Quantifying the sources of smog and regional haze in southeastern U.S.
M. Talat Odman, Georgia Institute of Technology, Atlanta, GA; and Y. Hu, A. G. Russell, and J. W. Boylan
Visibility Improvement – State and Tribal Association of the Southeast (VISTAS) is conducting a modeling study with the goal of lowering particulate matter (PM) levels and improving visibility in Southeastern United States. As part of that study, we conducted a detailed sensitivity analysis to quantify the contributions of various emission sources to smog and regional haze. For this purpose, we used the Community Multiscale Air Quality (CMAQ) model with emission projections for the year 2009 and conducted close to 100 sensitivity runs. In each run, emissions from a particular source category in a certain geographic area were reduced by 30% and responses of ozone and PM concentrations as well as light extinctions to these reductions were calculated.
The resolution of the grid was 12-km over the modeling domain whose boundary conditions were provided by prior 36-km modeling over the continental U.S. Two meteorological periods, one summer (June 1 – July 10, 2002) and one winter (November 19 – December 19, 2002), were simulated to capture the seasonal variation of the responses. Source categories to be analyzed were determined based on the results of our prior analyses for PM that showed the greatest impact from SO2 emissions followed by primary carbon (PC) emissions. For ozone, they include the usual suspects, i.e., NOx and VOC. Responses were calculated for the entire domain and visualized but decisions were made based on responses at national park and wilderness (Class 1) areas of the region as well as ozone and fine PM (i.e., PM2.5) non-attainment areas.
SO2 emission reduction is the most effective control strategy in reducing summertime PM2.5 levels whose largest component is sulfate and also the most beneficial strategy in improving visibility since sulfate is the largest summertime contributor to light extinction in the Southeast. The majority of worst visibility days in the region occur during summer, with the exception of a few coastal Class 1 areas that display worse visibility in winter. SO2 emissions also have an impact on ozone but this is generally very small. Electric generating utilities (EGU) are the single largest source of SO2 in the region. Controlling EGU emissions from 10 VISTAS states (Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee, Virginia and West Virginia) as well as the 3 neighboring regions (portions of Central, Midwest and Northeast regions that are within the modeling domain) was considered. At each Class 1 area visibility was affected at a different level by these reductions. The impacts of non-EGU point source SO2 emissions from the same geographic areas were also quantified. Controlling PC emissions from these 10 states and 3 regions were also considered as an alternative strategy to improve visibility. However the fire-related PC emissions were differentiated from the rest due to potential limitations in controlling these emissions. Finally, reducing NH3 emissions from the VISTAS region as a whole and the 3 neighboring regions were considered. In winter, NH3 reduction is the most effective strategy resulting in large reductions in nitrate and ammonium.
To quantify the sources of ozone, first NOx sources were classified as ground-level and elevated sources. Then, responses to NOx emission reductions from ground-level and, separately, from elevated sources of each individual VISTAS state and surrounding region were calculated. Finally, the impacts of domain-wide VOC reductions from biogenic and anthropogenic sources were quantified. These results will help the development of specific emission control strategies for future attainment of the national ambient air quality standards by the VISTAS states..
Session 5, Regional/Meso Scale Dispersion and Air Quality
Wednesday, 1 February 2006, 1:30 PM-4:45 PM, A407
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