Pollution sources affecting the oxidative potential of fine aerosols in a Portuguese urban-industrial area - an exploratory study

This study targets to determine the oxidative potential (OP) of fine aerosols in an urban-industrial area of the Lisbon Metropolitan Area (Portugal) and, in addition, to identify which pollution sources may have an impact on the OP levels of fine aerosols. For this purpose, thirty samples were selected from a set of 128 samples collected over one year (Dec 2019-Nov 2020), based on the highest load for each source (both mass and %) previously assessed by source apportionment studies (using Positive Matrix Factorisation, a total of 7 different sources were identified: soil, secondary sulphate, fuel-oil combustion, sea, vehicle non-exhaust, vehicle exhaust and industry). The OP associated with the water-soluble components of PM_2.5 was assessed using the dithiothreitol (DTT) method. The samples had a mean DTT activity (normalised to the mass) of 12.9 ± 6.6 pmol min^− 1 µg^− 1, ranging from 3.5 to 31.8 pmol min^− 1 µg^− 1. The DTT activity (normalised to the volume, \({\text{O}\text{P}}_{\text{V}}^{\text{D}\text{T}\text{T}}\) ) showed to have a significant positive association with PM_2.5 levels (R² = 0.714). Considering that the mass contributions of the different sources to the PM_2.5 levels were known, Spearman correlations were assessed and significant correlations were found between \({\text{O}\text{P}}_{\text{V}}^{\text{D}\text{T}\text{T}}\) and three different sources: vehicle exhaust (ρ = 0.647, p-value = 0.001), fuel-oil combustion (ρ = 0.523, p-value = 0.012) and industry (ρ = 0.463, p-value = 0.018). Using a multiple linear regression analysis, these three sources were found to explain 82% of the variability in \({\text{O}\text{P}}_{\text{V}}^{\text{D}\text{T}\text{T}}\) , with vehicle exhaust being the most influential source.