HR: 1330h
AN: A42A-0749    [PDF]
TI: Simulation of Coarse Particle Nitrate Formations in Coastal Areas Using CMAQ-AIM
AU: * Zhang, K M
EM: maxzhang@ucdavis.edu
AF: University of California, Department of Mechanical and Aeronautical Engineering, University of California, Davis, CA 95616 United States
AU: Dennis, R L
EM: dennis.robin@epamail.epa.gov
AF: National Oceanic and Atmospheric Administration, Atmospheric Sciences Modeling Division, National Oceanic and Atmospheric Administration, Air Resources Laboratory, RTP, NC 27711 United States
AU: Mebust, M R
EM: mmebust@hpcc.epa.gov
AF: National Oceanic and Atmospheric Administration, Atmospheric Sciences Modeling Division, National Oceanic and Atmospheric Administration, Air Resources Laboratory, RTP, NC 27711 United States
AU: Bhave, P V
EM: bhave.prakash@epa.gov
AF: National Oceanic and Atmospheric Administration, Atmospheric Sciences Modeling Division, National Oceanic and Atmospheric Administration, Air Resources Laboratory, RTP, NC 27711 United States
AU: Wexler, A S
EM: aswexler@ucdavis.edu
AF: University of California, Department of Mechanical and Aeronautical Engineering, Department of Civil and Environmental Engineering and Department of Land, Air, and Water Resources, University of California, Davis, CA 95616 United States
AB: The air quality model, CMAQ-AIM, was used to simulate the formation of coarse particle nitrate in coastal areas. CMAQ-AIM adopts USEPA's Models-3/CMAQ as the host photochemical model and employs a mechanistic, fully dynamic, internally-mixed, sectional aerosol module containing twelve aerosol species in nine size sections spanning 0.03 to 20 $\mu$m. The model's superior computational efficiency is achieved by a novel integration scheme and acid-neutrality gas-particle transport mechanisms, among which the Replacement Transport mechanism is particularly suitable for simulating the displacement of hydrochloric acid by nitric acid, or vice versa. The modeling results in Tampa Bay area from June 30 to July 14, 1999 episode (with sea-salt emission) in USEPA's Lower 49 State domain were compared to those produced by Models-3/CMAQ (without sea-salt emissions and a modal representation of the particulate matter). The preliminary comparison showed that total nitrate concentrations (gas and particle phase) were compatible between the two models, but CMAQ-AIM predicted a higher fraction of total nitrate partitioned into particle phase with over ninety percent of particle nitrate mass (about 1 $\mu$gm$^{-3}$) in the coarse mode, while fine particle nitrate mass was in the similar magnitude as accumulation mode particle nitrate simulated by Models-3/CMAQ. Due to CMAQ-AIM's ability to simulate sea salt and the displacement reaction, the importance of sea-salt emission in ambient air quality in coastal areas was demonstrated. Given that gas-phase nitrate deposition is usually reduced over water surface compared to that over land and coarse particle nitrate deposition remains unchanged, with high deposition velocity, our simulation indicates direct atmospheric particle nitrate deposition may significantly contribute to the total nitrate deposition into estuary habitats, which is consistent with BRACE measurement results. Since CMAQ-AIM also predicted coarse particle nitrate formation in many other coastal regions, our study suggests coarse mode nitrate needs to be measured in field campaigns in those areas; otherwise, a major fraction of total nitrate deposition would be missed.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0315 Biosphere/atmosphere interactions
DE: 0345 Pollution--urban and regional (0305)
DE: 4504 Air/sea interactions (0312)
DE: 4801 Aerosols (0305)
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting