Linking air stagnation in Europe with the synoptic- to large-scale atmospheric circulation

Abstract

Abstract. The build-up of pollutants to harmful levels can occur when meteorological conditions favour their production or accumulation near the surface. Such conditions can arise when a region experiences air stagnation. The link between European air stagnation, air pollution and the synoptic- to large-scale circulation is investigated in this article across all seasons and the 1979–2018 period. Dynamical indices identifying atmospheric blocking, Rossby wave breaking, subtropical ridges, and the North Atlantic eddy-driven and subtropical jets are used to describe the synoptic- to large-scale circulation as predictors in statistical models of air stagnation and pollutant variability. It is found that the large-scale circulation can explain approximately 60 % of the variance in monthly air stagnation, ozone and wintertime particulate matter (PM) in five distinct regions within Europe. The variance explained by the model does not vary strongly across regions and seasons, apart from for PM when the skill is highest in winter. 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 and pollutant variability in northern regions, whereas ridges and the subtropical jet are more important to the south. The demonstrated correspondence between air stagnation, pollution and the large-scale circulation can be used to assess the representation of stagnation in climate models, which is key for understanding how air stagnation and its associated climatic impacts may change in the future.

A storyline view of the projected role of remote drivers on summer air stagnation in Europe and the United States

“…This index considers a day as stagnant when three conditions are simultaneously fulfilled within a grid cell: near-surface wind speed <3.2 m s −1 , 500 hPa wind speed <13.0 m s −1 , and accumulated precipitation <1.0 mm. Previous analyses have found that this formulation of the ASI outperforms others in capturing the links among large-scale circulation, stagnation, and air pollution in Europe (Garrido-Perez et al 2021, Maddison et al 2021). This index is also commonly used for air pollution studies in the U.S. (Schnell andPrather 2017, Sun et al 2017).…”

“…We define air stagnation using the National Climate Data Center Air Stagnation Index (ASI; Wang and Angell 1999) adaptation by Horton et al (2012), a commonly used metric in air quality meteorology studies (Leung and Gustafson 2005, Horton et al 2012, 2014, Huang et al 2017, Maddison et al 2021. This index considers a day as stagnant when three conditions are simultaneously fulfilled within a grid cell: near-surface wind speed <3.2 m s −1 , 500 hPa wind speed <13.0 m s −1 , and accumulated precipitation <1.0 mm.…”

Modulation of European air quality by Euro-Atlantic weather regimes

“…The resulting number of predictors ranges from two to seven and is around five on average over the whole domain for all pollutants. The stepwise algorithm employed in this study is the same as in Garrido-Perez et al (2021) and Maddison et al (2021) (see details in their methods sections). This algorithm ensures noncollinearity between the explanatory variables, which is an essential assumption of MLRMs.…”

“…While anthropogenic emissions are the main source of air pollutants, observational studies have illustrated that the variability of their concentrations is closely related to changes in weather conditions (Fiore et al, 2015). In particular, the dependence of air pollution on the largescale circulation has been subject of comprehensive analyses (Pausata et al, 2013;Chang et al, 2016;Webber et al, 2017;Xu et al, 2017;Ordóñez et al, 2019;Maddison et al, 2021). Recent reports have evidenced that air pollution over Europe is quite sensitive to the location of anticyclonic systems.…”

Added value of a multiparametric eddy-driven jet diagnostic for understanding European air stagnation

“…Understanding the drivers of air stagnation events can provide information that may be beneficial for seasonal forecasting and climate change projections, where directly identifying air stagnation or pollution extremes can be challenging. Surface weather conditions in Europe, including air stagnation, are strongly governed by the synopticto large-scale circulation over the region (Gaetani et al 2011, Mahlstein et al 2012, Santos et al 2013, Maddison et al 2021. Air stagnation has been linked to the North Atlantic-European atmospheric circulation (Maddison et al 2021) through circulation features associated with high pressure systems, such as blocks (Hamburger et al 2011, Garrido-Perez et al 2017, Vautard et al 2018, Rossby wave breaking (Webber et al 2017), and subtropical ridges (Ordó nez et al 2017, Maddison et al 2021).…”