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Analysis of Air Quality Monitoring Results for N-Species
Research Programs
The main goal of this effort is to analyze and interpret environmental (primarily atmospheric) data to document observable changes in environmental stressors that may be associated with emissions reductions required by various legislation (i.e., Clean Air Act Ammendments of 1990 [CAAA], state implementation plans, and Clear Skies Presidential initiative). The main emphasis is on nitrogen-containing species (N-species).
Background
Clean Air Status and Trends Network (CASTNET) monitors air and other environmental quality parameters at rural sites located primarily in the eastern U.S. Monitoring began at 16 sites in 1987, and the network has grown over the years to the current number of approximately 80 sites (50 in the east). Data are collected year round at most sites. The CASTNET database contains information on atmospheric concentration (continuous O3 and seekly SO2, SO4, HNO3, and NH4). There are also continuous meteorological data and hourly estimates of deposition velocity at each monitoring site, and weekly wet deposition is monitored at selected CASTNET sites by the National Acid Deposition Program (NADP). Weekly wet depostion data is available from NADP at sites witin 50km of those CASTNET sites that so not have wet monitors.
NOx Accountability
Several preliminary analyses by NERL, LCB scientists addressed airborned S and N stressor concentrations, spatial distributions, and changes using concentration data collected between 1989 and 1995 at CASTNET sites located inthe eastern United States (U.S.) [re. 1-3]. Early published studies of CASTNET concentration data have shown strong declines of airborne concentrations of both SO2 and sulfates, but little change in N concentrations. These results are generally consistent with emissions changes over the same period, especially the CAAA-mandated Phase I controls on emissions from electric power generation that became effective in January of 1995.
General Research Description
The primary emphasis is to extend earlier analyses using a more comprehensive data set. In performing these analyses, S and N data will be assembled from the CASTNET, NADP, and other pertinent data archives, as available. Data quality issues with the CASTNET data have been recently addressed to ensure compatibility of merged data sets, and several peer-reviewed publications have been completed on this topic [ref. 4-7]. Data will include airborne concentration, deposition velocity, and dry deposition estimates from CASTNET and wet deposition results from both CASTNET and NADP. In the currently proposed effort, emissions, concentration, and deposition data will be examined in an effort to define spatial patterns and temporal behavior. The research will focus on: annual and seasonal distributions and behavior; chemical form and delivery medium; influence of monitoring-site location and meteorology; behavior of deposition; environmentally-unadjusted changes in deposition (as they relate to exposure); and impacts of Phase I of the CAAA. The research will be conducted in phases: analysis of the spatial and seasonal distribution of S and N in the eastern U.S. and smaller subregions; and analysis of regional and site-specific changes in the behavior of atmospheric S and N stressors.
Research Tasks
- Descriptive analyses will be performed. Statistical data summaries and analyses will be performed. These analyses will use data summaries such as annual and seasonal averages of specific pollutant behavior to focus on the regional and seasonal nature of air quality and deposition of S and specifically N in the eastern US. As an example, regional analyses may compare results from a source area (e.g., Ohio Valley) with those downwind (e.g., Northeast), perhaps contrasted against background or montane areas (e.g., Ashland, ME or Cranberry, NC). Likewise, seasonal analyses may contrast summer versus winter results. A prototype analysis has been performed that addressed airborne S and N stressor concentrations for the Northeastern US using the 1989-1995 CASTNET data record [ref. 2]. The current analysis is expected to be similar, but more comprehensive (i.e., covering concentration and deposition for most of the eastern US).
- Results will be interpreted considering the temporal nature of emissions as well as the seasonal influences of atmospheric chemistry and meteorological processes that transform them prior to their deposition. Linkage of changes in emissions and deposition requires an air quality model. CMAQ runs have been performed for the eastern US under identical 1995 summertime (July) meteorology using pre- and post-Phase I emissions. Additional model runs will be analyzed as they become available. These predictions will be used (as available) to aid in the interpretation of summertime monitoring results. The relative contributions of wet and dry processes will be sought. Regional behavior will also be examined to provide insight on the influence of latitude and proximity to sources on the resulting environmental quality. Maps will be created to illustrate and contrast the spatial distribution and behavior of emissions and resulting environmental quality.
- CASTNET has subsumed much of NOAA's dry deposition network and data archive (AIRMoN-Dry). As a result, examination of measurements at the current CASTNET and AIRMoN-Dry sites is needed to document differences and define the adjustments required to have both data sets on the same basis. N-data from other monitoring networks (e.g., IMPROVE) will also be available and will be examined as time and data availability permit.
Much of our effort will focus on preparing N deposition maps for the eastern U.S. and selected regions [ref.8-9]. Both oxidized [ref.10] and reduced forms of N will be addressed to provide estimates of distributions and patterns of N stressors including wet and dry concentrations and deposition flux available for selected geographic areas. It is expected that recent legislation (e.g., Phase II of the CAAA; OTC and Section 126 NOx Budget Trading; and the NOx SIP call) will be becoming apparent in the monitoring data by the 2005 time frame. Results from the current study are expected to provide insight on the baseline environmental conditions prevailing prior to these recent legislative impacts. This effort will also contribute to the development of techniques for determining the influence of past and future emissions reductions on ambient concentrations of O3 as well as other pollutants.