Abstract
Abstract. For the first time, the behaviour of non-refractory inorganic and organic submicron particulate through an entire annual cycle is investigated using measurements from an Aerodyne compact time-of-flight aerosol mass spectrometer (cToF-AMS) located at a UK urban background site in North Kensington, London. We show that secondary aerosols account for a significant fraction of the submicron aerosol burden and that high concentration events are governed by different factors depending on season. Furthermore, we demonstrate that on an annual basis there is no variability in the extent of secondary organic aerosol (SOA) oxidation, as defined by the oxygen content, irrespective of amount. This result is surprising given the changes in precursor emissions and contributions as well as photochemical activity throughout the year; however it may make the characterisation of SOA in urban environments more straightforward than previously supposed. Organic species, nitrate, sulphate, ammonium, and chloride were measured during 2012 with average concentrations (±1 standard deviation) of 4.32 (±4.42), 2.74 (±5.00), 1.39 (±1.34), 1.30 (±1.52), and 0.15 (±0.24) μg m−3, contributing 44, 28, 14, 13, and 2 % to the total non-refractory submicron mass (NR-PM1) respectively. Components of the organic aerosol fraction are determined using positive matrix factorisation (PMF), in which five factors are identified and attributed as hydrocarbon-like OA (HOA), cooking OA (COA), solid fuel OA (SFOA), type 1 oxygenated OA (OOA1), and type 2 oxygenated OA (OOA2). OOA1 and OOA2 represent more and less oxygenated OA with average concentrations of 1.27 (±1.49) and 0.14 (±0.29) μg m−3 respectively, where OOA1 dominates the SOA fraction (90%). Diurnal, monthly, and seasonal trends are observed in all organic and inorganic species due to meteorological conditions, specific nature of the aerosols, and availability of precursors. Regional and transboundary pollution as well as other individual pollution events influence London's total submicron aerosol burden. High concentrations of non-refractory submicron aerosols in London are governed by particulate emissions in winter, especially nitrate and SFOA, whereas SOA formation drives the high concentrations during the summer. The findings from this work could have significant implications for modelling of urban air pollution as well as for the effects of atmospheric aerosols on health and climate.
Highlights
Atmospheric aerosols have adverse effects on human health (Pope and Dockery, 2006), air quality (AQEG, 2012), visibility (Watson, 2002), and climate (Boucher et al, 2013)
Several high nitrate concentration events occurred throughout the year, which were the result of a combination of ambient conditions, availability of precursors, and air mass trajectory
Sulphate concentrations in London are predominantly influenced by regional pollution with few or no local sources and ammonium concentrations are governed by the availability of precursor emissions and meteorological conditions
Summary
Atmospheric aerosols have adverse effects on human health (Pope and Dockery, 2006), air quality (AQEG, 2012), visibility (Watson, 2002), and climate (Boucher et al, 2013). Previous studies highlight the variability in the contribution of both secondary inorganic and organic aerosol (SIA and SOA respectively) to the total mass depending on location (Jimenez et al, 2009). Additional variability of SOA sources and formation results from the long distances over which SOA precursors and the resulting aerosols can be transported as well as dependency on meteorological conditions (Martin et al, 2011). 3, an overview of the bulk non-refractory PM1 (NR-PM1) components including average mass, diurnal profiles, and seasonality is presented along with a discussion on the factors governing concentrations and temporal trends. 5, the organic components are identified and the results from the previous sections are used to probe the behaviour of urban SOA including temporal trends
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