Krzysztof M. Markowicz

We present the first estimations of single hygroscopic parameter κ for Polish urban area. The results were obtained using an inexpensive OPC-N3 optical particulate matter counter and the ASC 1000 Acoem Aerosol Conditioning System. Our studies were carried out during the winter and spring seasons, between 2020 and 2022 in Warsaw, Poland. We study the difference of κ between these two seasons, as the aerosol has different origins. The mean value of the hygroscopicity parameter for spring (April–June) was 0.13±0.13 and for winter (December-March) it was 0.04±0.04 (obtained using PM1). The mean value of the growth factor for spring (April–June) was 1.52±0.23 and for winter (December–March) it was 1.16±0.13 (obtained using PM1). The values for winter period suggest that during the cold season the aerosol mixture in the atmosphere is dominated by non-hygroscopic particles. However events of higher κ > 0.5 where occurring (mostly for big aerosol particles 1–10 μm in size), when the air mass was coming from North Atlantic carrying sea salt particles. Furthermore, based on κ we propose a method to remove the dependence of PM values on relative humidity on the OPC-N3 optical particulate counter.