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Night-time radical chemistry during the TORCH campaign

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Publication details

JournalAtmospheric Environment
DatePublished - Jun 2009
Issue number20
Number of pages7
Pages (from-to)3220-3226
Original languageEnglish


We present one of the most comprehensive studies of night-time radical chemistry to date, from the Tropospheric ORganic CHemistry experiment (TORCH) in the summer of 2003. TORCH provided a wealth of measurements with which to study the oxidizing capacity of the atmosphere. The measurements provided input to a zero-dimensional box model which has been used to study night-time radical chemistry during the campaign. Average night-time predicted concentrations of OH (2.6 x 10(5) molecule cm(-3)), HO2 (2.9 x 10(7) molecule cm(-3)) and [HO2+Sigma RO2] radicals (2.2 x 10(8) molecule cm-3) were an order of magnitude smaller than those predicted during the daytime. The model under-predicted the night-time measurements of OH, HO2 and [HO2+Sigma RO2] radicals, on average by 41%, 16% and 8% respectively. Whilst the model captured the broad features of night-time radical behaviour, some of the specific features that were observed are hard to explain. A rate of radical production assessment was carried out for the whole campaign between the hours of 00:00 and 04:00. Whilst radical production was limited owing to the absence of photolytic reactions, production routes via the reactions of alkenes with 03 provided an effective night-time radical source. Nitrate radical concentrations were predicted to be 0.6 ppt on average with a peak of 18 ppt on August 9th during a polluted hear wave period. Overall, the nitrate radical contributes about a third of the total initiation via RO2, mostly through reaction with alkenes. (C) 2009 Elsevier Ltd. All rights reserved.

    Research areas

  • Hydroxyl radical, Nitrate radical, Night-time chemistry, Tropospheric modelling, MARINE BOUNDARY-LAYER, ATMOSPHERIC CHEMISTRY, PEROXY-RADICALS, NITRATE, OH, OZONE, RO2, HO2

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