Sulphuric acid and aerosol particle production in the vicinity of an oil refinery

In this paper we introduce in-situ observations of trace gases, aerosol particles and their precursors in the vicinity of an oil refinery and industrial area in Kilpilahti, Southern Finland. We conducted a one-month measurement campaign near the oil refinery during summertime when the sulphur dioxide concentrations at the site are typically the highest. The source areas around the measurement location were divided into three sectors: oil refinery area, industrial area and non-industrial area. The atmospheric concentrations of aerosols and trace gases showed a large temporal variability, when exposed to the different source areas. The median sulphur dioxide concentrations for the oil refinery, industrial and non-industrial area were 1.88 ppbv, 0.75 ppbv and 0.38 ppbv, respectively, and the corresponding sulphuric acid concentrations were 11.5 × 106 molecules/cm3, 4.4 × 106 molecules/cm3 and 1.3 × 106 molecules/cm3. The observed concentrations were similar to what have been measured in urban or industrial sites. The ratio between sulphuric acid and sulphur dioxide was the highest when the air mass was coming from the oil refinery. The correlation between the sulphuric acid and 1-2 nm particle concentrations was significant, but the composition of the particles remained unknown as no neutral sulphuric acid clusters were detected with the mass spectrometer. Only a few new particle formation events were observed during the measurement period, and during these events a large fraction of the particle growth could be explained by sulphuric acid condensation.