Sources of water-soluble organic carbon in fine particles at a southern European urban background site

Abstract

In this study, the temporal evolution and sources of water-soluble organic carbon (WSOC) in submicron particles at an urban background site in Elche (Spain) were investigated. Measurements of PM1 (N = 200) were carried out over one year (2021). Samples were analysed for organic carbon (OC), elemental carbon (EC), WSOC, levoglucosan, elements and major ions. A positive matrix factorization (PMF) analysis was performed in order to identify the sources of WSOC on an annual and a monthly basis. During the study period, traffic restrictions due to COVID-19 led to lower concentrations of PM1 and carbonaceous compounds than expected. The WSOC annual average mass concentration was 0.95 μg⋅m−3, with maximum values during the colder months. The apportionment results indicate that the biomass burning (BB) source contributed 30.63% to WSOC levels, road traffic (RT) accounted for 23.90% of the WSOC, while the contribution of a source related to secondary organic aerosol formation (ammonium sulfate-AS) was 33.80%. Minor sources of WSOC were: soil dust (SD) and secondary nitrate (SN), which contributed 7.44% and 4.22%, respectively, to WSOC concentrations. The WSOC/OC ratio did not exhibit significant variations during the study period, since source contributions were similar for WSOC and OC. The highest values of this ratio were recorded in summer, due to the higher contribution from the AS source to WSOC concentrations.