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Chemical Compositions and Acidity of PM2.5 Aerosol in Zagreb Air, CROATIA

Fine particles (i.e. PM2.5) are well known to be associated with human health, air quality deterioration and global climate change. Aerosol acidity is an important property of particles. It is well known that Cl-, NO3 -, and SO4 2- are favorable for the acidity of aerosols, whereas Na+, NH4 +, K+, Mg2+, and Ca2+ increase the pH of air particles. Daily PM2.5 samples were taken over a year 2014 in northern part of Zagreb air with moderate to high traffic density. Samples were analysed for water-soluble anion species (Cl-, NO3 -, SO4 2-) and cation species (Na+, NH4 +, K+, Mg2+, Ca2+). Mass concentrations of PM2.5 particle fraction were determined by gravimetry according to the standard HRN EN 14907:2006 (EN 14907:2005). Water-soluble ionic species were analysed using Thermo Scientific – ICS 5000 Capillary ion chromatography. PM2.5 mass concentration was significantly influenced by the season, reaching their high values in the winter. Annual average PM2.5 mass concentration was 19.6 g m-3. The annual average ion mass concentrations followed the order SO4 2->NO3 ->NH4 +>K+>Ca2+>Cl->Na+> Mg2+. The ion balance were taken as an indicator to stady the acidity of aerosols, which was determined by both anion equivalents (AE) and cation equivalents (CE). The AC/CE ratio was calculated. The neutralisation factor (NF) is calculated to evaluate the neutralization capacity of measured cation species. The highest value was measured for NH4 + suggested that acidic anions in PM2.5 were mainly neutralized by NH4 +.

anion equivalents (AE); cation equivalents (CE); AC/CE ratio; neutralisation factor (NF); ion balance

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