HR: 16:00h
AN: A44B-01    [Abstracts]
TI: Regional scale modeling of particle nucleation in the lower atmosphere over the Eastern United States
AU: * Yu, F
EM: yfq@asrc.cestm.albany.edu
AF: Atmospheric Sciences Research Center, State University of New York at Albany, 251 Fuller Road, Albany, NY 12203 United States
AU: Xia, C
EM: chenxia@asrc.cestm.albany.edu
AF: Atmospheric Sciences Research Center, State University of New York at Albany, 251 Fuller Road, Albany, NY 12203 United States
AU: Demerjian, K L
EM: kld@asrc.cestm.albany.edu
AF: Atmospheric Sciences Research Center, State University of New York at Albany, 251 Fuller Road, Albany, NY 12203 United States
AB: It is well recognized that atmospheric particles affect regional air quality, human health, and climate, and these effects depend strongly on particle number size distributions and compositions. The number size distributions of atmospheric aerosols are determined by a number of microphysical processes, of which the nucleation process is critical but least understood. To understand the key microphysics controlling the formation and fate of secondary particles and to represent these processes in the models are important to improve the predictive understanding of the environmental and climatic impacts of atmospheric aerosols. In this study, we investigate the new particle formation in the lower continental atmosphere over the Eastern United States, using a nucleation sub-model coupled with the Comprehensive Air Quality Model with extensions (CAMx). The evolution of freshly formed particles at selected locations is also simulated with a detailed aerosol microphysics model driven by the time-dependent variables predicted with the CAMx. Our nucleation sub-model includes three different nucleation mechanisms: binary homogeneous nucleation (BHN) of H$_{2}$SO$_{4}$-H$_{2}$O, ternary homogeneous nucleation (THN) of H$_{2}$SO$_{4}$-H$_{2}$O-NH$_{3}$, and ion-mediated nucleation (IMN) of H$_{2}$SO$_{4}$-H$_{2}$O. The CAMx is driven by the meteorological fields from the meteorological model and uses the gridded emission inventory prepared with Sparse Matrix Operator Kernel Emissions (SMOKE) Modeling System. We find that the temporal and spatial variations of nucleation rates predicted by different nucleation theories are quite different. BHN theory predicts negligible nucleation in the lower atmosphere over Eastern United States. Based on the IMN theory, the plumes from Ohio River Valley and some urban centers are significant source of secondary particles. In such plumes, though the pre-existing particle concentration is high, the high production rate of H$_{2}$SO$_{4}$ as a result of high SO$_{2}$ concentration leads to relative high H$_{2}$SO$_{4}$(g) concentration which promotes nucleation. The IMN rates are limited by ionization rates (up to 20 ions cm$^{-3}$s$^{-1}$ in continental boundary layer). The nucleation rates predicted with the THN theory depend strongly on ammonia concentration and THN rates frequently exceed 10$^{6}$ cm$^{-3}$s$^{-1}$ in the regions with high NH3 concentration. The frequency and nucleation rates predicted with the IMN theory are consistent with the results from the Pittsburgh Air Quality Study (from July 2001 to June 2002) which indicate that nucleation occurred on 50% of the study days and the average nucleation rates during the nucleation periods never exceeded ~10 cm$^{-3}$s$^{-1}$. The power plant plumes frequently across Pittsburgh area, and in sunny days the IMN theory predicts significant nucleation in such plumes. In our simulations of the evolution of particle number size distributions, the condensation of precursor gases (including sulfuric acid and condensable organic species from both anthropogenic and biogenic sources) and the coagulation scavenging are taken into account. Our simulations indicate that a significant fraction of the freshly formed particles can grow to the sizes in the range of 30-100 nm within 10 hours. These particles may contribute to the regional haze formation and may serve as cloud condensation nuclei.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0345 Pollution--urban and regional (0305)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting