The 5-year trend of PM1 and PM2.5 mass concentrations and their carbon content at an urban background site in Zagreb, Croatia

Fine particulate matter, such as PM2.5 and PM1, is a harmful air pollutant from natural and human sources. It impacts the climate and causes respiratory issues. It's classified as a Group 1 carcinogen, and it's the most harmful form of air pollution, causing heart and lung disease and premature death. Aerosols' composition and toxicity vary depending on their source and atmospheric chemistry. The carbon fraction of particulate matter, consisting of both elemental and organic carbon, may cause adverse health effects due to its reductive potential and organic species. It also contributes to global warming due to its radiative properties. Carbonaceous material is a substantial part of particulate matter, with primary organic carbon coming from incomplete combustion and degradation of carbon-containing products. Secondary organic carbon forms through the condensation of organic carbon gases from organic material combustion, fuel evaporation, or natural volatile organic compounds emission.The objective of this study was to identify and compare the concentrations of elemental carbon (EC) and organic carbon (OC) in PM2.5 and PM1 particles during different seasons and years in order to detect any potential trends of individual pollutants in PM at a single site in Zagreb. Continuous monitoring of mass concentrations of PM1 and PM2.5 particles, along with their carbon content, was carried out for a period of five years, starting from January 1st, 2018, and ending on December 31st, 2022, at an urban background site located in the northern part of Zagreb. Daily samples of PM1 and PM2.5 particle fractions were gathered on pre-fired quartz fiber. Their mass concentrations were determined gravimetrically, while carbon content was analyzed for OC, TC, WSOC, and EC. This was done using the thermal-optical transmittance method, following the EUSAAR_2 protocol. The measurements taken over 5 years showed that the concentration of carbon species in PM1 and PM2.5 varied seasonally. The concentration of carbon pollutants was observed to be higher during cold periods, while it was lower during warmer periods of the 5-year campaign. A weak downward trend in PM1, PM2.5, and OC mass concentrations was observed during the studied period, while EC mass concentrations showed a slight increasing trend. ACKNOWLEDGEMENTS: These measurements were conducted within the internal scientific project of the Institute for Medical Research and Occupational Health “Organic content of PM1 particle fraction” (PI: R. Godec). The results of this research were obtained using the facilities and equipment funded within the European Regional Development Fund project KK.01.1.1.02.0007 "Research and Education Centre of Environmental Health and Radiation Protection – Reconstruction and Expansion of the Institute for Medical Research and Occupational Health".