BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:Interactions of HOx with aerosols\; Nitric acid-HONO-NOx cycling v ia particulate nitrate photolysis - Daniel Moon and Dr Chunxiang Ye\, Univ ersity of Leeds DTSTART:20161024T131500Z DTEND:20161024T141500Z UID:TALK68283@talks.cam.ac.uk CONTACT:Peter Gallimore DESCRIPTION:_Heterogeneous production and loss of HOx by airborne TiO2 par ticles and implications for climate change mitigation strategies and Heter ogeneous loss of HO2 from Cu-Fe redox coupling in inorganic salt aerosols - Daniel Moon_\n \nThe seminar presents findings from two laboratory studi es that both focus on heterogeneous reactions between HOx and aerosols. Th e first study investigates the heterogeneous reaction between airborne sub -micron TiO2 particles and HO2 radicals using an aerosol flow tube and the FAGE (fluorescence assay by gas expansion) technique. Experiments perfor med in dark conditions at the most stratospherically relevant conditions w ithin this study (RH = 11.1%) determined γHO2 = (2.08 ± 0.11) × 10-2. A positive dependence of γHO2 with RH was observed which showed a correlat ion between γHO2 and the number of monolayers of water adsorbed on the pa rticle surface. Modelling of stratospheric chemistry (TOMCAT) showed that uptake of HO2 by injected TiO2 aerosols would have a negligible effect to stratospheric concentrations of HO2 and O3. However\, when experiments wer e illuminated with near-UV light (365 nm) significant HO2 production was o bserved. This is the first time HO2 radicals from aerosols have been direc tly observed. The concentrations were dependent on light flux\, RH and tot al particle surface area. Work is still under-going to show its effect to stratospheric chemistry.\n\nSecondly\, conventionally the product of HO2 uptake by aerosols was thought to be H2O2\, however\, Mao (2013) proposed an alternative reaction mechanism where a fast electron transfer reaction between Cu(I) and Fe(III) occurs resulting in the production of H2O. This has important implications to atmospheric modelling as H2O2 is a far less efficient sink of HOx than H2O affecting predicted tropospheric concentra tions of OH\, O3\, CO and other species. This study investigates the heter ogeneous reaction between HO2 and (NH4)2SO4 aerosols doped with varying ra tios of Cu(II) and Fe(II) ions totalling in concentrations of 10-3 and 10- 4 M in the atomiser solution using an aerosol flow tube and FAGE. Results from the study show a significant enhancement of the uptake coefficient f rom what would be expected if the two ions were reacting in isolation as t he Cu(II)/Fe(II) mole fraction increases from 0 to 0.15 suggesting likely interaction between the two transition metal ions. Work is currently under way using the KM-SUB model to predict the uptake coefficient with the vary ing ratio of Cu(II) and Fe(II) ions using conventional reaction mechanisms and the reaction mechanism proposed by Mao to interpret results. \n \n_F ield\, laboratory and model evidences on cycling chemistry of particulate nitrate-HONO-NOx - Chunxiang Ye_\n \nNitrogen oxides are essential to the formation of secondary atmospheric aerosol and of atmospheric oxidants suc h as ozone and the hydroxyl radical\, which controls the self-cleansing ca pacity of the atmosphere. Nitric acid\, a major oxidation product of nitro gen oxides\, has traditionally been considered to be a permanent sink of n itrogen oxides. However\, model studies predict higher ratios of nitric ac id to nitrogen oxides in the troposphere than in observations. A 'renoxifi cation' process that recycles nitric acid into nitrogen oxides has been pr oposed to reconcile observations with model studies\, but the mechanisms r esponsible for this process remain uncertain. Here we present data from an aircraft measurement campaign in the North Atlantic Ocean and find eviden ces for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. La boratory experiments further demonstrate the photolysis of particulate nit rate collected on filters at a rate more than two orders of magnitude grea ter than that of gaseous nitric acid\, with nitrous acid as the main produ ct. Master Chemical Mechanism model calculations suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. \n LOCATION:Pfizer Lecture Theatre\, Department of Chemistry END:VEVENT END:VCALENDAR