Urban atmospheric volatile organic compounds pollution in Kazakhstan: Trends, Sources identification, and Health risk assessment

Abstract
Volatile organic compounds (VOCs) are significant atmospheric pollutants that cause adverse effects on climate and public health, impact demographics, and economic losses. VOCs contribute to the formation of ground-level ozone and secondary organic aerosols (SOA), exacerbating smog and global warming. While VOCs are recognized globally as precursors, regions like Kazakhstan lack sufficient monitoring and assessments for effective air quality. This first comprehensive, year-long study (2022–2023) conducted in two urban cities in Kazakhstan assesses seasonal variations, characterizes sources using HYSPLIT and diagnostic ratios, and quantifies health risks. Annual 18 VOC concentrations were 0.07–12.03 μg/m3 in Almaty and 0.10–5.52 μg/m3 in Astana. HYSPLIT results demonstrated Almaty's seasonal VOC variations reflect local and transboundary sources, peaking in winter due to stagnant conditions, while Astana's air masses consistently revealed influences from petrochemical, combustion, and industrial activities. Almaty exhibited a higher cumulative non-carcinogenic risk (HI = 0.66) than Astana (0.27), with benzene, xylenes, and naphthalene as main contributors. HI exceeded the risk threshold (21 out of 97 sampling days) in winter and spring in Almaty, while Astana's risks remain negligible. Mean cumulative lifetime cancer risk (LTCR) in Almaty (3.14 × 10−4) indicated a higher cancer risk (314 cases/million) than Astana (103 cases/million), with benzene as the primary contributor to LTCR (Almaty: 67.6%, Astana: 87.0%). VOCs' reactivity linked xylenes, toluene, and pseudocumene contributed >80% to ozone formation potential, and BTEX >96% to SOA formation potential in both cities. The study recommends prioritizing regulations on reactive VOCs (BTEX, pseudocumene), with stricter benzene limits to meet WHO standards and reduce health risks.