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Airborne measurements of the spatial distribution of aerosol chemical composition across Europe and evolution of the organic fraction

By W Morgan, J Allan, K Bower, Eleanor Jo Highwood, D Liu, G McMeeking, Megan Northway, P Williams, R Krejci and H Coe

Abstract

The spatial distribution of aerosol chemical composition and the \ud evolution of the Organic Aerosol (OA) fraction is investigated based \ud upon airborne measurements of aerosol chemical composition in the \ud planetary boundary layer across Europe. Sub-micron aerosol chemical \ud composition was measured using a compact Time-of-Flight Aerosol Mass \ud Spectrometer (cToF-AMS). A range of sampling conditions were evaluated, \ud including relatively clean background conditions, polluted conditions in \ud North-Western Europe and the near-field to far-field outflow from such \ud conditions. Ammonium nitrate and OA were found to be the dominant \ud chemical components of the sub-micron aerosol burden, with mass \ud fractions ranging from 20--50% each. Ammonium nitrate was found to \ud dominate in North-Western Europe during episodes of high pollution, \ud reflecting the enhanced NO_x and ammonia sources in this region. OA was \ud ubiquitous across Europe and concentrations generally exceeded sulphate \ud by 30--160%. A factor analysis of the OA burden was performed in order \ud to probe the evolution across this large range of spatial and temporal \ud scales. Two separate Oxygenated Organic Aerosol (OOA) components were \ud identified; one representing an aged-OOA, termed Low Volatility-OOA and \ud another representing fresher-OOA, termed Semi Volatile-OOA on the basis \ud of their mass spectral similarity to previous studies. The factors \ud derived from different flights were not chemically the same but rather \ud reflect the range of OA composition sampled during a particular flight. \ud Significant chemical processing of the OA was observed downwind of major \ud sources in North-Western Europe, with the LV-OOA component becoming \ud increasingly dominant as the distance from source and photochemical \ud processing increased. The measurements suggest that the aging of OA can \ud be viewed as a continuum, with a progression from a less oxidised, \ud semi-volatile component to a highly oxidised, less-volatile component. \ud Substantial amounts of pollution were observed far downwind of \ud continental Europe, with OA and ammonium nitrate being the major \ud constituents of the sub-micron aerosol burden. Such anthropogenically \ud perturbed air masses can significantly perturb regional climate far \ud downwind of major source regions

Publisher: Copernicus Publications
Year: 2010
OAI identifier: oai:centaur.reading.ac.uk:5860

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