You are here:
PRIMARY AND SECONDARY ORGANIC AEROSOLS OVER THE UNITED STATES: ESTIMATES ON THE BASIS OF OBSERVED ORGANIC CARBON (OC) AND ELEMENTAL CARBON (EC), AND AIR QUALITY MODELED PRIMARY (OC/EC) RATIOS
Citation:
Yu, S., R L. Dennis, P. BHAVE, AND B K. Eder. PRIMARY AND SECONDARY ORGANIC AEROSOLS OVER THE UNITED STATES: ESTIMATES ON THE BASIS OF OBSERVED ORGANIC CARBON (OC) AND ELEMENTAL CARBON (EC), AND AIR QUALITY MODELED PRIMARY (OC/EC) RATIOS. ATMOSPHERIC ENVIRONMENT 38(31):5257-5268, (2004).
Impact/Purpose:
The goal of this task is to thoroughly characterize the performance of the emissions, meteorological and chemical/transport modeling components of the Models-3 system, with an emphasis on the chemical/transport model, CMAQ. Emissions-based models are composed of highly complex scientific hypotheses concerning natural processes that can be evaluated through comparison with observations, but not validated. Both performance and diagnostic evaluation together with sensitivity analyses are needed to establish credibility and build confidence within the client and scientific community in the simulations results for policy and scientific applications. The characterization of the performance of Models-3/CMAQ is also a tool for the model developers to identify aspects of the modeling system that require further improvement.
Description:
The temporal and spatial distributions of primary and secondary organic carbon aerosols (OC) over the continental US during June 15 to August 31, 1999, were estimated by using observational OC and elemental carbon (EC) data from Interagency Monitoring of Protected Visual Environments (IMPROVE) and Southeastern Aerosol Research and Characterization project (SEARCH) networks, coupled with the primary OC/EC ratios, (OC/EC)pri, obtained from an emission/transport-model (i.e., US EPA Models-3/Community Multiscale Air Quality (CMAQ) model). It was found that the mean primary OC concentrations over the Northeast, Southeast, Central, West and West Pacific regions were 0.39 +/-0.09 (mean standard deviation), 1.02 +/-0.55, 0.47+/- 0.34, 0.51+/-0.24, and 0.96 +/-0.68 ug C m-3, respectively, while the mean secondary OC concentrations were 1.27 +/-0.15, 1.52+/-0.59, 0.90+/- 0.51, 0.51+/- 0.29, and 0.94+/-0.52 ug C m-3, respectively. The contribution of secondary OC to the measured OC ranged from 48 +/-16% over the West to 77 +/-3% over the Northeast. The mean values of modeled (OC/EC)pri ratios ranged from 1.16 +/-0.13 over the Northeast to 3.49 +/-1.22 over the West Pacific. The results at the SEARCH sites indicate that the daily mean values of modeled (OC/EC)pri ratios ranged from 0.84 to 2.99 at Yorkville and the contributions of secondary OC to OC ranged from 0% to 66% at North Birmingham. Our results indicate significant temporal and geographic variability in the relative contributions of primary and secondary OC and that the use of a constant value to represent the (OC/EC)pri ratio at a location is not appropriate over the time scales studied here.
The United States Environmental Protection Agency through its Office of Research and Development funded and managed the research described here. It has been subjected to Agency's administrative review and approved for publication.
