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dc.contributor.authorSheehy, P. M.
dc.contributor.authorMolina, Luisa Tan
dc.contributor.authorMolina, Mario J.
dc.contributor.authorVolkamer, R. A.
dc.date.accessioned2011-07-29T19:49:15Z
dc.date.available2011-07-29T19:49:15Z
dc.date.issued2010-07
dc.date.submitted2010-07
dc.identifier.issn1680-7324
dc.identifier.issn1680-7316
dc.identifier.urihttp://hdl.handle.net/1721.1/64993
dc.description.abstractA box model using measurements from the Mexico City Metropolitan Area study in the spring of 2003 (MCMA-2003) is presented to study oxidative capacity (our ability to predict OH radicals) and ROx (ROx=OH+HO2+RO2+RO) radical cycling in a polluted (i.e., very high NOx=NO+NO2) atmosphere. Model simulations were performed using the Master Chemical Mechanism (MCMv3.1) constrained with 10 min averaged measurements of major radical sources (i.e., HCHO, HONO, O3, CHOCHO, etc.), radical sink precursors (i.e., NO, NO2, SO2, CO, and 102 volatile organic compounds (VOC)), meteorological parameters (temperature, pressure, water vapor concentration, dilution), and photolysis frequencies. Modeled HOx (=OH+HO2) concentrations compare favorably with measured concentrations for most of the day; however, the model under-predicts the concentrations of radicals in the early morning. This "missing reactivity" is highest during peak photochemical activity, and is least visible in a direct comparison of HOx radical concentrations. We conclude that the most likely scenario to reconcile model predictions with observations is the existence of a currently unidentified additional source for RO2 radicals, in combination with an additional sink for HO2 radicals that does not form OH. The true uncertainty due to "missing reactivity" is apparent in parameters like chain length. We present a first attempt to calculate chain length rigorously i.e., we define two parameters that account for atmospheric complexity, and are based on (1) radical initiation, n(OH), and (2) radical termination, ω. We find very high values of n(OH) in the early morning are incompatible with our current understanding of ROx termination routes. We also observe missing reactivity in the rate of ozone production (P(O3)). For example, the integral amount of ozone produced could be under-predicted by a factor of two. We argue that this uncertainty is partly accounted for in lumped chemical codes that are optimized to predict ozone concentrations; however, these codes do not reflect the true uncertainty in oxidative capacity that is relevant to other aspects of air quality management, such as the formation of secondary organic aerosol (SOA). Our analysis highlights that apart from uncertainties in emissions, and meteorology, there is an additional major uncertainty in chemical mechanisms that affects our ability to predict ozone and SOA formation with confidence.en_US
dc.description.sponsorshipNational Science Foundation (U.S.) (ATM-0528227)en_US
dc.description.sponsorshipUnited States. Dept. of Energy (Grant DE-FG02-0563980)en_US
dc.description.sponsorshipAlliance for Global Sustainabilityen_US
dc.description.sponsorshipHenry & Camille Dreyfus Foundationen_US
dc.description.sponsorshipAlexander von Humboldt-Stiftungen_US
dc.description.sponsorshipNational Science Foundation (U.S.) (CAREER award ATM-0847793)en_US
dc.language.isoen_US
dc.publisherCopernicus Publications on behalf of the European Geosciences Unionen_US
dc.relation.isversionofhttp://dx.doi.org/10.5194/acp-10-6993-2010en_US
dc.rightsCreative Commons Attribution 3.0en_US
dc.rights.urihttp://creativecommons.org/licenses/by/3.0en_US
dc.sourceCopernicusen_US
dc.titleOxidative capacity of the Mexico City atmosphere - Part 2: A ROx radical cycling perspectiveen_US
dc.typeArticleen_US
dc.identifier.citationSheehy, P. M. et al. “Oxidative Capacity of the Mexico City Atmosphere – Part 2: A ROx Radical Cycling Perspective.” Atmospheric Chemistry and Physics 10.14 (2010) : 6993-7008.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciencesen_US
dc.contributor.approverMolina, Luisa Tan
dc.contributor.mitauthorMolina, Luisa Tan
dc.contributor.mitauthorMolina, Mario J.
dc.contributor.mitauthorVolkamer, R.
dc.contributor.mitauthorSheehy, P. M.
dc.relation.journalAtmospheric Chemistry and Physicsen_US
dc.eprint.versionFinal published versionen_US
dc.type.urihttp://purl.org/eprint/type/JournalArticleen_US
eprint.statushttp://purl.org/eprint/status/PeerRevieweden_US
dspace.orderedauthorsSheehy, P. M.; Volkamer, R.; Molina, L. T.; Molina, M. J.en
dc.identifier.orcidhttps://orcid.org/0000-0002-3596-5334
dc.identifier.orcidhttps://orcid.org/0000-0003-2339-3225
mit.licensePUBLISHER_CCen_US
mit.metadata.statusComplete


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