HR: 08:00h
AN: A21G-01 INVITED    [Abstracts]
TI: Radical production as a controlling factor for oxidant fields and secondary organic aerosol production in the polluted atmosphere
AU: * Volkamer, R
EM: rainer.volkamer@colorado.edu
AF: University of Colorado at Boulder, UCB 215, Boulder, CO 80309-0215, United States
AU: Sheehy, P M
AF: MCE2, 3262 Holiday Ct. Suite 201, La Jolla, CA 92037, United States
AU: Molina, L
AF: MCE2, 3262 Holiday Ct. Suite 201, La Jolla, CA 92037, United States
AU: Molina, M J
AF: University of California San Diego, 9500 Gilman Drive MC0356, La Jolla, CA 92093, United States
AB: Recent field studies indicate that the gas-phase processing of primary VOCs, followed by condensation and reactive uptake of reaction products to aerosols is largely responsible for the high portion of organic aerosol mass in the Mexico City Metropolitan Area. The sources of the extremely fast and larger than expected formation of secondary organic aerosol are presently not clear, and could indicate missing SOA precursor VOCs or missing processes of SOA formation in current models. An additional uncertainty arises from our incapacity to adequately predict oxidant fields, in particular in the high NOx regime typical for morning hours, when observed levels of OH and HO2 radicals are inconsistent with our current understanding of HOx chemical cycles. Recent experimental and modeling evidence indicates that the processing of pollutants in the MCMA is NOx suppressed, and VOC limited, at different times of day. Chemical processing of primary VOCs in either of these chemical regimes is limited by the production of radicals. The oxidative capacity of the MCMA is being assessed in terms of the driving factors for OH, HO2 and RO2 radical production, as well as the recycling of radicals via the ROx cycle inside the city. Experimentally constrained model predictions indicate that the production of semivolatile VOC oxidation products due to uncertainties in our understanding of gas-phase radical processes adds significantly to the uncertainty in predicting SOA.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0322 Constituent sources and sinks
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting