On the use of reference mass spectra for reducing uncertainty in source apportionment of solid fuel burning in ambient organic aerosol

Abstract. Reference mass spectra are routinely used to facilitate source apportionment of ambient organic aerosol (OA) measured by an aerosol chemical speciation monitor (ACSM). However. source apportionment of solid fuel burning emissions can be complicated by the use of different fuels, stoves and burning conditions. In this study, the organic aerosol mass spectra produced from burning a range of solid fuels in several stoves have been compared using an ACSM. The same samples of biomass briquettes and smokeless coal were burnt in a conventional and Ecodesign stove, while different batches of wood, peat, and smoky coal were also burnt in the conventional stove and the OA mass spectra compared to those previously obtained using a boiler stove. The results shows that although certain ions (e.g., m/z 60) remain important markers for solid fuel burning, the peak intensities obtained at specific m/z values were not constant with variations ranging from <5% to >100 %. Using the OA mass spectra of peat, wood and coal as anchoring profiles and the variation of individual m/z values for the upper/lower limits in ME-2 analysis (the limits approach), the respective contributions of these fuels to ambient sub-micron aerosols during a winter period in Dublin were evaluated and compared with the conventional a value approach. The ME-2 solution was stable for the limits approach with uncertainties in the range of 2–7 %, while relatively large uncertainties (8–29 %) were found for the a value approach. Nevertheless, both approaches showed good agreement overall, with the burning of peat (39 % vs 41 %) and wood (14 % vs 11 %) accounting for the majority of ambient organic aerosol during polluted evenings, despite their small uses. This study, thus, accounts for the source variability in ME-2 modelling and provides better constraints on the primary factor contributions to the ambient organic aerosol estimations. The finding from this study has significant implications for public health and policymakers considering that it is often the case that different batches of solid fuels are often burned in different stoves in real-world applications.