Analysis of the impacts of atmospheric circulation patterns on the regional air quality over the geographical center of the Eurasian continent

摘要

There is growing scientific interest in the impact of atmospheric circulation on regional air quality; however, it is poorly studied in Central Asia. This study is the first assessment of the evidence-based relations between air pollution episodes and the elementary circulation mechanisms (ECMs, by the classification from Dzerdzeevskii a al.) with atmospheric blocking process effects on an urban atmosphere over the geographical center of the Eurasian continent. The capital city of Kazakhstan, Nur-Sultan, is selected as the study location since it is located in the north of the Kazakh Uplands in a dry steppe zone. First, an episode identification procedure using multiple stations and multiple-pollutant time series data is proposed. After the identification of the aggregated pollutant episodes during the heating and non-heating periods in 2017, their relations with blocking anticyclones and cyclones are further investigated by checking the reversal of meridional gradients in the 500 hPa and 850 hPa geopotential height (GPH) maps. In total, 12 and 9 pollution episodes lasting an average of 5 days were identified in heating and non-heating periods, respectively. Following the calendar of continuous ECM changes, the type of ECM is determined for each episode, and then, the types of ECMs with atmospheric circulation and trajectory characteristics corresponding to the episodes were analyzed in detail. The findings suggest that i) regional and local air pollution levels on the Eurasian Steppes are actively controlled by regional meteorological variations, ii) the northern streams of cold Arctic air spread to the region and Siberian anticyclone reaches in winter, leading to extreme negative air temperature anomalies that contribute to the further cooling of the Arctic air and formation of extensive stationary anticyclones with blocking effects over the region, iii) a cold season circulation type, ECM 13w, was one of the most dominant ECMs with approximately 23% annual prevalence causing 30% of all the episodes, iv) ECMs 11a, 5a, and 5b were also associated with much higher pollution levels (up to 4-fold increases over the annual average), but they had lower prevalences (up to 5%). As a result, it was demonstrated that the regional climate conditions with particular ECMs regulate the ventilation characteristics of the atmosphere over the study area, and local air pollution concentrations increase to extreme levels and remain there longer, particularly during stationary anticyclone periods.