Investigating a two-component model of solid fuel organic aerosol in London: processes, PM1 contributions, and seasonality

摘要

Solid fuel emissions, including those from biomass burning, are increasing inurban areas across the European Union due to rising energy costs andgovernment incentives to use renewable energy sources for heating. In orderto help protect human health as well as to improve air quality and pollutionabatement strategies, the sources of combustion aerosols, theircontributions, and the processes they undergo need to be better understood. Ahigh-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) wastherefore deployed at an urban background site between January and February2012 to investigate solid fuel organic aerosols (SFOA) in London. Thevariability of SFOA was examined and the factors governing the split betweenthe two SFOA factors derived from Positive Matrix Factorisation (PMF) wereassessed. The concentrations of both factors were found to increase duringthe night and during cold periods, consistent with domestic space heatingactivities. The split between the two factors is likely governedpredominantly by differences in burn conditions where SFOA1 best representsmore efficient burns and SFOA2 best represents less efficient burns. Thedifferences in efficiency may be due to burner types or burn phase, forexample. Different fuel types and levels of atmospheric processing alsolikely contribute to the two factors. As the mass spectral profile of SFOA ishighly variable, the findings from this study may have implications forimproving future source apportionment and factorisation analyses.During the winter, SFOA was found to contribute 38% to the totalnon-refractory submicron organic aerosol (OA) mass, with similarcontributions from both SFOA factors (20% from SFOA1 and 18% fromSFOA2). A similar contribution of SFOA was derived for the same period from acompact time-of-flight AMS (cToF-AMS), which measured for a full calendaryear at the same site. The seasonality of SFOA was investigated using theyear-long data set where concentrations were greatest in the autumn andwinter. During the summer, SFOA contributed 11% to the organic fraction,where emissions resulted from different anthropogenic activities such asbarbecues and domestic garden wood burning. The significant contribution ofSFOA to total organic mass throughout the year suggests that the negativeeffects on health and air quality, as well as climate, are not just confinedto winter as exposure to these aerosols and the associated black carbon canalso occur during the summer, which may have significant implications forair-quality policies and mitigation strategies.