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- Title
The Impact of Isoprene Emissions on Air Quality in China.
- Authors
Liu, Yanhui; Reeves, Claire; Dorling, Stephen; Mills, Graham; Lee, James; Hopkins, James; Acton, Joe; Whalley, Lisa; Slater, Eloise; Langford, Ben; Nemitz, Eiko; Zhang, Qiang; Wu, Ruili
- Abstract
Isoprene, primarily emitted by vegetation, is considered to be the most important biogenicvolatile organic compound (BVOC) in the troposphere due to its abundant emission (∼40%of total VOCs globally) and high ozone (O3) formation potential. Once it is released to theatmosphere, isoprene is rapidly oxidised to form peroxy radicals (RO2), which can react withnitric oxide (NO) to form nitrogen dioxide (NO2), which when photolysed can form O3.However, a minor branch of the RO2 and NO reaction yields stable isoprene nitrates (INs)that temporarily terminate the O3 production by tying the active nitrogen into thenitrate functional group. The lifetimes of some of these nitrates are relatively long(days to weeks), so they can be transported and destroyed away from the source,releasing NO2 back to the atmosphere downwind. In other words, the formation of INscan change the O3 distribution. The role of INs in NOX (NO + NO2) recycling ispoorly understood, in part due to a lack of field measurement of the individualINs. Individual IN isomers derived through different isoprene initial-oxidation pathways (OHand NO3) were measured with a gas chromatography / mass spectrometry analytical systemin the summer of 2016 in Beijing as part of the Air Pollution and Human Health in aDeveloping Megacity (APHH-Beijing) programme. A regional chemistry transport model(Weather Research and Forecasting model coupled with Chemistry, WRF-Chem) has been setup to simulate the isoprene oxidation processes during the campaign period for most ofChina. Since existing chemical mechanisms coupled to WRF-Chem represent the INs aslumped organic nitrates, we developed a more explicit chemical mechanism with 7 INisomers by adding the Mainz Isoprene Mechanism (MIM2) and aspects of the MasterChemical Mechanism (MCM) to the Model for Ozone and Related chemical Tracers(MOZART-4) mechanism. The measurement data from Beijing have been used to evaluate and improve ourunderstanding of the production and loss of the INs. The modelled diel patterns of INsagree well with the observations, although there are discrepancies in the absoluteconcentrations. The impact of isoprene on O3, NOX, NOY and HOX in differentregimes across China is discussed in terms of the NOX-isoprene ratio as well as therole of isoprene derived organic nitrates in NOX recycling. The amount of NOXrecycled through the INs is quantified by using a tagging method. We also examinehow different treatments of isoprene and the INs in reduced mechanisms affect theresults, including the sensitivity of the formation of INs to the RO2 cross-reactions.
- Subjects
BEIJING (China); CHINA; ISOPRENE; PEROXY radicals; ACTIVE nitrogen; CHEMICAL models; AIR pollution; OZONIZATION; OZONE generators; AIR quality
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article