title: Simplification of the representation of the organic component of atmospheric particulates.
abstract: We present an analysis of recent field data to investigate the variation in the organic component of atmospheric aerosol and its behaviour in the moist environment. In all locations the degree of oxygenation of the organic material increases with photochemical age, as does the particulate hygroscopicity. These changes will generally occur in spatial scales comparable to a single cell in global models at representative boundary layer wind speeds. Using ADDEM, a new model of the equilibrium state of multicomponent aerosol, we show that inorganic component changes must be responsible for the increase in particulate hygroscopicity with photochemical age. It is suggested that a common representation of nearfield and background organic aerosol composition is sufficient to describe the behaviour of organic components in a variety of field experiments; nearfield small mode organics being dominated by a combustion-derived unoxidised signature, whilst the background accumulation mode is more oxygenated and dominates in air masses with a photochemical age of more than a couple of days. This representation may be used within the sub-saturated regime to predict the behaviour of ambient particulates in the moist atmosphere. Whether a similar common representation can be used for cloud activation prediction in supersaturated environments, or for investigation of gas-to-particle partitioning, should be investigated.
authors.affiliation: Atmospheric Science Group, University of Manchester, PO Box 88, Sackville Street, Manchester, UK, M60 1QD.
authors.forename: Gordon
authors.initials: G
authors.lastname: McFiggans
authors.forename: M Rami
authors.initials: MR
authors.lastname: Alfarra
authors.forename: James
authors.initials: J
authors.lastname: Allan
authors.forename: Keith
authors.initials: K
authors.lastname: Bower
authors.forename: Hugh
authors.initials: H
authors.lastname: Coe
authors.forename: Mike
authors.initials: M
authors.lastname: Cubison
authors.forename: Dave
authors.initials: D
authors.lastname: Topping
authors.forename: Paul
authors.initials: P
authors.lastname: Williams
authors.forename: Stefano
authors.initials: S
authors.lastname: Decesari
authors.forename: Cristina
authors.initials: C
authors.lastname: Facchini
authors.forename: Sandro
authors.initials: S
authors.lastname: Fuzzi
mesh_terms: D000336:Aerosols / Q000032:analysis; D000393:Air Pollutants / Q000032:analysis*; D001272:Atmosphere / Q000032:analysis / Q000737:chemistry*; D004784:Environmental Monitoring / Q000379:methods*; D005843:Geography; D017745:Incineration; D007287:Inorganic Chemicals / Q000032:analysis; D009930:Organic Chemicals / Q000032:analysis*; D010083:Oxidants, Photochemical / Q000032:analysis; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D013816:Thermodynamics; D014919:Wind
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D007287:Inorganic Chemicals; D009930:Organic Chemicals; D010083:Oxidants, Photochemical; D010100:Oxygen