HR: 11:05h
AN: A12C-04    [Abstracts]
TI: Evaluation of New Secondary Organic Aerosol Formation Models Based on Mexico City Field Measurements
AU: Dzepina, K
EM: katja.dzepina@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: * Jimenez, J L
EM: jose.jimenez@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: Volkamer, R
EM: rainer.volkamer@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: Aiken, A
EM: allison.aiken@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AU: Huffman, J A
EM: alex.huffman@colorado.edu
AF: University of Colorado-Boulder, UCB 216, Boulder, CO 80309-0216, United States
AB: Recent field studies have found large discrepancies in the measured vs. modeled SOA mass loadings in both urban and regional polluted atmospheres [Volkamer et al., 2006 and references therein]. The reasons for these large differences are unclear. Here we revisit the SOA formation measurements from Mexico City described by Volkamer et al. and compared them to very recently published SOA formation models, including the updated aromatic SOA yields of Ng et al. (2007), the formation of SOA from primary semivolatile and intermediate volatility species (SVOCs and IVOCs) proposed by Robinson et al. (2007), the lack of partitioning of SOA in POA surrogates (Zaveri et al., 2007), and the formation of SOA from glyoxal (Volkamer et al., 2007). Traditional SOA precursors (mainly aromatics) still fail to produce enough SOA to match the observations by a large factor. The low-NOx aromatic pathways of Ng. et al., which have higher SOA yields, make a very small contribution in this urban environment as the RO2 + NO reaction dominates the fate of the RO2 radicals. Glyoxal makes a significant contribution to SOA formation, with similar timing and oxygen-to-carbon ratio (O/C) as the measurements. SVOCs and IVOCs introduce a large amount of carbon that was not in models before, and which has a high SOA yield. With the parameters presented by Robinson et al., this mechanism can close the gap in SOA mass between measurements and models in our case studies. However the O/C ratio of the SOA produced by this mechanism is too low when compared with observations, and the timing of formation is also slightly delayed with respect to the observations, due to the need for several generations of oxidation to bring a significant fraction of the SVOCs and IVOCs into the particle phase. Much experimental work is needed for a realistic assessment of the importance, and for constraining of the parameters, of the Robinson mechanism, especially of the real concentrations and volatility distribution of SVOCs and IVOCs in urban air, but also of the reaction rates, oxygen gain upon oxidation, and activity coefficients. The sensitivities of the model to the various uncertain parameters are evaluated. The volatility of the model SOA is compared to field measurements using a thermal denuder. Finally the evaporation upon dilution and the evolution of the SOA after 3 more days of oxidation are evaluated.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting