Estimation of emission adjustments from the application of four-dimensional data assimilation to photochemical air quality modeling

Four-dimensional data assimilation applied to photochemical air quality modeling is used to suggest adjustments to the emissions inventory of the Atlanta, Georgia metropolitan area. In this approach, a three-dimensional air quality model, coupled with direct sensitivity analysis, develops spatially and temporally varying concentration and sensitivity fields that account for chemical and physical processing, and receptor analysis is used to adjust source strengths. Proposed changes to domain-wide NOx, volatile organic compounds (VOCs) and CO emissions from anthropogenic sources and for VOC emissions from biogenic sources were estimated, as well as modifications to sources based on their spatial location turban vs, rural areas). In general, domain-wide anthropogenic VOC emissions were increased approximately two times their base case level to best match observations, domain-wide anthropogenic NOx and biogenic VOC emissions (BEIS2 estimates) remained close to their base case value and domain-wide CO emissions were decreased. Adjustments for anthropogenic NOx emissions increased their level of uncertainty when adjustments were computed for mobile and area sources (or urban and rural sources) separately, due in part to the poor spatial resolution of the observation field of nitrogen-containing species. Estimated changes to CO emissions also suffer from poor spatial resolution of the measurements. Results suggest that rural anthropogenic VOC emissions appear to be severely underpredicted. The FDDA approach was also used to investigate the speciation profiles of VOC emissions, and results warrant revision of these profiles. In general, the results obtained here are consistent with what are viewed as the current deficiencies in emissions inventories as derived by other top-down techniques, such as tunnel studies and analysis of ambient measurements. (C) 2001 Elsevier Science Ltd. All rights reserved.