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1999 Progress Report: A Modeling Investigation of NHx Cycling in the Troposphere and Its Impact on Particulate Matter and Acidic Substances Budgets

EPA Grant Number: R826773
Title: A Modeling Investigation of NHx Cycling in the Troposphere and Its Impact on Particulate Matter and Acidic Substances Budgets
Investigators: Mathur, Rohit , Coats, Carlie J. , Houyoux, Marc , McHenry, John , Shankar, Uma
Current Investigators: Mathur, Rohit , Adelman, Zac , Alapaty, Kiran , Houyoux, Marc , Shankar, Uma
Institution: MCNC / North Carolina Supercomputing Center
EPA Project Officer: Shapiro, Paul
Project Period: October 1, 1998 through September 30, 2001 (Extended to March 31, 2003)
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $488,744
RFA: Air Pollution Chemistry and Physics (1998)
Research Category: Engineering and Environmental Chemistry

Description:

Objective:

The fate of nitrogen-containing species in the atmosphere is of considerable interest given their role in the formation of acidic substances, particulate matter, and tropospheric ozone, and potential eutrophication and nutrient loading effects resulting from their deposition. The overall objective of this research is to improve current understanding of the cycling of reduced nitrogen compounds in the atmosphere and to investigate the coupling of such compounds with atmospheric aerosols and other criteria pollutants responsible for the acidifying atmospheric load through the development, enhancement, and continuous evaluation of comprehensive multipollutant regional models.

Progress Summary:

To synthesize the current knowledge of the processes governing the fate of NHx in a consistent modeling framework, and to develop a preliminary assessment of the adequacy of existing NH3 emissions, the Regional Acid Deposition Model (RADM) was enhanced by adding several additional modules to represent the various atmospheric physical and chemical pathways governing the fate of emitted NH3. A module to represent aerosol equilibrium was developed and added to the RADM framework. The module, based on the work of Saxena et al. (1986) and further modifications by Binkowski and Shanker (1995) and Binkowski and Ching (1996), calculates chemical composition of sulfate-nitrate-ammonium-water aerosol based on equilibrium thermodynamics. In addition, modules were developed for advective and turbulent transport and dry deposition of the additional particulate species, and the representation of aqueous chemistry, cloud transport, and scavenging were enhanced to include the contribution of the additional particulate phase species. The resulting version of the model is referred to as the Extended RADM. Regional simulations with the Extended RADM were conducted over the eastern United States for 30 cases. Input emissions for NH3 were derived from the 1985 NAPAP inventory, while those for all other emitted species were based on the EPA 1990 inventory. Chang et al. (1990) note that the NH3 estimates in the 1985 inventory could differ by a factor of from two to perhaps as much as five. To account for this bias, we developed seasonal correction factors for NH3 emission estimates through successive model applications and comparisons with observed data. This simple model inversion method allows for developing a modeling inventory that provides model results that are consistent with observed values for both ambient concentrations and wet deposition amounts, and provides a starting point for exploration of the cycling of reduced nitrogen in the troposphere. The model aggregated seasonal and annual predictions that were compared against observed data from the CASTNet and NADP/NTN networks. These comparisons suggest that the model can reasonably well capture the spatial and seasonal trends in ambient concentrations and wet deposition amounts of various species, as well as the relative gas-aerosol partitioning of both the reduced and oxidized forms of nitrogen.

A limiting feature of the Extended-RADM is the lack of treatment of particulate matter (PM) size distribution. Additionally, the current treatment of cloud processes based on convective clouds results in overprediction of wet deposition amounts during the cold seasons. To address these limitations, we also have initiated simulations with the gas-aerosol version of the Multiscale Air Quality Simulation Platform (MAQSIP) over: (1) the eastern United States (grid resolution of 36 km); and (2) finer scale (12 km) simulations over North Carolina and surrounding states to simulate the impact of the high NH3 emissions in eastern North Carolina. A number of model enhancement activities also were initiated during the reporting period and include: (1) a preliminary investigation of the use of an alternate thermodynamic aerosol equilibrium module (ISORROPIA by Nenes et al., 1998) in MAQSIP to include additional inorganic aerosol components; (2) enhancement of the aerosol-cloud processor; and (3) interfacing the aqueous chemistry calculations with different gas-phase chemical mechanisms.

Efforts also were devoted towards developing current emission inputs for the model. These included enhancing the Sparse Matrix Operator Kernel Emissions (SMOKE) modeling system to facilitate emission inventory processing for additional species including SO2, NH3, PM10, and PM2.5. The NH3 data were derived in two steps. First, they were grown from the 1990 inventory using economic projection factors. Second, they were recomputed in some cases (mainly agricultural activities) using updated emission factors taken from a 1995 study that we had conducted. The SO2 data also were projected from 1990, with the exception of the use of updated 1995 data from electric utilities. The PM data were simply "grown" from 1990, at least for PM due to human activities.

Future Activities:

The emissions inputs will be updated with the recent 1996 NET inventory and the 1996 Continuous Emissions Monitoring (CEM) data for CO, VOC, NOx, and SO2. We also will investigate improvements in spatial allocation of NH3 sources through the use of a data set containing location of individual livestock farms. Methods to introduce seasonal variation in NH3 emissions will be investigated.

The anticipated model enhancement activities include: testing and assessment of alternate aerosol equilibrium modules; interfacing the multiscale cloud-chemistry package with the MAQSIP gas-aerosol model; investigating potential improvements in dry-deposition velocity estimates for NH3; and initiating the development of an inverse modeling methodology.

Model simulations with the updated emissions will be conducted to: (1) study the sensitivity to grid resolution; (2) determine range of influence of reduced and oxidized nitrogen; and (3) study impact of potential reductions in NOx and increases in NH3 emissions on PM composition.

References:

Binkowski FS, Ching JKS. Regional scale distribution of fine particulate mass and visibility from the EPA regional particulate model. In: Proceedings of the Ninth AMS-A&WMA Joint Conference on Applications of Air Pollution Meteorology, Atlanta, GA, January 28–February 2, 1996.

Binkowski FS, Shankar U. The regional particulate matter model 1. Model description and preliminary results. J Geophys Res 1995;100:(26)191-209.

Chang JS, Brost RA, Isaksen ISA, Madronich S, Middleton P, Stockwell WR, Walcek CJ. A three-dimensional eulerian acid deposition model: physical concepts and formulation. J Geophys Res 1987;92:14681-14700.

Chang JS, Binkowski FS, Seaman NL, Byun DW, McHenry JN, Samson PJ, et al. The regional acid deposition model and engineering model, NAPAP SOS/T report 4. In: National Acid Precipitation Assessment Program, Acidic Deposition: State of Science and Technology, Volume I, Washington, DC, 1990.

Nenes A, Plinis C, Pandis S. User’s guide for the “ISORROPIA” thermodynamic equilibrium aerosol model. Division of Marine and Atmospheric Chemistry of the Rosenstiel School of Marine and Atmospheric Science, University of Miami, FL, 1998.

Saxena P, Hudischewskyj AB, Seigneur C, Seinfeld JH. A comparative study of equilibrium approaches to the chemical characterization of secondary aerosols. Atmos Environ 1986;20:1471ff.

Journal Articles:

No journal articles submitted with this report: View all 11 publications for this project

Supplemental Keywords:

air, atmospheric chemistry, chemical transport, regional models, model evaluation. , Air, Scientific Discipline, RFA, Engineering, Chemistry, & Physics, Ecology, Environmental Chemistry, tropospheric ozone, fate and transport, regional scale, sulfur, ambient air, fine particles, ozone, eutrophication, aerosol particles, nitrogen removal, oxides, ambient aerosol particles, troposphere, particulates, PM2.5, particulate matter, air modeling, air pollution models, ambient aerosol, human exposure
Relevant Websites:

http://www.envpro.ncsc.org/
http://www.envpro.ncsc.org/products/maqsip/
http://www.envpro.ncsc.org/products/smoke/SMOKEV1.html#enhance

Progress and Final Reports:
Original Abstract
2000 Progress Report
2001 Progress Report
2002 Progress Report
Final Report

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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