Severe health risks from ambient volatile organic compounds (VOCs) in a Central Asian city: Source attribution and probabilistic risk assessment

Volatile organic compounds (VOCs) significantly contribute to ambient air pollution and pose serious health threats, particularly in rapidly urbanizing regions. This study comprehensively assessed ambient VOC concentrations, identified potential emission sources, and conducted a stochastic human health risk assessment in Almaty, Kazakhstan – a metropolitan Central Asian city characterized by intense traffic, extensive coal combustion, and frequent temperature inversions. Ambient air samples were collected seasonally at multiple elevation points across the city and analyzed for 23 VOC species. Their concentrations were notably elevated during the heating season, especially in the lower city, with benzene, toluene, ethylbenzene, xylenes (BTEX), and naphthalene exhibiting alarming levels compared to other urban settings worldwide. Principal component and BTEX ratio analyses identified coal combustion, vehicle emissions, and industrial activities as the primary VOC sources, with persistent impacts observed even during non-heating seasons due to pollutant resuspension and revolatilization. The stochastic health risk assessment revealed median non-carcinogenic hazard indices generally within acceptable limits but highlighted substantial exceedances (HI > 1) at the 95th percentile, driven mainly by benzene and naphthalene. Carcinogenic risks consistently exceeded acceptable thresholds (10⁻⁶), with benzene being the predominant contributor, which raised urgent public health concerns. Almaty's population faces significantly higher cancer risks than North American and European cities, highlighting the critical need for targeted regulatory measures to mitigate VOC emissions and protect public health.