Long-term (2012–2020) PM10 concentrations and increasing trends in the Sistan Basin: The role of Levar wind and synoptic meteorology

Abstract

The Sistan Basin in southeast Iran is one of the windiest and dustiest arid environments over the globe. The present study analyses, for the first time, long-term (April 2012 to March 2020) PM10 concentrations taken in Zabol (31.0324° N, 61.4902° E), the main city in Sistan, aiming to investigate the pollution trends, to assess the seasonality and the contribution of dust, to study the effect of wind and other meteorological parameters and to associate the extreme dust-related PM10 episodes with synoptic meteorological conditions. The annual-mean PM10 concentration was 429 μg m−3, which is one of the highest over the globe, while in summer, PM10 increased up to 693 μg m−3, with most turbid months July and August. The mean PM10 concentrations were much higher than the median ones, driven by severe dust storms throughout the year (193 days with PM10 > 1000 μg m−3), but with higher frequency and intensity in summer. A statistically-significant increasing trend was found in PM10 concentrations from 2012 to 2020, associated with a pronounced increase in wind speed, especially after 2017. PM10 concentrations were significantly correlated with mean and maximum wind speeds (r = 0.46, 0.41), while the visibility was highly reduced by increasing wind speed and PM10 levels. Dust contributes most (∼64%) to AOD and consequently to PM10, while the highest (>90th percentile) PM10 concentrations, both in summer and winter, were linked to intensification of the Caspian Sea high-pressure system that modulates the wind regime and meteorological patterns in central and southwest Asia.