The impact of seasonality and meteorological conditions on PM2.5 carbonaceous fractions coupled with carbon isotope analysis: Advantages, weaknesses and interpretation pitfalls

Abstract

PM2.5 samples were collected from October 2020 to September 2021 in Legnica in the Lower Silesia Voivodeship (SW Poland), where environmental guidelines are often exceeded. In order to have a better insight into the respective inputs of local and regional sources concentrations of PM2.5, carbonaceous fractions (TC/OC/EC), carbon isotope composition (δ13CTC) and FTIR spectra of PM2.5 were studied in parallel. The objectives of this study were to (i) identify the emission sources controlling the local aerosol budget and to (ii) discuss the potential limits of the approach used. We highlighted a seasonality in the concentrations of PM2.5, TC, OC, and EC, with higher concentrations in winter resulting of an increased activity of local emission sources coupled to the occurrence of specific meteorological conditions. While we identified coal burning as the main source of pollution in winter, a mix of emissions from coal and bio/organic combustion and road traffic explains the pollution levels in summer. Coupling these findings with the study of FTIR spectra, we corroborated that incomplete combustion of fossil fuels is a major source in winter whereas biogenic particles are in summer. Despite the observed seasonal variations in the OC and EC concentrations, the OC/EC ratios did not show significant variations. It suggests that this ratio, if used as a single proxy to infer sources of carbonaceous aerosols, may lead to interpretation pitfalls. Our results strongly suggest that a multi-proxy approach that couples TC/OC/EC and FTIR to carbon isotope geochemistry provides a reliable evaluation tool for air quality and brings strong constraints on the corresponding sources of PM2.5.