume dispersion model was used to estimate the sub-grid variability of annual average benzene concentration values within CMAQ grid cells for a modeling domain centered on Philadelphia, PA. Significant (greater than a factor of two) increases in maximum exposure impacts were seen in the exposure estimates in comparison to exposure estimates generating using CMAQ grid-average concentration values. These results consider only one source of sub-grid variability, namely the discrete location and distribution of emissions, but they do suggest the importance and value of developing improved characterizations of sub-grid concentration variability for use in air toxic exposure assessments.

JOURNAL	Interannual Variation in Meteorologically Adjusted Ozone Levels in the Eastern United States: A Comparison of Two Approached	02/01/2007

ZHENG, J., J. SWALL, W. M. COX, AND J. M. DAVIS. Interannual Variation in Meteorologically Adjusted Ozone Levels in the Eastern United States: A Comparison of Two Approached. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(4):705-716, (2007).
Abstract:	Assessing the influence of abatement efforts and other human activities on ozone levels is complicated by the atmosphere's changeable nature. Two statistical methods, the dynamic linear model(DLM) and the generalized additive model (GAM), are used to estimate ozone trends in the eastern United States and to adjust for meteorological effects. The techniques and resulting estimates are compared and contrasted for four monitoring locations chosen through principal components analysis to represent regional patterns of ozone concentrations. After adjustment for meteorological influence, overall downward trends are evident at all four locations from 1997 through 2004. The results indicate that the two methods' estimates of ozone changes agree well. When such estimates are needed quickly, or when many similar, but separate analyses are required, the ease of implementation and relative simplicity of the GAMs are attractive. The DLMs are much more flexible, readily addressing such issues as autocorrelation, the presence of missing values, and estimation of long-term trends or cyclical patterns. Implementation of DLMs, however, is typically more difficult, and especially in the absence of an experienced practitioner, they may be better reserved for in-depth analyses.

JOURNAL	Evaluating the Use of Outputs from Comprehensive Meteorological Models in Air Quality Modeling Applications	03/01/2007

ISAKOV, V., A. VENKATRAM, J. TOUMA, D. KORACIN, AND T. L. OTTE. Evaluating the Use of Outputs from Comprehensive Meteorological Models in Air Quality Modeling Applications. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(8):1689-1705, (2007).
Abstract:	Currently used dispersion models, such as the AMS/EPA Regulatory Model (AERMOD), process routinely available meteorological observations to construct model inputs. Thus, model estimates of concentrations depend on the availability and quality of Meteorological observations, as well as the specification of surface characteristics at the observing site. We can be less reliant on these meteorological observations by using outputs from prognostic models, which are routinely run by the National Oceanic and Atmospheric Administration (NOAA). The forecast fields are available daily over a grid system that covers all of the United States. These model outputs can be readily accessed and used for dispersion applications to construct model inputs with little processing. This study examines the usefulness of these outputs through the relative performance of a dispersion model that has input requirements similar to those of AERMOD. The dispersion model was used to simulate observed tracer concentrations from a Tracer Field Study conducted in Wilmington, California in 2004 using four different sources of inputs: 1) onsite measurements; 2) National Weather Service measurements from a nearby airport; 3) readily available forecast model outputs from the Eta Model; and 4) readily available and more spatially resolved forecast model outputs from the MM5 prognostic model. The comparison of the results from these simulations indicate that comprehensive models, such as MM5 and Eta, have the potential of providing adequate meteorological inputs for currently used short-range dispersion models such as AERMOD.

JOURNAL	Electrostatic Forces in Wind-Pollination: Part 2: Simulations of Pollen Capture	03/01/2007

BOWKER, G. E. AND H. C. CRENSHAW. Electrostatic Forces in Wind-Pollination: Part 2: Simulations of Pollen Capture. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(8):1596-1603, (2007).
Abstract:	During fair-weather conditions, a 100 V m^-1 electric field exists between positive charge suspended in the air and negative charge distributed on the surfaces of plants and on the ground. The fields surrounding plants are highly complex reaching magnitudes up to 3x106 V m^-1. These fields possibly influence the capture of charged wind-dispersed pollen grains. In this article, we model the electric fields around grounded conductive spherical "plants" and then estimate the forces and resulting trajectories of charged pollen grains approaching the plants. Pollen grain capture depends on many factors: the size, density, and charge of the pollen; the size and location of the plant reproductive structures; as well as wind speed, ambient electric field magnitude, and air viscosity. Electrostatic forces become increasingly important as pollen grain charge increases and pollen grain size (mass) decreases. A positively charged pollen grain is attracted to plants, while a negatively charged pollen grain is repelled. The model suggests that a pollen grain (10 μm radius, carrying a positive charge of 1 fC) is captured if passing within 2 mm of the plant. A similar negatively charged pollen grain is repelled and frequently uncapturable. The importance of electrostatic forces in pollen capture is limited by wind, becoming virtually irrelevant at high wind speeds (e.g. 10 m s^-1). However, during light wind conditions (e.g. 1 m s^-1), atmospheric electricity may be a significant factor in the capture of wind-dispersed pollen.

JOURNAL	Electrostatic Forces in Wind-Pollination: Part 1: Measurement of the Electrostatic Charge on Pollen	03/01/2007

BOWKER, G. E. AND H. C. CRENSHAW. Electrostatic Forces in Wind-Pollination: Part 1: Measurement of the Electrostatic Charge on Pollen. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(8):1587-1595, (2007).
Abstract:	Under fair weather conditions, a weak electric field exists between negative charge induced on the surface of plants and positive charge in the air. This field is magnified around points (e.g. stigmas) and can reach values up to 3x10⁶ V m^-1. If wind-dispersed pollen grains are electrically charged, the electrostatic force (which is the product of the pollen's charge and the electric field at the pollen's location) could influence pollen capture. In this article, we report measurements of the electrostatic charge carried by wind-dispersed pollen grains. Pollen charge was measured using an adaptation of the Millikan oil-drop experiment for seven anemophilous plants: Acer rubrum, Cedrus atlantica, Cedrus deodara, Juniperus virginiana, Pinus taeda, Plantago lanceolata and Ulmus alata. All species had charged pollen, some were positive others negative. The distributions (number of pollen grains as a function of charge) were bipolar and roughly centered about zero although some distributions were skewed towards positive charges. Most pollen carried small amounts of charge, 0.8 fC in magnitude, on average. A few carried charges up to 40 fC. For Juniperus, pollen charges were also measured in nature and these results concurred with those found in the laboratory. For nearly all charged pollen grains, the likelihood that electrostatics influence pollen capture is evident.

JOURNAL	Modeling the Effect of Chlorine Emissions on Ozone Levels Over the Eastern United States	07/01/2007

SARWAR, G. AND P. BHAVE. Modeling the Effect of Chlorine Emissions on Ozone Levels Over the Eastern United States. JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY. American Meteorological Society, Boston, MA, 46(7):1009-1019, (2007).
Abstract:	This paper presents model estimates of the effect of chlorine emissions on atmospheric ozone concentrations in the eastern United States.

JOURNAL	Correcting Photolysis Rates on the Basis of Satellite Observed Clouds	05/17/2007

POUR-BIAZAR, A., R. T. MCNIDER, S. J. ROSELLE, R. SUGGS, G. JEDLOVEC, S. KIM, C. J. LIN, T. C. HO, S. HAINES, B. DORNBLASER, AND R. CAMERON. Correcting Photolysis Rates on the Basis of Satellite Observed Clouds. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES. American Geophysical Union, Washington, DC, 112(D10302):1-17, (2007).
Abstract:	Clouds can significantly affect photochemical activities in the boundary layer by altering radiation intensity, and therefore their correct specification in the air quality models is of outmost importance. In this study we introduce a technique for using the satellite observed clouds to correct photolysis rates in photochemical models. This technique was implemented in EPA's Community Multiscale Air Quality modeling system (CMAQ) and was tested over a ten day period in August 2000 that coincided with the Texas Air Quality Study (TexAQS). The simulations were performed at 4 and 12 km grid size domains over Texas, extending east to Mississippi, for the period of August 24 to August 31, 2000. The results clearly indicate that inaccurate cloud prediction in the model can significantly alter the predicted atmospheric chemical composition within the boundary layer and exaggerate or under-predict ozone concentration. Cloud impact is acute and more pronounced over the emission source regions and can lead to large errors in the model predictions of ozone and its by-products. At some locations the errors in ozone concentration reached as high as 60 ppb which was mostly corrected by the use of our technique. Clouds also increased the lifetime of ozone precursors leading to their transport out of the source regions and causing further ozone production down-wind. Longer lifetime for nitrogen oxides (NO_x=NO+NO₂) and its transport over regions high in biogenic hydrocarbon emissions (in the eastern part of the domain) led to increased ozone production that was missing in the control simulation. Over Houston-Galveston Bay area, the presence of clouds altered the chemical composition of the atmosphere and reduced the net surface removal of reactive nitrogen compounds. Use of satellite observed clouds significantly improved model predictions in areas impacted by clouds. Errors arising from an inconsistency in the cloud fields can impact the performance of photochemical models used for case studies as well as for air quality forecasting. Air quality forecast models often use the model results from the previous forecast (or some adjusted form of it) for the initialization of the new forecast. Therefore, such errors can propagate into the future forecasts and the use of observed clouds in the preparation of initial concentrations for air quality forecasting could be beneficial.

JOURNAL	Sensitivity Analysis and Evaluation of Microfacpm: A Microscale Motor Vehicle Emission Factor Model for Particulate Matter Emissions	04/01/2007

SINGH, R. B., A. H. HUBER, AND J. N. BRADDOCK. Sensitivity Analysis and Evaluation of Microfacpm: A Microscale Motor Vehicle Emission Factor Model for Particulate Matter Emissions. JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION. Air & Waste Management Association, Pittsburgh, PA, 57(4):420-433, (2007).
Abstract:	A microscale emission factor model (MicroFacPM) for predicting real-time site-specific motor vehicle particulate matter emissions was presented in the companion paper entitled "Development of a Microscale Emission Factor Model for Particulate Matter (MicroFacPM) for Predicting Real-Time Motor Vehicle Emissions". The emission rates discussed are in mass per unit distance with the model providing estimates of PM^2.5 and PM¹⁰. This paper complements the companion paper by presenting a sensitivity analysis of the model to input variables, and evaluation model outputs using data from limited field studies. The sensitivity analysis has shown that MicroFacPM emission estimates are very sensitive to vehicle fleet composition, speed, and the percentage of high-emitting vehicles. The vehicle fleet composition can affect fleet emission rates from 8 mg/mi to 1,215 mg/mi; an increase of 5 percent in the smoking (high-emitting) current average US light-duty vehicle fleet (compared to 0%) increased PM2.5 emission rates by approximately 272 percent for 2000; and for the current United States fleet, PM^2.5 emission rates are reduced by a factor of about 0.64 for speeds greater than 50 miles per hour (mi/h) relative to a speed of 10 mi/h. MicroFacPM can also be applied to examine the contribution of emission rates per vehicle class, model year and sources of PM. The model evaluation is presented for the Tuscarora Mountain Tunnel, Pennsylvania Turnpike, PA; and some limited evaluations at two locations - Sepulveda Tunnel, Los Angeles, CA and Van Nuys Tunnel, Van Nuys, CA. In general, the performance of MicroFacPM has shown very encouraging results.

JOURNAL	Observation-Based Assessment of the Impact of Nitrogen Oxides Emissions Reductions on Ozone Air Quality Over the Eastern United States	07/01/2007

GEGO, E., P. PORTER, A. GILLILAND, AND S. RAO. Observation-Based Assessment of the Impact of Nitrogen Oxides Emissions Reductions on Ozone Air Quality Over the Eastern United States. JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY. American Meteorological Society, Boston, MA, 46(7):994-1008, (2007).
Abstract:	Ozone is produced by chemical interactions involving nitrogen oxides (NO_x) and Volatile Organic Compounds (VOCs) in the presence of sunlight. At high concentrations, ground-level ozone has been shown to be harmful to human health and the environment. It has been recognized that ozone is a regional-scale problem and region-wide control strategies would be needed to improve ozone air quality in the eastern United States. To mitigate inter-state transport of ozone and its precursors, the U.S. Environmental Protection Agency issued a regional rule in 1998 known as the 'NO_x SIP Call', requiring 21 states in the eastern United States to reduce their summertime NO_x emissions by May 30, 2004. In this paper, we assess the effectiveness of the new emission control measures mandated by the NO_x SIP call by quantifying the changes that occurred in the daily maximum 8-hr ozone concentrations measured at nearly fifty locations, mostly rural (33 sites of the Clean Air Status and Trend Network and 16 sites of the Air Quality System), over the eastern United States. Given the strong dependence of ozone formation and accumulation on meteorological conditions, we first mitigate the incidence of the latter and extract meteorologically-adjusted ozone concentrations using a multiple regression technique. By examining the differences between the cumulative distribution functions of the meteorologically-adjusted ozone concentrations, we show that ozone concentrations in the eastern U.S. are now on average 13% less than prior to the NO_x SIP call. Using back-trajectory analyses, we also show that emission controls on the electric generating units located in the Ohio River Valley have contributed toward the improvement of ozone air quality in downwind regions, especially east and northeast of the Ohio River Valley.

JOURNAL	A Comparison of Cmaq-Based Aerosol Properties With Improve, Modis, and Aeronet Data	07/19/2007

ROY, B., R. MATHUR, A. GILLILAND, AND S. HOWARD. A Comparison of Cmaq-Based Aerosol Properties With Improve, Modis, and Aeronet Data. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES. American Geophysical Union, Washington, DC, 112(D14 ):1-17, (2007).
Abstract:	We compare select aerosol Properties derived from the Community Multiscale Air Quality (CMAQ) model-simulated aerosol mass concentrations with routine data from the National Aeronautics and Space Administration (NASA) satellite-borne Moderate Resolution Imaging Spectro-radiometer (MODIS) sensor aboard the sun-synchronous Terra Satellite, the NASA's ground-based AErosol RObotic NETwork (AERONET), and the ground-based Interagency Monitoring of PROtected Visual Environment (IMPROVE) Network. The motivation for this analysis is to determine how best to use these parameters in evaluating model predicted PM_2.5 concentrations. CMAQ surface extinction estimates due to scattering at 550 nm wavelength are compared with the IMPROVE nephelometer data obtained from 28 sites within the United States (US). Sulfate fractional Aerosol Optical Depth (AOD) is found to dominate in the northeastern (NE) part of the US; hence, ground-based measurement of sulfate concentrations have been compared with time-series of columnar AOD as observed by the MODIS instrument and also with the CMAQ-predicted tropospheric column values obtained during the June-July-August (JJA) period of 2001. CMAQ surface extinctions are found to be relatively higher than the IMPROVE nephelometer observations; however, there is a good agreement between CMAQ AOD trends and AEROMET and MODIS data, obtained at the seven AERONET sites located in the Eastern U.S. CMAQ is also found to capture the day-to-day variability in the spatial AOD patterns. Monthly average satellite AOD estimates are found to be higher than the AOD data obtained using the CMAQ-predicted aerosol concentrations. Seasonal variation of the satellite-measured aerosol intensive property 'Angstrom exponent' (a gross indicator of the aerosol size distribution) is presented for four selected sites; one each in the Eastern and Central parts and two in the Western part of Continental United States (CONUS). Variability of Angstrom exponent at these four selected sites are analyzed in conjunction with the variation of summer-time AOD (observed and modeled), mass concentrations (observed and modeled) and modeled SO₄ average concentrations during the summer (JJA) period of the year 2001. Annual time series of Angstrom exponent data at the 4 selected sites show a large east-west variation.

JOURNAL	Evaluation of Several PM _2.5 Forecast Models Using Data Collected During the Icartt/Neaqs 2004 Field Study	03/21/2007

MCKEEN, S., S. H. CHUNG, J. WILCZAK, G. A. GRELL, I. DJALALOVA, S. PECKHAM, W. GONG, V. BOUCHET, R. MOFFET, Y. TANG, G. R. CARMICHAEL, R. MATHUR, AND S. YU. Evaluation of Several PM _2.5 Forecast Models Using Data Collected During the Icartt/Neaqs 2004 Field Study. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES. American Geophysical Union, Washington, DC, 112(D10S20):1-20, (2007).
Abstract:	Real-time forecasts of PM_2.5 aerosol mass from seven air-quality forecast models (AQFMs) are statistically evaluated against observations collected in the northeastern U.S. and southeastern Canada from two surface networks and aircraft data during the summer of 2004 ICARTT/NEAQS field campaign. The AIRNOW surface network is used to evaluate PM_2.5 aerosol mass, the U.S. EPA STN network is used for PM_2.5 aerosol composition comparisons, and aerosol size distribution and composition measured from the NOAA P-3 aircraft are also compared. Statistics based on mid-day eight hour averages, as well as twenty four hour averages are evaluated against the AIRNOW surface network. When the eight-hour average PM_2.5 statistics are compared against equivalent ozone statistics for each model, the analysis shows that PM_2.5 forecasts possess nearly equivalent correlation, less bias, and better skill relative to the corresponding ozone forecasts. An analysis of the diurnal variability shows that most models do not reproduce the observed diurnal cycle at urban and suburban monitor locations, particularly during the nighttime to early morning transition. While observations show median rural PM_2.5 levels similar to urban and suburban values, the models display noticeably smaller rural/urban PM_2.5 ratios. The ensemble PM_2.5 forecast, created by combining six separate forecasts with equal weighting, is also evaluated and shown to yield the best possible forecast in terms of the statistical measures considered. The comparisons of PM_2.5 composition with NOAA P-3 aircraft data reveals two important features: 1) the organic component of PM_2.5 is significantly under-predicted by all the AQFMs, and 2) those models that include aqueous phase oxidation of SO₂ to sulfate in clouds over-predict sulfate levels while those AQFMs that do not include this transformation mechanism under-predict sulfate. Errors in PM_2.5 ammonium levels tend to correlate directly with errors in sulfate. Comparisons of PM_2.5 composition with the U.S. EPA STN network for three of the AQFMs show that sulfate biases are consistently lower at the surface than aloft. Recommendations for further research and analysis to help improve PM_2.5 forecasts are also provided.

JOURNAL	Intercomparison Study of Atmospheric Mercury Models: 1. Comparison of Models With Short-Term Measurements	04/15/2007

RYABOSHAPKO, A., R. BULLOCK, J. CHRISTENSEN, M. COHEN, A. DASTOOR, I. ILYIN, G. PETERSEN, D. SYRAKOV, R. S. ARTZ, D. DAVIGNON, R. R. DRAXLER, AND J. MUNTHE. Intercomparison Study of Atmospheric Mercury Models: 1. Comparison of Models With Short-Term Measurements. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier Science Ltd, New York, NY, 376(1-3):228-240, (2007).
Abstract:	Five regional scale models with a horizontal domain covering the European continent and its surrounding seas, one hemispheric and one global scale model participated in an atmospheric mercury modelling intercomparison study. Model-predicted concentrations in ambient air were compared against mercury species observed at four monitoring stations in Central and Northern Europe and a station on the Irish west coast. The modelled concentrations of total particulate mercury (TPM) were generally consistent with the measurements at all sites. The models exhibited significant ability to simulate concentrations of gaseous elemental mercury (GEM), but some of the short-duration peaks at the Central European stations could not be consistently reproduced. Possible reasons for these discrepancies include (1) errors in the anthropogenic emissions inventory utilised; (2) coarse spatial resolution of the models; and (3) uncertainty of natural and re-emitted mercury sources. The largest discrepancies between measurements and modelled concentrations were found for reactive gaseous mercury (RGM). For these models, the uncertainty in predicting short-term (two-week episode) variations of mercury species in air can be characterized by the following overall statistics: 90% of the results for TGM are within a factor of 1.35 of the measurements; for TPM, 90% are within a factor of 2.5; and for RGM, 90% are within a factor of 10.

JOURNAL	Intercomparison Study of Atmospheric Mercury Models: 2. Modeling Results Vs. Long-Term Observations and Comparison of Country Atmospheric Balances	05/15/2007

RYABOSHAPKO, A., R. BULLOCK, J. CHRISTENSEN, M. COHEN, A. DASTOOR, I. ILYIN, G. PETERSEN, D. SYRAKOV, R. S. ARTZ, D. DAVIGNON, R. R. DRAXLER, AND J. MUNTHE. Intercomparison Study of Atmospheric Mercury Models: 2. Modeling Results Vs. Long-Term Observations and Comparison of Country Atmospheric Balances. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier Science Ltd, New York, NY, 377(2-3):319-333, (2007).
Abstract:	Five regional scale models with a horizontal domain covering the European continent and its surrounding seas, two hemispheric and one global scale model participated in the atmospheric Hg modelling intercomparison study. The models were compared between each other and with available measurements from 11 monitoring stations of the EMEP measurement network. Because of very limited number of long-term measurements of Hg available more attention was paid to intercomparison of modelling results. Monthly and annually averaged values of Hg concentrations and depositions as well as items of the Hg atmospheric balances for individual European countries were compared. The models demonstrated good agreement (within ±20%) between annual modelled and observed values of gaseous elemental Hg. Modelled values of Hg wet deposition in Western and Central Europe agreed with the observations within ±45%. Probability to predict wet depositions within a factor of 2 with regard to measurements was 50-70% for all the models. The scattering of modelling results for dry depositions of Hg was more significant (up to ±50% at the annual scale and even higher for monthly data). Contribution of dry deposition to the total Hg deposition was estimated at 30% or higher with elevated dry deposition fluxes during summer time. The participating models agree predicting transboundary pollution for individual countries within ±60% at the monthly scale and within ±30% at the annual scale. All the models predict that the major part of national anthropogenic emissions of Hg is transported outside the country territory.

JOURNAL	Implementing Accountability Within a Multi-Pollutant Air Quality Management Framework	05/01/2007

PENNELL, W., R. SCHEFFE, J. R. BROOK, K. L. DEMERJIAN, G. HIDY, J. VICKERY, AND J. L. WEST. Implementing Accountability Within a Multi-Pollutant Air Quality Management Framework. EM: AIR AND WASTE MANAGEMENT ASSOCIATIONS MAGAZINE FOR ENVIRONMENTAL MANAGERS. Air & Waste Management Association, Pittsburgh, PA, 21-24, (2007).
Abstract:	In 2004, the National Research Council (NRC) published a major assessment of air quality management practices: Air Quality Management in the United States. The assessment resulted from a Congressional directive that the U.S. Environmental Protection Agency commission the National Academy of Sciences to evaluate the effectiveness of the Clean Air Act (CAA) from a scientific and technical perspective and to provide recommendations for strengthening the nation's air quality management system. In the report, the NRC recommends that the United States transition from a pollutant-by-pollutant approach to air quality management to a multi-pollutant, risk-based approach that emphasizes results over process, takes an airshed approach to controlling emissions, creates accountability for these results, and modifies air quality management actions as data on the effectiveness of these actions are obtained.

JOURNAL	A Functional Group Characterization of Organic PM _2.5 Exposure: Results from the Riopa Study	07/01/2007

REFF, A. H., B. TURPIN, J. H. OFFENBERG, C. P. WEISEL, J. ZHANG, M. T. MORANDI, T. STOCK, S. COLOME, AND A. M. WINER. A Functional Group Characterization of Organic PM _2.5 Exposure: Results from the Riopa Study. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(22):4585-4598, (2007).
Abstract:	The functional group (FG) composition of urban residential outdoor, indoor, and personal fine particle (PM_2.5) samples is presented and used to provide insights relevant to organic PM_2.5 exposure. PM_2.5 samples (48 h) were collected during the Relationship of Indoor, Outdoor, and Personal Air (RIOPA) study at 219 non-smoking homes (once or twice) in Los Angeles County, CA, Elizabeth, NJ, and Houston, TX. Fourier transform infrared (FTIR) spectra of PM_2.5 samples were collected, and FG absorbances were quantified by partial least squares (PLS) regression, a multivariate calibration method. There is growing evidence in the literature that a large majority of indoor-generated PM_2.5 is organic. The current research suggests that indoor-generated PM_2.5 is enriched in aliphatic carbon-hydrogen (CH) FGs relative to ambient outdoor PM_2.5. Indoor-generated CH exceeded outdoor-generated CH in 144 of the 167 homes for which indoor or outdoor CH was measurable; estimated indoor emission rates are provided. The strong presence of aliphatic CH FGs in indoor PM_2.5makes particulate organic matter substantially less polar indoors and in personal exposures than outdoors. This is a substantial new finding. Based on the quantified functional groups, the average organic molecular weight (OM) per carbon weight (OC), a measure of the degree of oxygenation of organic PM, is in the range of 1.7-2.6 for outdoor samples and 1.3-1.7 for indoor and personal samples. Polarity or degree of oxygenation effects particle deposition in exposure environments and in the respiratory system.

JOURNAL	Surface and Lightning Sources of Nitrogen Oxides Over the United States: Magnitudes, Chemical Evolution, and Outflow	04/18/2007

HUDMAN, R. C., D. J. JACOB, S. TURQUETY, E. M. LEIBENSPERGER, L. T. MURRAY, S. WU, A. GILLILAND, M. AVERY, T. H. BERTRAM, W. BRUNE, R. C. COHEN, J. E. DIBB, F. M. FLOCKE, A. FRIED, J. HOLLOWAY, J. A. NEUMAN, R. ORVILLE, A. PERRING, X. REN, G. W. SACHSE, H. B. SINGH, A. SWANSON, AND P. J. WOOLDRIDGE. Surface and Lightning Sources of Nitrogen Oxides Over the United States: Magnitudes, Chemical Evolution, and Outflow. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES. American Geophysical Union, Washington, DC, 112(D12S05):1-14, (2007).
Abstract:	We use observations from two aircraft during the ICARTT campaign over the eastern United States and North Atlantic during summer 2004, interpreted with a global 3-D model of tropospheric chemistry (GEOS-Chem) to test current understanding of regional sources, chemical evolution, and export of NO_x. The boundary layer NO_x data provide top-down verification of a 50% decrease in power plant and industry NO_x emissions over the eastern United States between 1999 and 2004. Observed NO_x concentrations at 8-12 km altitude were 0.55 ± 0.36 ppbv, much larger than in previous U.S. aircraft campaigns (ELCHEM, SUCCESS, SONEX) though consistent with data from the NOXAR program aboard commercial aircraft. We show that regional lightning is the dominant source of this upper tropospheric NO_x and increases upper tropospheric ozone by 10 ppbv. Simulating ICARTT upper tropospheric NO_x observations with GEOS-Chem requires a factor of 4 increase in modeled NO_x yield per flash (to 500 mol/flash). Observed OH concentrations were a factor of 2 lower than can be explained from current photochemical models, for reasons that are unclear. A NO_y-CO correlation analysis of the fraction f of North American NO_x emissions vented to the free troposphere as NO_y (sum of NO_x and its oxidation products) shows observed f = 16 ± 10% and modeled f = 14 ± 9%, consistent with previous studies. Export to the lower free troposphere is mostly HNO₃ but at higher altitudes is mostly PAN. The model successfully simulates NO_y export efficiency and speciation, supporting previous model estimates of a large U.S. anthropogenic contribution to global tropospheric ozone through PAN export.

JOURNAL	Probabilistic Characterization of Atmospheric Transport and Diffusion	07/01/2007

IRWIN, J. S., W. B. PETERSEN, AND S. C. HOWARD. Probabilistic Characterization of Atmospheric Transport and Diffusion. JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY. American Meteorological Society, Boston, MA, 46(7):980-993, (2007).
Abstract:	The observed scatter of observations about air quality model predictions stems from a combination of naturally occurring stochastic variations that are impossible for any model to explicitly simulate and variations arising from limitations in our knowledge and from imperfect input data. In this paper, historical tracer experiments of atmospheric dispersion were analyzed to develop algorithms to characterize the observed stochastic variability in the ground-level crosswind concentration profile. The algorithms were incorporated into a Lagrangian puff model, INPUFF, so that the consequences of variability in the dispersion could be simulated using Monte-Carlo methods. The variability in the plume trajectory was investigated in a preliminary sense by tracking the divergence in trajectories from releases adjacent to the actual release location. The variability in the near-centerline concentration values not described by the Gaussian crosswind profile was determined to be on the order of a factor of 2. The variability in the trajectory was determined to likely be larger than the plume width, even with local wind observations for use in characterizing the transport. Two examples are provided to illustrate how estimates of variability 1) can provide useful information to inform decisions for emergency response and 2) can provide a basis for sound statistical designs for model performance assessments.

JOURNAL	Seasonal and Regional Variations of Primary and Secondary Organic Aerosols Over the Continental United States: Semi-Empirical Estimates and Model Evaluation	07/01/2007

YU, S., P. BHAVE, R. L. DENNIS, AND R. MATHUR. Seasonal and Regional Variations of Primary and Secondary Organic Aerosols Over the Continental United States: Semi-Empirical Estimates and Model Evaluation. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 41(13):4690-4697, (2007).
Abstract:	Seasonal and regional variations of primary (OC_pri) and secondary (OC_sec) organic carbon aerosols across the continental U.S. for the year 2001 were examined by a semi-empirical technique using observed OC and elemental carbon (EC) data from 142 routine monitoring sites in mostly rural locations across the U.S, coupled with the primary OC/EC ratios, (OC/EC)_pri,obtained from a chemical transport model (i.e., Community Multiscale Air Quality (CMAQ)model). This application yields the first non-mechanistic estimates of the spatial and temporal variations in OC_pri and OC_sec over an entire year on a continental scale. There is significant seasonal and regional variability in the relative contributions of C_pri and OC_sec to OC. Over the continental U.S., the median OC_sec concentrations are 0.13, 0.36, 0.63, 0.44 and 0.42 µg C m^-3 in winter (DJF), spring (MAM), summer (JJA), fall (SON) and annual, respectively, making 21, 44,51, 42 and 43% contributions to OC respectively. OC_pri exceeds OC_sec in all seasons except summer. Regional analysis shows that the southeastern region has the highest concentration of OC_pri (annual median = 1.35 µg C m^-3), whereas the central region has the highest concentration of OC_sec (annual median = 0.76 µg C m^-3). The mechanistic OC_sec estimates from the CMAQ model were compared against the independently-derived semi-empirical OC_sec estimates. The results indicate that the mechanistic model reproduced the monthly medians of the semiempirical OC_sec estimates well over the northeast, southeast, midwest, and central regions in all months except the summer months (June, July and August), during which the modeled regional monthly medians were consistently lower than the semi-empirical estimates. This indicates that the CMAQ model is missing OC_sec formation pathways that are important in the summer.

JOURNAL	Atmospheric Oxalic Acid and Soa Production from Glyoxal: Results of Aqueous Photooxidation Experiments	11/01/2007

CARLTON, A. M., B. TURPIN, K. E. ALTIERI, S. SEITZINGER, A. H. REFF, H. LIM, AND B. ERVENS. Atmospheric Oxalic Acid and Soa Production from Glyoxal: Results of Aqueous Photooxidation Experiments. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(35):7588-7602, (2007).
Abstract:	Aqueous-phase photooxidation of glyoxal, a ubiquitous water-soluble gas-phase oxidation product of many compounds, is a potentially important global and regional source of oxalic acid and secondary organic aerosol (SOA). Reaction kinetics and product analysis are needed to validate and refine current aqueous-phase mechanisms to facilitate prediction of in-cloud oxalic acid and SOA formation from glyoxal. In this work, aqueous-phase photochemical reactions of glyoxal and hydrogen peroxide were conducted at pH values typical of clouds and fogs (i.e., pH = 4–5). Experimental time series concentrations were compared to values obtained using a published kinetic model and reaction rate constants from the literature. Experimental results demonstrate the formation of oxalic acid, as predicted by the published aqueous phase mechanism. However, the published mechanism did not reproduce the glyoxylic and oxalic acid concentration dynamics. Formic acid and larger multifunctional compounds, which were not previously predicted, were also formed. An expanded aqueous-phase oxidation mechanism for glyoxal is proposed that reasonably explains the concentration dynamics of formic and oxalic acids and includes larger multifunctional compounds. The coefficient of determination for oxalic acid prediction was improved from 0.001 to > 0.8 using the expanded mechanism. The model predicts that less than 1% of oxalic acid is formed through the glyoxylic acid pathway. This work supports the hypothesis that SOA forms through cloud processing of glyoxal and other water-soluble products of alkenes and aromatics of anthropogenic, biogenic and marine origin and provides reaction kinetics needed for oxalic acid prediction.

JOURNAL	A Synthesis of Progress and Uncertainties in Attributing the Sources of Mercury in Deposition	02/01/2007

LINDBERG, S., R. BULLOCK, R. EBINGHAUS, D. ENGSTROM, X. FENG, W. F. FITZGERALD, N. PIRONNE, E. PRESTBO, AND C. SEIGNEUR. A Synthesis of Progress and Uncertainties in Attributing the Sources of Mercury in Deposition. AMBIO. Royal Swedish Academy of Sciences, Stockholm, Sweden, 36(1):19-32, (2007).
Abstract:	A panel of international experts was convened in Madison, Wisconsin, in 2005 as part of the 8th International Conference on Mercury as a Global Pollutant. Our charge was to address the state of science pertinent to source attribution; specifically our key question was "For a given location, can we ascertain with confidence the relative contributions of local, regional and global sources, and of natural versus anthropogenic emissions, to mercury deposition?" The panel synthesized new research pertinent to this question published over the past decade, with emphasis on four major research topics: Long-term Anthropogenic Change, Current Emission and Deposition Trends, Chemical Transformations and Cycling, and Modeling and Uncertainty. The panel drew a series of conclusions within each topic which are presented in this paper. These conclusions led us to concur that the answer to our question is a "qualified yes," with the qualification being dependent upon the level of uncertainty one is willing to accept. We agreed that the uncertainty is strongly dependent upon scale and that our question as stated is answerable with greater confidence both very near and very far from major point sources, assuming that the "global pool" is a recognizable "source". Many regions of interest from an ecosystem-exposure standpoint lie in between, where source attribution carries the greatest degree of uncertainty.

JOURNAL	A Method of Assessing Air Toxics Concentrations in Urban Areas Using Mobile Platform Measurements	11/01/2007

ISAKOV, V., J. TOUMA, AND A. KHLYSTOV. A Method of Assessing Air Toxics Concentrations in Urban Areas Using Mobile Platform Measurements. JOURNAL OF AIR AND WASTE MANAGEMENT. Air & Waste Management Association, Pittsburgh, PA, 57(11):1287-1295, (2007).
Abstract:	The objective of this paper is to demonstrate an approach to characterize the spatial variability in ambient air concentrations using mobile platform measurements. This approach may be useful for air toxic assessments in Environmental Justice applications, epidemiological studies, and environmental health risk assessments. In this study, we developed and applied a method to characterize air toxics concentrations in urban areas using results of the recently conducted field study in Wilmington, Delaware. Mobile measurements were collected over a 4 km by 4 km area of downtown Wilmington for three components: formaldehyde (representative of volatile organic compounds and also photochemically reactive pollutants), aerosol size distribution (representing fine particulate matter), and water-soluble hexavalent chromium (representative of toxic metals). These measurements were used to construct spatial and temporal distributions of air toxics in the area that show a very strong temporal variability, both diurnally and seasonally. An analysis of spatial variability indicates that all pollutants varied significantly by location, which suggests potential impact of local sources. From the comparison with measurements at the central monitoring site, we conclude that formaldehyde and fine particulates show a positive correlation with temperature, which could also be the reason that photochemically-generated formaldehyde and fine particulates over the study area correlate well with the PM2.5 measured at the central site.

JOURNAL	A Hybrid Modeling Approach to Resolve Pollutant Concentrations in An Urban Area	12/01/2007

STEIN, A. F., V. ISAKOV, J. M. GODOWITCH, AND R. R. DRAXLER. A Hybrid Modeling Approach to Resolve Pollutant Concentrations in An Urban Area. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(40):9410-9426, (2007).
Abstract:	A modeling tool that can resolve contributions from individual sources to the urban environment is critical for air-toxics exposure assessments. Air toxics are often chemically reactive and may have background concentrations originated from distant sources. Grid models are the best suited tool to handle the regional features of these chemicals. However, this kind of models can not resolve pollutant concentrations on local scales due to technical and computing time limitations. Moreover, for many species of interest, having reaction time scales that are longer than the travel time across an urban area, chemical reactions can be ignored in describing local dispersion from strong individual sources making lagrangian and plume-dispersion models practical. In this study, we test the feasibility of developing an urban hybrid simulation system. In this combination, the Community Multi-scale Air Quality model (CMAQ) provides the regional background concentrations and urban-scale photochemistry, and local models such as Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT) and AMS/EPA Regulatory Model (AERMOD) provide the more spatially resolved concentrations due to local emission sources. In the initial application, the HYSPLIT, AERMOD, and CMAQ models are used in combination to calculate high resolution benzene concentrations in the Houston area. The study period is from August 18th to September 4th of 2000. The Mesoscale Model 5 (MM5) is used to create meteorological fields with a horizontal resolution of 1x1 km². In another variation to this approach, multiple HYSPLIT simulations with different model inputs and physical parameters are used to create a concentration ensemble to estimate the contribution to the concentration variability from point sources. HYSPLIT simulations are used to model two sources of concentration variability; one due to variability created by different particle trajectory pathways in the turbulent atmosphere and the other due to different flow regimes that might be introduced when using gridded data to represent meteorological data fields. The ensemble mean concentrations determined by HYSPLIT plus the concentrations estimated by AERMOD are added to the CMAQ calculated background to estimate the total mean benzene concentration. These estimated hourly mean concentrations are also compared with available field measurements.

JOURNAL	New Categorical Metrics for Air Quality Model Evaluation	04/01/2007

KANG, D., R. MATHUR, K. L. SCHERE, S. YU, AND B. K. EDER. New Categorical Metrics for Air Quality Model Evaluation. JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY. American Meteorological Society, Boston, MA, 46(4):549-555, (2007).
Abstract:	Traditional categorical metrics used in model evaluations are "clear-cut" measures in that the model's ability to predict an exceedance is defined by a fixed threshold concentration and the metrics are defined by observation-forecast sets that are paired both in space and time. These metrics are informative but limited in evaluating the performance of air quality forecast (AQF) systems because AQF generally examines exceedances on a regional scale rather than a single monitor. New categorical metrics, Weighted Success Index (WSI), Area Hit (aH), and Area False Alarm Ratio (aFAR) are developed. In the calculation of WSI, credits are given to the observation-forecast pairs within the observed exceedance region (missed forecast) or the forecast exceedance region (false alarm) depending on the distance of the points from the central line (perfect observation-forecast match line - 1:1 line on scatter plot).The aH and aFAR are defined by matching observed and forecast exceedances within an area (i.e., model grid cells) surrounding the observation location. The concept of aH and aFAR resembles the manner in which forecasts are usually issued. In practice, a warning is issued for a region of interest such as a metropolitan area if an exceedance is forecast to occur anywhere within the region. The application of these new categorical metrics which are supplemental to the traditional counterparts (critical success index, hit rate, and false alarm ratio) to the Eta-CMAQ forecast system has demonstrated further insight into evaluating the forecasting capability of the system (for example, the new metrics can provide the information about how the AQF system captures the regional signals).

JOURNAL	Diagnostic Model Evaluation for Carbonaceous PM _2.5 Using Organic Markers Measured in the Southeastern U.S.	03/01/2007

BHAVE, P., G. POULIOT, AND M. ZHENG. Diagnostic Model Evaluation for Carbonaceous PM _2.5 Using Organic Markers Measured in the Southeastern U.S. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 41(5):1577-1583, (2007).
Abstract:	Summertime concentrations of fine particulate carbon in the southeastern United States are consistently underestimated by air quality models. In an effort to understand the cause of this error, the Community Multiscale Air Quality (CMAQ) model is instrumented to track primary organic and elemental carbon contributions from fifteen different source categories. The model results are speciated using published source profiles and compared with ambient measurements of 100 organic markers collected at eight sites in the Southeast during the 1999 summer. Results indicate that modeled contributions from vehicle exhaust and biomass combustion - the two largest sources of carbon in the emission inventory - are unbiased across the region. In Atlanta, good model performance for total carbon (TC) is attributed to compensating errors - overestimation of vehicle emissions with underestimations of other sources. In Birmingham, 35% of the TC underestimation can be explained by 2 deficiencies in primary sources. Cigarette smoke and vegetative detritus are not in the inventory, but contribute less than 3% of the TC at each site. After the model results are adjusted for source-specific errors using the organic-marker measurements, an average of 1.6 µgC m^-3 remain unapportioned. This corresponds to 27-39% of ambient TC concentrations at urban sites and up to 56% at rural sites. The most likely sources of unapportioned carbon are discussed.

JOURNAL	Evaluation of the Community Multiscale Air Quality (Cmaq) Model Version 4.5: Uncertainties and Sensitivities Impacting Model Performance: Part I Ozone	12/01/2007

APPEL, W., A. GILLILAND, G. SARWAR, AND R. C. GILLIAM. Evaluation of the Community Multiscale Air Quality (Cmaq) Model Version 4.5: Uncertainties and Sensitivities Impacting Model Performance: Part I Ozone. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(40):9603-9613, (2007).
Abstract:	This study examines ozone (O₃) predictions from the Community Multiscale Air Quality (CMAQ) model version 4.5 and discusses potential factors influencing the model results. Daily maximum 8-hr average O₃ levels are largely underpredicted when observed O₃ levels are above 85 ppb and overpredicted when they are below 35 ppb. Using a clustering approach, model performance was examined separately for several different synoptic regimes. Under the most common synoptic conditions of a typical summertime Bermuda High setup, the model showed good overall performance for O₃, while associations have been identified here between other, less frequent, synoptic regimes and the O₃overprediction and underprediction biases. A sensitivity test between the CB-IV and CB05 chemical mechanisms showed that predictions of daily maximum 8-hr average O₃ using CB05 were on average 7.3 % higher than those using CB-IV. Boundary condition (BC) sensitivity tests show that the overprediction biases at low O₃ levels are more sensitive to the BC O₃levels near the surface than BC concentrations aloft. These sensitivity tests also show the model performance for O₃ improved when using the global GEOS-CHEM BCs instead of default profiles. Simulations using the newest version of the CMAQ model (v4.6) showed a small improvement in O₃ predictions, particularly when vertical layers were not collapsed. Collectively, the results suggest that key synoptic weather patterns play a leading role in the prediction biases, and more detailed study of these episodes are needed to identify further modeling improvements.

JOURNAL	The Use of Air Quality Forecasts to Assess Impacts of Air Pollution on Crops: Methodology and Case Study	12/01/2007

TONG, D., R. MATHUR, K. L. SCHERE, D. KANG, AND S. YU. The Use of Air Quality Forecasts to Assess Impacts of Air Pollution on Crops: Methodology and Case Study. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(38):8772-8784, (2007).
Abstract:	It has been reported that ambient ozone (O₃), either alone or in concurrence with acid rain precursors, accounts for up to 90% of U.S. crop losses resulting from exposure to all major air pollutants. Crop damage due to O₃ exposure is of particular concern as ambient concentrations remain high in many major food producing regions. Assessing O₃ damage to crops is challenging due to the difficulties in determining the reduction in crop yield that results from exposure to surface O₃, for which monitors are limited and mostly deployed in non-rural areas. This work explores the potential benefits of using operational air quality forecast (AQF) data to estimate rural O₃ exposure. Using the results from the first nationwide air quality forecast as a case study, we demonstrate how the O₃ data provided by AQF can be combined with concurrent crop information to assess O₃ damages to soybeans in the United States. We estimate that exposure to ambient O₃ reduces the US soybean production by 10% in 2005.

JOURNAL	Scientific Uncertainties in Atmospheric Mercury Models II: Sensitivity Analysis in the Conus Domain	10/01/2007

LIN, C., P. PONGPRUEKSA, R. BULLOCK, S. LINDBERG, S. O. PEHKONEN, C. JANG, T. BRAVERMAN, AND T. C. HO. Scientific Uncertainties in Atmospheric Mercury Models II: Sensitivity Analysis in the Conus Domain. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(31):6544-6560, (2007).
Abstract:	In this study, we present the response of model results to different scientific treatments in an effort to quantify the uncertainties caused by the incomplete understanding of mercury science and by model assumptions in atmospheric mercury models. Two sets of sensitivity simulations were performed to assess the uncertainties using modified versions of CMAQ-Hg in a 36-km Continental United States domain. From Set 1 Experiments, it is found that the simulated mercury dry deposition is most sensitive to the Gaseous Elemental Mercury (GEM) oxidation product assignment, and to the implemented dry deposition scheme for GEM and Reactive Gaseous Mercury (RGM). The simulated wet deposition is sensitive to the aqueous Hg(II) sorption scheme, and to the GEM oxidation product assignment. The inclusion of natural mercury emission causes a small increase in GEM concentration but has little impact on deposition. From Set 2 Experiments, it is found that both dry and wet deposition are sensitive to mercury chemistry. Change in model mercury chemistry has a greater impact on simulated wet deposition than on dry deposition. The kinetic uncertainty of GEM oxidation by O₃ and mechanistic uncertainty of Hg(II) reduction by aqueous HO₂ pose the greatest impact. Using the upper-limit kinetics of GEM-O₃ reaction or eliminating aqueous Hg(II)-HO₂ reaction results in unreasonably high deposition and depletion of gaseous mercury in the domain. Removing GEM-OH reaction is not sufficient to balance the excessive mercury removal caused by eliminating the HO₂ mechanism. Field measurements of mercury dry deposition, better quantification of mercury air-surface exchange and further investigation of mercury redox chemistry are needed for reducing model uncertainties and for improving the performance of atmospheric mercury models.

JOURNAL	Building Resolving Large-Eddy Simulation and Comparison With Wind Tunnel Experiments	11/10/2007

SMOLARKIEWICZ, P. K., R. SHARMAN, J. WEIL, S. G. PERRY, D. HEIST, AND G. E. BOWKER. Building Resolving Large-Eddy Simulation and Comparison With Wind Tunnel Experiments. JOURNAL OF COMPUTATIONAL PHYSICS. Elsevier Science Ltd, New York, NY, 227(1):633-653, (2007).
Abstract:	This journal article describes numerical modeling with large-eddy simulations (LES) of flow and turbulence around a complex building structure (the Pentagon building). The LES is compared to wind tunnel simulations for the same model building in a neutral atmospheric boundary layer. The results indicate that the LES approach was able to reproduce the general features of the neutral boundary layer wind tunnel flow and dispersion findings. Additionally, LES simulations of flow over the Pentagon building with a stratified boundary layer suggest significantly effects of atmospheric stability. LES approaches are much more computationally efficient than Computational Fluid Dynamics models that are normally required to simulate the complexities of flow in urban situations.

JOURNAL	(Amd) Analysis of Air Quality Data Near Roadways Using a Dispersion Model	12/01/2007

VENKATRAM, A., V. ISAKOV, E. D. THOMA, AND R. W. BALDAUF. (Amd) Analysis of Air Quality Data Near Roadways Using a Dispersion Model. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 41(40):9481-9497, (2007).
Abstract:	We used a dispersion model to analyze measurements made during a field study conducted by the U.S. EPA in July-August 2006, to estimate the impact of traffic emissions on air quality at distances of tens of meters from an 8 lane highway located in Raleigh, North Carolina. The air quality measurements consisted of long path optical measurements of NO at distances of 7 m and 17 m from the edge of the highway. Sonic anemometers were used to measure wind speed and turbulent velocities at 6 m and 20 m from the highway. Traffic flow rates were monitored using traffic surveillance cameras. The dispersion model (Venkatram, 2004) explained over 60% of the variance of the observed path averaged NO concentrations, and over 90% of the observed concentrations were within a factor of two of the model estimates. Sensitivity tests conducted with the model indicated that the traffic flow rate made the largest contribution to the variance of the observed NO concentrations. The meteorological variable that had the largest impact on the near road NO concentrations was the standard deviation of the vertical velocity fluctuations, w σ . Wind speed had a relatively minor effect on concentrations. Furthermore, as long as the wind direction was within plus or minus 45º from the normal to the road, wind speed had little impact on near road concentrations. The measurements did not allow us to draw conclusions on the impact of traffic induced turbulence on dispersion. The analysis of air quality and meteorological observations resulted in plausible estimates of on-road emission factors for NO. The performance of the dispersion model in explaining NO observations suggests that appropriate air quality measurements coupled with dispersion modeling can be used to estimate on-road emission factors of other species, such as VOCs.

JOURNAL	Linking Air, Land, and Water Pollution for Effective Environmental Management	12/01/2007

RAO, S. Linking Air, Land, and Water Pollution for Effective Environmental Management. EM: AIR AND WASTE MANAGEMENT ASSOCIATIONS MAGAZINE FOR ENVIRONMENTAL MANAGERS. Air & Waste Management Association, Pittsburgh, PA, 5, (2007).
Abstract:	Since the passage of the National Environmental Policy Act in 1970, the U.S. Environmental Protection Agency, other federal agencies, and the states have made substantial progress in improving the Nation’s air and water quality. Traditionally, the air, land, and water pollution control programs are managed rather independently of each other, in part, due to differing funding allocations and separate sets of rules and regulations. Several articles in this EM issue discuss the need for integrated assessments of air, land, and water pollution and the resulting challenges confronting the environmental managers.

JOURNAL	Sulfur and Nitrogen Deposition on Ecosystems in the United States	12/01/2007

DENNIS, R. L., R. HAEUBER, T. Blett, J. Cosby, C. Driscoll, J. Sickles, AND J. M. JOHNSTON. Sulfur and Nitrogen Deposition on Ecosystems in the United States. EM: AIR AND WASTE MANAGEMENT ASSOCIATIONS MAGAZINE FOR ENVIRONMENTAL MANAGERS. Air & Waste Management Association, Pittsburgh, PA, 12-17, (2007).
Abstract:	The ecological impacts of atmospheric sulfur and nitrogen deposition first gained attention in the United States in the early 1970s with reports of "acid rain" falling to earth, causing lakes and streams to become acidic and resulting in conditions that were unsuitable for reproduction and survival of fish in those waters. Many years of research in the U.S., Canada, and Europe have since confirmed the link between acidic deposition and ecosystem health. Today, there is a much greater understanding of the complex interactions between sulfur and nitrogen deposition and the natural environment. The impacts of these pollutants are not limited to “acid rain” alone, but are also related to issues as diverse as elevated ozone concentrations in the lower atmosphere, fish mercury levels, and the trophic status of downstream coastal estuaries.

JOURNAL	Ecological Forecasting: Microbial Contamination and Atmospheric Loadings of Nutrients to Land and Water	12/01/2007

MATHUR, R., W. E. FRICK, G. LEAR, AND R. L. DENNIS. Ecological Forecasting: Microbial Contamination and Atmospheric Loadings of Nutrients to Land and Water. EM: AIR AND WASTE MANAGEMENT ASSOCIATIONS MAGAZINE FOR ENVIRONMENTAL MANAGERS. Air & Waste Management Association, Pittsburgh, PA, 36-40, (2007).
Abstract:	The development of ecological forecasts, namely, methodologies to predict the chemical, biological, and physical changes in terrestrial and aquatic ecosystems is desirable so that effective strategies for reducing the adverse impacts of human activities and extreme natural events can be developed to sustain ecosystem productivity. The temporal and spatial scales of such ecological forecasts would, in turn, depend on the ecosystem and the phenomenon being forecast. Since the development of comprehensive monitoring programs for ecological assessments and forecasting is expensive, scientists and managers would need to increasingly rely on theoretical models for understanding nutrient effects and forecasting trends. Systems that include detailed description of the pathways dictating the transport and fate of nutrients and contaminants from a combined atmosphere-land-water perspective are needed for integrated ecological assessments. Such systems must be able to accurately describe not only the cycling and residence time of the contaminants in the individual media, but also the interactions from an integrated multi-media perspective. Significant efforts have been devoted over the past two decades toward the development of detailed models addressing specific ecological problems. In recent years, several such efforts have been transitioned to provide short-term forecast of air and water quality. Linking the information from these evolving modeling systems could provide building blocks for the next generation integrated ecological forecast models. Additionally, the development of continual archives of the model output from these systems could provide vital long-term database whose analysis in conjunction with available monitored data will help better characterize both the short and long-term response of key ecological variables on spatial scales ranging from local to regional.

PAPER IN NON-EPA PROCEEDINGS	Relationships Between Nitrogen Oxide Emissions from Electrical Generating Units in the U.S. and Meteorology	08/01/2007

PORTER, S., S. RAO, AND E. L. GEGO. Relationships Between Nitrogen Oxide Emissions from Electrical Generating Units in the U.S. and Meteorology. In Proceedings, NATO/CCMS 28th International Technical Meeting, Leipzig, GERMANY, May 15 - 19, 2006. Elsevier Science BV, Amsterdam, Netherlands, 793-794, (2006).
Abstract:	Nitrogen oxide (NO_x) emissions from electrical generating units (EGUs) in the northeast US have declined dramatically during the past few years as a result of a series of air quality rules (RACT rule, Clean Air Act Amendments Title IV, and the NO_x SIP call). Progress in reducing NOx emissions is evident in continuous NO_x measurements collected by EGUs. These measurements are collected hourly from roughly 1,500 EGUs and are archived at EPA's Clean Air Market Division, (USEPA, 2006a). NO_x data collected by EGUs also have value as a source of information important to air quality modeling. Declining NO_x emissions are most evident during the summer ozone season when seasonal controls are in effect, and have occurred despite offsetting increases in heat input (HI), the energy content of fuel used to generate electricity (also archived by EPA's Clean Air Market Division). Weather indirectly affects NO_x emissions (and therefore air quality) by influencing the amount of fuel used for cooling and heating. Here we examine time scales common to both HI and meteorology with the goal of improving the performance of air quality modeling and forecasting.

PAPER IN NON-EPA PROCEEDINGS	Modeling Assessment of the Impact of Nitrogen Oxides Emission Reductions on Ozone Air Quality in the Eastern United States: Offsetting Increases in Energy Use	08/01/2007

PORTER, S., E. GEGO, A. GILLILAND, C. HOGREFE, J. M. GODOWITCH, AND S. RAO. Modeling Assessment of the Impact of Nitrogen Oxides Emission Reductions on Ozone Air Quality in the Eastern United States: Offsetting Increases in Energy Use. In Proceedings, 28th NATO/CCMS International Technical Meeting, Leipzig, GERMANY, May 15 - 19, 2006. Elsevier Science BV, Amsterdam, Netherlands, 177-188, (2007).
Abstract:	The objective of this study is to examine changes in ambient ozone concentrations estimated by a photochemical air quality model in response to the NOx emission reductions imposed on the utility sector. To accomplish this task, CMAQ air quality model simulations were performed with three distinct sets of emission fields. The first two scenarios simulate actual 2002 and 2004 emissions as best inferred from available emission data. These scenarios characterize emissions before and after implementation of the NO_x SIP Call, respectively. The third scenario represents a hypothetical rendering of NO_x emissions in 2002 had there been no emission controls imposed on the utility sector. All components of the no control scenario are identical to those of the 2002 scenario,except the point source emissions that were obtained by multiplying the 2002 heat input(electricity demand) with the emission rates (kg NO_x emitted/mmBTU utilized) in 1997. The modeling results show that the implementation of the NO_x SIP Call led to a decline in the maximum ozone concentrations in most of the eastern US. A decrease ranging from 3% to 5% was widely identifed between the median 8–hr daily maximum concentrations modeled for 2004 and 2002. However, the fourth-highest modeled values decreased by 5 - 8%. Without controls on the utility sector, total emissions in 2002 would have been 40% higher than they actually were in 2002. However, while ozone concentrations would have been higher in most of the domain without the NO_x SIP Call, local areas surrounding major sources would actually have had 8-hr daily maximum concentrations 7% to 8% lower.

PRESENTATION	Speciate EPA's Database of Speciated Emission Profiles	02/22/2007

HOUYOUX, M., D. BECK, AND D. MOBLEY. Speciate EPA's Database of Speciated Emission Profiles. Presented at AWMA Webcast , Research Triangle Park, NC, February 22, 2007.
Abstract:	SPECIATE is the U.S. Environmental Protection Agency's (EPA) repository of total organic compound (TOC) and particulate matter (PM) speciation profiles for emissions from air pollution sources. The data base has recently been updated and an associated report has recently been released. Among the many uses of speciation data, these source profiles are used to: 1) create speciated emissions inventories for regional haze, particulate matter with an aerodynamic diameter less than 2.5 micrometers (PM2.5), and ozone (O3) air quality modeling; 2) estimate hazardous and toxic air pollutant emissions from total PM and TOC primary emissions; 3) provide input to chemical mass balance (CMB) receptor models; and, 4) verify profiles derived from ambient measurements using multivariate receptor models (e.g., factor analysis and positive matrix factorization). To date, the initiative to update SPECIATE has produced: 2,865 PM profiles (1,504 legacy profiles, plus 1,361 new profiles of which 95 are simplified profiles); 1,215 gas profiles, 648 of which are new profiles; a total of 1,902 unique species; composite profiles for 58 (47 PM and 11 VOC) source categories; an updated SCC-to-Profile cross-reference table accounting for over 80% of national VOC and nationwide PM emissions in the draft 2002 National Emissions Inventory (NEI); VOC-to-TOG conversion factors for applicable gas profiles; a protocol for expansion of the database; a mapping of the new VOC compounds into model species categories; and review and prioritization of 49 studies entailing 614 PM and 822 VOC profiles for potential future inclusion in the SPECIATE database. Find out the latest information available on emission profiles during the Air & Waste Management Association's Audio + Web Conference on February 22, 2007 at 2:00 ET when experts discuss the latest update to the SPECIATE data base.

PRESENTATION	Air Quality Over the Eastern United States	02/28/2007

RAO, S. Air Quality Over the Eastern United States. Presented at New York Academy of Sciences Regional and Urban Air Quality, New York, NY, February 28, 2007.
Abstract:	Atmospheric concentrations of ozone and fine particulate matter continue to exceed their standards in many parts of the eastern United States. However, the peak concentration levels and number of ozone exceedances have decreased substantially in recent years due, in part, to the implementation of the NOx SIP Call over the eastern United States by May 2004. Using the ozone observations and air quality models, we illustrate the impact of emission controls on the electric generating units and present research that is underway to better understand the relationships between air quality and human health.

PRESENTATION	Soa from Isoprene Oxidation Products: Model Simulation of Cloud Chemistry	02/25/2007

CARLTON, A. G., S. J. ROSELLE, AND R. MATHUR. Soa from Isoprene Oxidation Products: Model Simulation of Cloud Chemistry. Presented at Gordon Conference for Biogenic Hydrocarbons and the Atmosphere, Ventura, CA, February 25 - March 02, 2007.
Abstract:	Recent laboratory evidence supports the hypothesis that secondary organic aerosol (SOA) is formed in the atmosphere through aqueous-phase reactions in clouds. The results of batch photochemical reactions of glyoxal, methylglyoxal and hydrogen peroxide are presented. These laboratory results were incorporated into a CMAQ and a model simulation of the Eastern U.S. for August 2004, on a 12 km grid was performed. Model results are presented and implications are discussed.

PRESENTATION	Facilitating Advanced Urban Meteorology and Air Quality Modeling Capabilities With High Resolution Urban Database and Access Portal Tools	03/27/2007

CHING, J. K., A. HANNA, F. CHEN, S. BURIAN, AND T. HULTGREN. Facilitating Advanced Urban Meteorology and Air Quality Modeling Capabilities With High Resolution Urban Database and Access Portal Tools. Presented at Proceedings of the Sixth International Urban Air Quality Conference, Limassol, CYPRUS, March 27 - 29, 2007.
Abstract:	Information of urban morphological features at high resolution is needed to properly model and characterize the meteorological and air quality fields in urban areas. We describe a new project called National Urban Database with Access Portal Tool, (NUDAPT) that addresses this need. NUDAPT is designed to produce gridded fields of urban canopy parameterizations to improve urban meteorological simulations given the availability of new high-resolution data of urban buildings and land use. An important core-design feature is the utilization of Portal technology to enable NUDAPT to be a "Community" based system. Sensitivity studies showing air quality simulations driven with outputs from urban meteorology preprocessors using advanced urban descriptions are described.

PRESENTATION	Wind Tunnel Simulations of Pollution from Roadways	08/29/2007

HEIST, D., S. G. PERRY, L. BRIXEY, AND G. E. BOWKER. Wind Tunnel Simulations of Pollution from Roadways. Presented at PHYSMOD 2007, Orleans, FRANCE, August 29 - 31, 2007.
Abstract:	A wind tunnel study has been conducted to examine the influence of roadway configurations and nearby structures on the flow and dispersion of traffic related pollutant concentrations within a few hundred meters of the roadway. The study focused four selected configurations (all with a model six-lane, divided highway at a 1:150 scale). They included flat terrain with no structures, flat terrain with sound barriers and/or vegetation barriers, an elevated highway, and road cuts. Experiments involved smoke visualization and tracer concentration measurements from a uniform line-type source as well as flow characterization.

PRESENTATION	Evaluating and Using Air Quality Models	03/27/2007

RAO, S., A. GILLILAND, K. FOLEY, AND C. HOGREFE. Evaluating and Using Air Quality Models. Presented at International Conference on Urban Air Quality, Limassol, CYPRUS, March 27 - 29, 2007.
Abstract:	Grid-based models are being used to assess the magnitude of the pollution problem and to design emission control strategies to achieve compliance with the relevant air quality standards in the United States.

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