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DIAGNOSTIC MODEL EVALUATION FOR CARBONACEOUS PM 2.5 USING ORGANIC MARKERS MEASURED IN THE SOUTHEASTERN U.S.
Citation:
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).
Impact/Purpose:
The objectives of this task are to continue development and improvement of EPA's mesoscale (regional through urban scale) air quality modeling systems, such as the Community Multiscale Air Quality (CMAQ) model, as air quality management and NAAQS implementation tools. This task focuses on needed research and development of air quality models targeted for a major CMAQ model release in FY08. Model development for a broad scope of application is envisioned. For example, CMAQ will need to be able to simulate air quality feedbacks to meteorology and climate as well as intercontinental transport. The 2008 release of CMAQ is timed to coincide with EPA/OAR's and the states' needs for an improved model for assessments of progress (mid-course corrections) in the post-SIP submittal timeframe.
Description:
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.