Assessment of ambient particulate matter and trace gases in Istanbul: Insights from long-term and multi-monitoring stations

In this study, the long-term spatio-temporal variation, trends, and source increments of particulate matter (PM₁₀ and PM_2.5) and gaseous pollutants (SO₂, NO, NO₂, CO, O₃) measured from 2015 to 2021 across 37 air quality monitoring stations in the European and Asian sides of Istanbul were investigated. The average PM₁₀ concentration on the European side is higher than the Asian side. However, the average PM_2.5 in both regions showed the same values. The results show that the industries near urban sites mainly affect PM₁₀ concentrations in Istanbul. Ship emissions (from the Istanbul Strait) make the largest incremental contribution to SO₂ and CO (211% and 139%, respectively) among other pollutants. PM₁₀, PM_2.5, SO₂, and NO₂ concentrations show significant (p < 0.01) negative temporal trends of 6.02%, 6.97%, 5.38%, and 3.28%, respectively, most notable in the winter season. However, the CO and O₃ concentration trends are stable and increasing. According to the correlation coefficient (R) and the coefficient of divergence (COD) analysis, there is a heterogeneous distribution of pollutants at the intra-urban scale. PM_2.5 concentrations are dominated by diverse pollution sources such as traffic, shipping and regional sources.