Spatiotemporal PM2.5-bound Polycyclic Aromatic Hydrocarbons Dynamics and Stochastic Cancer Risks in the Metropolitan Hubs of Central Asia  

Central Asian urban centers face persistent air quality challenges characterized by elevated fine particulate matter (PM2.5) concentrations stemming from rapid urbanization, intensive industrial activity, and a heavy reliance on coal-fired central heating plants. Despite the known hazardous nature of polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic and mutagenic, a critical paucity of longitudinal observational data exists for this region [1-3]. This study presents the first systematic, year-long assessment of 14 PM2.5-bound PAHs in Almaty and Astana, Kazakhstan, to characterize their environmental behavior and public health implications.Results indicated that the annual average concentrations of total PAHs were 144.9±109.1 ng/m³ in Almaty and 25.6±19.9 ng/m³ in Astana, with the most severe pollution recorded during the heating season. Notably, annual benzo[a]pyrene (BaP) concentrations exceeded international guideline values by 5 to 20 times. Almaty’s higher pollution burden is attributed to its coal-intensive heating and mountainous basin topography, which facilitates frequent temperature inversions and atmospheric stagnation, thereby trapping pollutants. Conversely, Astana’s open steppe landscape promotes better ventilation, though it remains susceptible to episodic accumulation during Siberian high-pressure events.A significant seasonal compositional shift was observed: while naphthalene was the dominant compound year-round, both cities exhibited a substantial increase in high-molecular-weight (4–6 rings) species during winter, driven by increased residential heating combustion. Source identification using diagnostic ratios and principal component analysis confirmed that coal and biomass combustion are the primary contributors to PM2.5-bound PAH levels during the heating season. In the non-heating season, the relative influence of traffic-related emissions and liquid-fuel combustion increased, especially in Astana.A stochastic human health risk assessment implemented via a Monte Carlo framework revealed alarming inhalation cancer risks. Under the WHO-recommended risk metrics, the probability of exceeding the 10-4 inhalation cancer risk threshold was 100% in Almaty and 77.8% in Astana. BaP and dibenz[a,h]anthracene were identified as the most consequential contributors to this risk. These findings emphasize the urgent need for annual regulatory standards and a transition toward cleaner energy sources to mitigate the severe health risks associated with wintertime air pollution in Central Asia. AcknowledgmentsThis research was funded by the Science Committee of the Ministry of Higher Education and Science of the Republic of Kazakhstan (Grant No. AP27510649, 2025-2027).References[1] Tursumbayeva et al. Cities of Central Asia: New hotspots of air pollution in the world. Atmospheric Environment. 309  (2023) 119901.[2] A. Omarova et al. Emerging threats in Сentral Asia: Comparative characterization of organic and elemental carbon in ambient PM2.5 in urban cities of Kazakhstan, Chemosphere. 370 (2025) 143968.[3] Mukhtarov et al. An episode-based assessment for the adverse effects of air mass trajectories on PM2.5 levels in Astana and Almaty, Kazakhstan, Urban Clim. 49 (2023) 101541.