A marked interannual variability of haze linked to particulate sources and meteorological conditions in Tehran (Iran), 1990–2020

Abstract

This research assessed the spatio-temporal changes of haze pollution (NHAZEs) and its relationship with levels of gaseous pollutants and meteorological conditions over Tehran metropolis (Iran) for 1990–2020. The results showed a significant decreasing trend of NHAZEs annually and in winter, along with a significant increasing trend in the horizontal visibility. However, a marked interannual variability linked to changes in PM2.5 concentrations and the influence of meteorological conditions was detected, which explained 65% and 30% of the NHAZEs variances, respectively. We found that the increasing trend of wind speed annually and in winter is the principal driver behind the decrease in NHAZEs and the increase in visibility; as winds control the movement and dispersion of air pollution. In relation to gaseous pollutants, a case study showed that the highest concentrations of PM2.5 and NHAZEs were recorded under high levels of SO2, CO, and NO2, and low levels of O3, which mainly occurred under stable anticyclonic circulations. Spatially, the NHAZEs mostly affected the western, southwestern, central, and some parts of the northern of Tehran metropolis, because of the location of industries, traffic, and lack of green areas.