This study investigated the PM1-2.5 (the intermodal fraction of particulate matter) representing the transition area between the fine and coarse size ranges. Due to this characteristic, PM1-2.5 may contain particles from both modes. The aim of this work was to examine the associations between PM1-2.5 and the coarse (PM2.5-10)/fine (PM1) fraction under different meteorological conditions at various sites in the Czech Republic during winter and summer.
Size-resolved PM mass concentrations were determined and meteorological parameters recorded at an urban industrial and a suburban site in Ostrava during winter 2014 and at an urban traffic site and a suburban site in Prague during summer 2014 and winter 2015. The influence of sources producing the coarse/fine fraction on PM1-2.5 was investigated with an elemental composition analysis and an ion analysis (Ca2+-representing PM2.5-10 and SO42–-representing PM1).
During all campaigns, PM1-2.5 accounted for 1–26% of PM10. In winter, crustal elements (Si, Fe, Si, Ca) significantly influenced the coarse fraction and even PM1-2.5 at all sites, while sulfur was significant in PM1-2.5 and the fine fraction at suburban sites. The median SO42– concentration was higher than the Ca2+ concentration in PM1-2.5 at all sites, except the industrial site, due to a specific source. The increased SO42– amount in PM1-2.5 was also observed in summer during rainy days (Prague urban site). In summer, crustal elements were important in both, PM1-2.5 and the coarse fraction, while S still dominated in PM1. Median SO42– concentrations in PM1-2.5 and the coarse fraction were significantly lower than in winter. The enrichment factors and wind speed-direction analysis helped to reveal potential air pollution sources.
To conclude, according to the performed analyses, PM1-2.5 was influenced by the sources of the coarse fraction during all campaigns. The additional significant influence of sources producing the fine fraction was evident under increased relative humidity conditions.