Secondary organic carbon in different atmospheric environments of a continental region and seasons

Abstract

Secondary organic carbon (SOC) was derived using elemental carbon (EC) tracer method for primary organic carbon (OC) in daily aerosol samples collected in the regional background environment, suburban area, and central part of Budapest in each season. The estimation approaches of the OC/EC ratio for the major emission sources required for the tracer method were discussed, and the high EC edge approach was adopted separately for each location and season. The annual mean SOC concentrations in the environments listed were 1.16, 1.51 and 1.42 μg m−3, respectively. They were interpreted together with the PM2.5 mass, OC, EC, water-soluble OC (WSOC), levoglucosan (LVG) and meteorological variables. The annual mean contributions of SOC to OC were 45% at all sampling sites. However, they showed substantial seasonal variation at each location. The shares were the smallest (<≈30%) in winter, whereas they prevailed in summer (in the regional background, this even reached 66%). The secondary organic aerosol (obtained by multiplying the SOC concentrations by the organic mass-to-OC correction factor) made up roughly 25% of the PM2.5 mass except for winter, when it was 10%. Obvious associations of the SOC on the one side and PM2.5 mass, OC and WSOC on the other side were identified as joint relationships for all seasons. The SOC correlated with LVG only in winter when the relative intensity of biomass burning is the highest, and with O3 only in spring and summer, when the role of photochemistry is considerable. Elevations in PM2.5 mass, OC and WSOC concentrations on a daily scale were related to the enhancement of SOC concentration by factors of 0.14, 0.4 and 0.6, respectively, while higher LVG levels in winter enlarged the SOC 3-times. There was a relationship between the SOC and OC from fossil fuel combustion over all seasons, whereas the dependency between the SOC and OC from biomass burning could be established only in winter, and between the SOC and OC from biogenic sources apart from winter. The results and conclusions have importance for the health consequences of SOC in cities and rural areas over the whole Carpathian Basin.