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Size-segregated particle samples were collected using a Berner 5-stage impactor (stages 1-5: 0.05-0.14-0.42-1.2-3.5-10 μm aerodynamic diameter). The means for all 169 days and for different categories of days were used for a characterization. The sorting criteria were (a) the distinction between winter (Wi, November to April) and summer (Su, May to October), (b) the distinction between air mass inflow from a sector West (W, 210°-320°) and from a sector East (E, 35°-140°). For the assignment of the air mass origin 96-h backward trajectories were used and four categories (WiW, WiE, SuW and SuE) with 48, 18, 42 and 29 days were established. The lowest mean particle mass concentrations were found for SuW and the highest for WiE with relative mass concentration distributions of 5.9, 28.2, 36.5, 18.0, and 11.4 % and 3.5, 22.7, 52.6, 16.7, and 4.5 % for stages 1-5, respectively. The mass closure for water soluble ions, water, organic material (OM) and elemental carbon (EC) accounts for 81-99 % of the gravimetric mass in Wi and for 60-81 % for Su, depending on the stage. The fractions of nitrate were relatively high for WiW while sulphate fractions are high for WiE. The estimated concentrations of secondary organic carbon (SOA) on stage 3 for WiW, WiE, SuW and SuE were 0.32, 1.25, 0.27 and 0.58 μgm − ³, respectively. The highest amount of SOA is found for WiE, representing 59 % of organic carbon (OC). The highest difference in the percentages of SOA in OC was found between winter (WiW 55 %, WiE 59 %) and summer (SuW and SuE 74 %) indicating photochemical processes during long-range transport. The mean Carbon Preference Indices (CPI) are highest for SuE (stage 4: 7.57 and stage 5: 9.82) resulting mainly from plant wax abrasion in the surrounding forests. For WiE the mean PAH concentration on stage 3 (9.7 ngm −3 ) is about five times higher than for WiW, indicating long range transport following domestic heating and other combustion processes.

Abstract. In the course of two field campaigns, sizesegregated particle samples were collected at nine sites in Germany, including traffic, urban, rural, marine and mountain sites. During the chemical characterisation of the samples some of them were found to contain an unknown substance that was later identified as hydroxymethanesulfonic acid (HMSA). HMSA is known to be formed during the reaction of S(IV) (HSO − 3 or SO 2− 3 ) with formaldehyde in the aqueous phase. Due to its stability, HMSA can act as a reservoir species for S(IV) in the atmosphere and is therefore of interest for the understanding of atmospheric sulfur chemistry. However, no HMSA data are available for atmospheric particles from central Europe, and even on a worldwide scale data are scarce. Thus, the present study now provides a representative data set with detailed information on HMSA concentrations in size-segregated central European aerosol particles. HMSA mass concentrations in this data set were highly variable: HMSA was found in 224 out of 738 samples (30 %), sometimes in high mass concentrations exceeding those of oxalic acid. On average over all 154 impactor runs, 31.5 ng m −3 HMSA was found in PM 10 , contributing 0.21 % to the total mass. The results show that the particle diameter, the sampling location, the sampling season and the air mass origin impact the HMSA mass concentration. Highest concentrations were found in the particle fraction 0.42-1.2 µm, at urban sites, in winter and with eastern (continental) air masses, respectively. The results suggest that HMSA is formed during aging of pollution plumes. A positive correlation of HMSA with sulfate, oxalate and PM is found (R 2 > 0.4). The results furthermore suggest that the fraction of HMSA in PM slightly decreases with increasing pH.

Abstract. In the course of two field campaigns, size-segregated particle samples were collected at nine sites in Germany, including traffic, urban, rural, marine, and mountain sites. During the chemical characterisation of the samples some of them were found to contain an unknown substance that was later on identified as hydroxymethanesulfonic acid (HMSA). HMSA is known to be formed during the reaction of S(IV) (HSO3− or SO32−) with formaldehyde in the aqueous phase. Due to its stability, HMSA may can act as a reservoir species for S(IV) in the atmosphere and is therefore of interest for the understanding of atmospheric sulphur chemistry. However, no HMSA data are available for atmospheric particles from Central Europe and even on a worldwide scale, data are scarce. Thus, the present study now provides a representative dataset with detailed information on HMSA concentrations in size-segregated Central European aerosol particles. HMSA mass concentrations in this dataset were highly variable: HMSA was found in 224 out of 738 samples (30%), sometimes in high mass concentrations exceeding those of oxalic acid. In average over all 154 impactor runs, 31.5 ng m−3 HMSA were found in PM10, contributing 0.21% to the total mass. The results show that the particle diameter, the sampling location, the sampling season and the air mass origin impact the HMSA mass concentration. Highest concentrations were found in the particle fraction 0.42–1.2 μm, at urban sites, in winter and with eastern (continental) air masses, respectively. The results suggest that HMSA is formed during aging of pollution plumes. A positive correlation of HMSA with sulphate, oxalate and PM is found (R2 > 0.4). The results furthermore suggest that the fraction of HMSA in PM slightly decreases with increasing pH.

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