The inclusion of photochemical initial concentrations in the combined-phase source apportionment of PM2.5, PAHs and VOCs from an industrialized environment

PM_2.5 species, PAHs and VOCs were sampled between 2013 and 2019 once every three or six days for a period of 24 hours in an industrialized city in Ontario, Canada, and analyzed to apportion their common sources. The consequences of using these species jointly for receptor modelling were assessed via combined-phase source apportionment that used the data as is, and in an approach that considered the potential for photochemical losses of gas-phase species. Thus, initial concentrations corrected for photochemistry, called PIC were calculated. The data were then analyzed either with positive matrix factorization or its dispersion-normalized variant (DN-PMF). Comparisons of applying PMF to the originally observed input data (BASE) and DN-PMF on data with PIC corrections were made. When the combined phase input data were analyzed, nine factors were resolved for both BASE and DN-PIC PMF. These factors were: particulate sulphate, secondary organic aerosol (SOA), particulate nitrate (pNO3), biomass burning with natural gas, crustal matter, winter blend of gasoline, coking/coal combustion, steelmaking, and summer blend/light duty vehicular emissions. On comparison of the BASE and DN-PIC PMF results, the average PM mass contribution of the summer gasoline fuel factor increased from 2% in BASE case to 5%, suggesting severe underestimation of this source’s initial contributions without DN-PIC. Also, substantial increases of reactive VOCs in the SOA factor, and PAHs with ≥four rings in the pNO3 and steelmaking factors were observed with DN-PIC PMF compared to the BASE PMF case, indicating that for the SOA factor, reactive VOCs at the location of study contributed to its sources.