Linking air stagnation in Europe with the large-scale atmosphericcirculation

Abstract. The build-up of pollutants to harmful levels can occur when meteorological conditions favour their production or accumulation near the surface. Previous studies have shown that such conditions are often associated with air stagnation. Understanding the development of stagnant conditions is therefore crucial for studying poor air quality. The link between European air stagnation and the large-scale circulation is investigated in this article across all seasons and the 1979–2018 period. Dynamical based indices identifying atmospheric blocking, Rossby wave breaking, subtropical ridges, and the North Atlantic eddy-driven and subtropical jets are used to describe the large-scale circulation as predictors in a statistical model of air stagnation variability. It is found that the large-scale circulation can explain approximately 60 % of the variance in monthly air stagnation in five distinct regions within Europe. The variance explained by the model does not vary strongly across regions and seasons. However, the dynamical indices most related to air stagnation do depend on region and season. The blocking and Rossby wave breaking predictors tend to be the most important for describing air stagnation variability in northern regions whereas ridges and the subtropical jet are more important to the south. The demonstrated correspondence between air stagnation and the large-scale circulation can be used to assess the representation of stagnation in climate models, which is key for understanding how air quality and its associated health risks may change in the future.