Exploring the most influential part of atmospheric circulation in the formation of severe air pollution episodes in the Greater Tehran

Availability of long-term data, information, and weather charts are essential parts of providing an accurate weather forecast by the synoptic method. The availability of air pollution data and information indicators from 1999 have imposed limitations in precise recognition of influential weather conditions on the formation of acute air pollution episodes, timely implementation of pollution control measures, and its management. One way of resolving those problems is to find out more similar synoptic circulation patterns in the past. To do that, two statistical methods, i.e., wavelet transform and bootstrap significance test, have been employed to identify more important and significant features of atmospheric circulation that provide suitable conditions for the formation of those episodes. The method has been used to extend the data and information availability to 30 years. Those methods not only helped us to find more synoptic circulation patterns associated with intense air pollution episodes but also made the process of finding them simple, fast, and precise. By this study, we have found that the transient weather systems that passes over the north of Europe and Russia, cutoff lows over the eastern Mediterranean Sea, deflection of high-speed atmospheric currents (jet streams) over the Scandinavian region towards the south, presence of a pressure ridge over the west of the region of study, appearance of a low center above the north of the Caspian Sea, and low-pressure areas over the Arabian Sea and North Indian Ocean (especially during the Monsoon season) have been the most influential parts of atmospheric circulation in the formation of highly polluted episodes in Tehran.