Aircraft observations of the lower troposphere above a megacity: Alkyl nitrate and ozone chemistry

Aruffo, Eleonora, Di Carlo, Piero, Dari-Salisburgo, Cesare, Biancofiore, Fabio, Giammaria, Franco, Busilacchio, Marcella, Lee, James, Moller, Sarah, Hopkins, James, Punjabi, Shalini, Bauguitte, Stéphane, O'Sullivan, Debbie, Percival, Carl, Le Breton, Michael, Muller, Jennifer, Jones, Rod, Forster, Grant, Reeves, Claire ORCID:, Heard, Dwayne, Walker, Hannah, Ingham, Trevor, Vaughan, Stewart and Stone, Daniel (2014) Aircraft observations of the lower troposphere above a megacity: Alkyl nitrate and ozone chemistry. Atmospheric Environment, 94. pp. 479-488. ISSN 1352-2310

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Within the framework of the RONOCO (ROle of Nighttime chemistry in controlling the Oxidising Capacity of the atmOsphere) campaign a daytime flight over the metropolitan area of London were carried out to study the nitrogen oxide chemistry and its role in the production and loss of ozone (O) and alkyl and multifunctional nitrate (σANs). The FAAM BAe-146 aircraft, used for these observations, was equipped with instruments to measure the most relevant compounds that control the lower troposphere chemistry, including O, NO, NO, NO, NO, HNO, peroxy nitrates (σPNs), σANs, OH, and HO. In the London's flight a strong ozone titration process was observed when flying above Reading (downwind of London) and when intercepting the London plume. The coupled cycles of NO and HO can have different terminations forming σPNs, σANs, HNO or peroxides (HO, ROOH) altering the O production. In the observations reported here, we found that a strong ozone titration (δO=-16ppb), due to a rapid increase of NO (δNO=27ppb), corresponds also to a high increase of σANs concentrations (δσANs=3ppb), and quite stable concentrations of HNO and σPNs. Unexpectedly, compared with other megacities, the production of σANs is similar to that of O (O+NO), suggesting that in the London plume, at least during these observations, the formation of σANs effectively removes active NO and hence reduces the amount of O production. In fact, we found that the ratio between the ozone production and the alkyl nitrates production (observed) approximate the unity; on the contrary the calculated ratio is 7. In order to explain this discrepancy, we made sensitivity tests changing the alkyl nitrates branching ratio for some VOCs and we investigated the impact of the unmeasured VOCs during the flight, founding that the calculated ratio decreases from 7 to 2 and that, in this condition, the major contribution to the σANs production is given by Alkanes. Observations and analysis reported here suggest that in the London plume the high NO emissions and the chemistry of some VOCs (mainly Alkanes) produce high concentrations of σANs competing against the local ozone production.

Item Type: Article
Faculty \ School: Faculty of Science > School of Environmental Sciences
University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups: Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
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Depositing User: Pure Connector
Date Deposited: 25 Jul 2014 14:48
Last Modified: 13 Apr 2023 13:46
DOI: 10.1016/j.atmosenv.2014.05.040

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