Emitted yesterday, polluting today: temporal source apportionment of fine particulate matter pollution over Central Europe

Abstract. Fine particulate matter (PM2.5) pollution remains a critical health issue in Europe. While numerous studies have quantified the spatio-sectoral sources of urban PM, the temporal origin has received minimum attention. This study addresses this gap by developing a novel Temporal Source Apportionment approach within the CAMx chemical transport model to quantify the long-term contributions of emissions from the preceding 14 days to PM concentrations, focusing on the 2010–2019 period and Central Europe. The results show that current-day emissions dominate winter PM2.5, contributing 30–60% on average, while day-1 emissions add further 20–30%. Contributions decrease with emission age, falling below 5% after three days and becoming negligible beyond seven days. Secondary inorganic aerosols and primary organic aerosols exhibit similar patterns, although for winter nitrate levels, the highest contribution comes from day-1 emissions, reflecting the time needed for chemical formation. Summer contributions are smaller due to enhanced mixing and faster removal, whereas biogenic emissions also contribute largely giving anthropogenic emissions a smaller role. Importantly, while the average contribution of older emissions is low, occasional episodes show substantial impacts: day-4 emissions can contribute up to 10%, and even week-old emissions can add 2% in winter. These findings emphasize that adverse air quality episodes are influenced not only by same-day emissions but also by pollution accumulated from previous days resulting from past emissions. Effective mitigation policies on PM pollution must therefore consider reducing emissions several days in advance of predicted pollution episodes, rather than relying solely on same-day interventions.