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| Titel |
Understanding in-situ ozone production in the summertime through radical observations and modelling studies during the Clean air for London project |
| VerfasserIn |
Lisa Whalley, Daniel Stone, Dwayne Heard, James Hopkins, Rachel Dunmore, James Lee, Jacqueline Hamilton, Alistair Lewis |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250151176
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| Publikation (Nr.) |
 EGU/EGU2017-15733.pdf |
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| Zusammenfassung |
| Understanding the chemistry of free-radicals in the urban atmosphere is necessary to understand the lifetime of primary pollutants and the production of secondary pollutants, such as ozone and organic aerosol.
Here we will present measurements of OH, HO2, HO2* (HO2 plus a contribution from larger alkane/alkene/aromatic related RO2) and total RO2 radicals taken during the ClearfLo campaign in central London in the summertime. A photostationary steady state (PSS) calculation of OH which considers measured OH reactivity as the sink term and the measured OH sources (of which HO2+NO reaction and HONO photolysis dominates) compares well with the observed levels of OH. Comparison with calculations from a detailed box model utilising the Master Chemical Mechanism v3.2, however, highlights a substantial discrepancy between radical observations under lower NOx conditions ([NO] < 2 ppbv) typically experienced during the afternoon hours and indicated that the model was missing a significant peroxy radical sink. Under elevated NOx conditions ([NO] > 5 ppbv) the model and measurements were in much better agreement. Known radical termination steps, such as HO2 uptake on aerosols, are not sufficient to reconcile the model measurement discrepancies alone and a PSS calculation of total RO2 highlights that part of the discrepancy is caused by missing sinks for the higher peroxy radical species. This missing sink is most evident when the air reaching the site had previously passed over central London to the East and when elevated temperatures were experienced. We postulate that uncertainties in the degradation mechanism of complex biogenic and diesel related VOC species which were particularly elevated and dominated OH reactivity under these easterly flows, may account for the model measurement disagreement. This model uncertainty leads to significantly more ozone production predicted using modelled peroxy radical concentrations vs ozone production from peroxy radicals measured at times when NO concentrations are low. |
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