Ionic composition of PM2.5 particle fraction at a coastal urban background site in Croatia

The mass concentrations and content of water-soluble anions (Cl−, NO3−, SO42−) and cations (Na+, NH4+, K+, Mg2+, Ca2+) in the PM2.5 particle fraction were measured, and an investigation of their relationship and their contribution to the total PM2.5 mass measured was conducted at an urban background site as part of the Croatian monitoring network for air quality located in Rijeka, Croatia. Daily samples of PM2.5 particle fraction were collected over 2017 on PTFE filters using a low volume sampler Sven Leckel SEQ 47/50. Mass concentrations of the PM2.5 particle fraction were determined by gravimetry according to the standard HRN EN 12341:2014 (EN 12341:2014). The content of water-soluble inorganic anions and cations were determined using a Thermo Scientific ICS-5000 capillary ion chromatograph. Results show that the annual average PM2.5 mass concentration was 9.65 μg m-3 and did not exceed the limit value of 25 μg m-3 given by the Regulation on the level of pollutants in air (OG No. 117/12). The annual average mass concentrations of ions in PM2.5 particle fraction was SO42−> NH4+> NO3− > Ca2+> K+> Na+> Cl− > Mg2+. The contributions of total anion mass and total cation mass to the total PM2.5 mass were 25.4% and 12.8%, respectively. The acidic property of PM2.5 was obtained in spring and winter and slightly acidic in summer and autumn. For a prediction of the pollutant sources, we ran a factor analysis which was performed using the statistical packages STATISTICA 13.0. After varimax rotation, the obtained four principal component factors were found to account for 86% of the variance. Factor loadings > 0.7 were considered significant. •The annual average mass concentrations of PM2.5 did not exceed the limit value.•The average ion mass concentrations was SO42− > NH4+> NO3− > Ca2+> K+> Na+> Cl− > Mg2+.•The most contributing ions to the total PM2.5 mass were SO42−, NH4+ and NO3−•Strong correlation indicated presence secondary aerosols (NH4)2SO4, NH4HSO4, NH4NO3.•Results implies acidic property of PM2.5