Dominant sources of PM2. 5 in Kazakhstan's urban cities: A PMF and HYSPLIT-based study for air quality management in Central Asia

Abstract
Effective air quality management in Central Asian cities is hindered by limited knowledge of PM2.5 sources. This study employed Positive Matrix Factorization (PMF) for source apportionment of PM2.5 in two urban cities in Kazakhstan (Almaty and Astana), representing the first comprehensive analysis for Almaty. An extensive year-long sampling campaign (August 2022–July 2023) collected PM2.5 samples for detailed chemical characterization, including organic/elemental carbon, elements, anions, and cations. PMF results revealed five distinct sources, contributing between 14 % and 32 % to ambient PM2.5 in both cities. Although pollution sources showed a relatively uniform distribution, several factors strongly correlated with coal and biomass combustion, which emerged as the predominant contributors to PM2.5, highlighting their key role in urban air quality in both cities. Regional and local source influences were identified using HYSPLIT backward trajectory and Conditional Probability Function (CPF) analysis. In Almaty, dominant trajectory clusters at different altitudes involved slow-moving air masses, indicating a significant impact from urban road dust resuspension. In Astana, backward trajectory analysis demonstrated that a substantial proportion of air masses traverse nearby industrial regions (Karagandy and Pavlodar), elevating PM2.5 levels. The findings highlighted the considerable contribution of coal combustion to PM2.5 pollution and emphasized the need for stringent emission controls and evidence-based strategies to improve air quality and safeguard public health in Central Asian cities. The study proposes achievable interim PM2.5 reduction targets for Astana and Almaty, reflecting considerable reductions from current levels.