Contributions from transport, solid fuel burning and cooking to primary organic aerosols in two UK cities

Abstract

Abstract. Organic matter frequently represents the single largest fraction of fine particulates in urban environments and yet the exact contributions from different sources and processes remain uncertain, owing in part to its substantial chemical complexity. Positive Matrix Factorisation (PMF) has recently proved to be a powerful tool for the purposes of source attribution and profiling when applied to ambient organic aerosol data from the Aerodyne Aerosol Mass Spectrometer (AMS). Here we present PMF analysis applied to AMS data from UK cities for the first time. Three datasets are analysed, with the focus on objectivity and consistency. The data were collected in London during the Regent's Park and Tower Environmental Experiment (REPARTEE) intensives and Manchester. These occurred during the autumn and wintertime, such that the primary fraction would be prominent. Ambiguities associated with rotationality within sets of potential solutions are explored and the most appropriate solution sets selected based on comparisons with external data. In addition to secondary organic aerosols, three candidate sources of primary organic aerosol (POA) were identified according to mass spectral and diurnal profiles; traffic emissions, cooking and solid fuel burning (for space heating). Traffic represented, on average, 40% of POA during colder conditions and exhibited a hydrocarbon-like mass spectrum similar to those previously reported. Cooking aerosols represented 34% of POA and through laboratory work, their profile was matched with that sampled from the heating of seed oils, rather than previously-published spectra derived from charbroiling. This suggests that in these locations, oil from frying may have contributed more to the particulate than the meat itself. Solid fuel aerosols represented 26% of POA during cold weather conditions but were not discernable during the first REPARTEE campaign, when conditions were warmer than the other campaigns. This factor showed features associated with biomass burning and occurred mainly at night. Grid-scale emission factors of the combustion aerosols suitable for use in chemical transport models were derived relative to CO and NOx. The traffic aerosols were found to be 20.5 μg m−3 ppm−1 relative to CO for Manchester and 31.6 μg m−3 ppm−1 relative to NOx for London. Solid fuel emissions were derived as 24.7 μg m−3 ppm−1 relative to CO for Manchester. These correspond to mass emission ratios of 0.018, 0.026 (as NO) and 0.021 respectively and are of a similar order to previously published estimates, derived from other regions or using other approaches.

Three-dimensional factorization of size-resolved organic aerosol mass spectra from Mexico City

“…These factors usually have similar mass spectra but different size distributions and time series (Fig. S6 in (Allan et al, 2010;, our solutions within the same family show less variation than in the reported 2-D cases. The variation among the solutions in each family is quite small.…”

“…We calculate each solution from 50 different starting seeds and then compare these solutions ). The 50 solutions can be grouped into "families" of solutions by comparing Q/Q exp values and the similarity of factors within the family (Allan et al, 2010;. Each family can then be represented by the average of the solutions in that family, and one family can be selected as the best solution.…”

Organic aerosol composition and sources in Pasadena, California, during the 2010 CalNex campaign

“…Shown in Figure 7b is a scatter plot of the CO and the HOA + CIOA data. The improved correlation when the CIOA mass concentration is added to the HOA mass concentration is surprising because cooking is not considered a major source of carbon monoxide, although it is a significant source of organic aerosol [Allan et al, 2010; California Air Resources Board, California emission inventory data, 2008, http://www.arb.ca.gov/ei/ emsmain/emsmain.htm; Harley et al, 1997]. Emissions of CO have been measured from certain cooking activities [Lee et al, 2001], but it is still a possibility that the CIOA component contains particulate mass from noncooking sources that also emit CO (e.g., gasoline vehicles).…”

Formation of secondary organic aerosol coating on black carbon particles near vehicular emissions

“…The results of PMF illustrate that rBC-and HOA-rich factors accounted for about 60 and 20 wt % of rBC with a thin coating, respectively, and the rBC-rich factor contributed about 82 wt % of the freshly emitted rBC from traffic, similar to previous observations in the roadside environment . The COA factor is commonly observed in urban areas (Allan et al, 2010;Mohr et al, 2012) but its mixing with ambient rBC is seldom reported. The absence of a COA factor in rBC-containing particles highlights the fact that emissions of rBC from modern kitchens and the mixing of rBC and COA through particle coalescence were negligible in this study.…”