Abstract. The seasonal variability of non-refractory PM1 (NR-PM1) was studied at a rural background site (National Atmospheric Observatory Košetice – NAOK) in the Czech Republic to examine the impact of atmospheric regional and long-range transport in Central Europe. NR-PM1 measurements were performed by compact time-of-flight aerosol mass spectrometry (C-ToF-AMS), and the chemically speciated mass size distributions, effective density, and origin were discussed. The average PM1 concentrations, calculated as the sum of the NR-PM1 (after collection efficiency corrections – CE corrections of 0.4 and 0.33 in summer and winter, respectively) and the equivalent black carbon (eBC) concentrations measured by an aethalometer (AE), were 8.58 ± 3.70 μg m−3 in summer and 10.08 ± 8.04 μg m−3 in winter. Organics dominated during both campaigns (summer/winter: 4.97 ± 2.92/4.55 ± 4.40 μg m−3), followed by sulphate in summer (1.68 ± 0.81/1.36± 1.38 μg m−3) and nitrate in winter (0.67 ± 0.38/2.03 ± 1.71 μg m−3). The accumulation mode dominated the average mass size distribution during both seasons, with larger particles of all species measured in winter (mode diameters: Org: 334/413 nm, NO3−: 377/501 nm, SO42−: 400/547 nm, and NH4+: 489/515 nm) pointing to regional and long-range transport. However, since the winter aerosols were less oxidized than the summer aerosols (comparing fragments f44 and f43), the importance of local sources in the cold part of the year was not negligible. The average PM1 particle effective density, defined as the ratio of the mass to the volume of a particle, corresponded to higher inorganic contents during both seasons (summer: ∼ 1.30 g cm−3 and winter: ∼ 1.40 g cm−3). However, the effective densities during episodes of higher mass concentrations calculated based on the particle number (mobility diameter) and mass size distribution (vacuum aerodynamic diameter) were even higher, ranging from 1.40–1.60 g cm−3 in summer and from 1.40–1.75 g cm−3 in winter. Although aged continental air masses from the SE were rare in summer (7 %), they were connected with the highest concentrations of all NR-PM1 species, especially sulphate and ammonium. In winter, slow continental air masses from the SW (44 %) were linked to inversion conditions over Central Europe and were associated with the highest concentrations among all NR-PM1 measurements.
Supplementary material to "Composition and mass size distribution of nitrated and oxygenated
aromatic compounds in ambient particulate matter from southern
and central Europe – implications for origin"
