Temporal variations and source analysis of ambient carbonyls in Hangzhou: A city-level study in the Yangtze River Delta region, China

Carbonyls play an important role in the atmospheric chemistry as the main precursor for reactive radicals and peroxyacetyl nitrate. However, little research has been conducted so far on the seasonal variations of carbonyls in China's urban atmosphere. In this study, ambient carbonyls were 24-hourly observed in four seasons in Hangzhou, a mega-city in the Yangtze River Delta Region, China. The concentration of total carbonyls was the highest in summer (44.35 µg/m³), the second in winter (44.05 µg/m³), the third in spring (29.31 µg/m³) and autumn (27.11 µg/m³). The most abundant species were found to be acetone in spring, summer, and winter, while formaldehyde in autumn. Rainfall can significantly reduce the concentrations of most ambient carbonyls, with the largest decrease observed in the wet precipitation events occurring in spring and summer, while acetone concentrations remained invariable due to its lower water solubility. Multiple linear regression analysis and carbonyls ratios indicated that anthropogenic emissions were the predominant sources of carbonyls, and atmospheric formaldehyde was mainly emitted from primary sources other than secondary sources. Vehicular exhaust was identified as the primary source of ambient carbonyls, particularly in winter, and its contribution reached 92.80 % to formaldehyde. Additionally, photochemical reactions were closely associated with the secondary production of formaldehyde in summer. Carbonyls showed strong ozone formation potential in all four seasons. Based on the health risk assessment, the exposure to ambient carbonyls is harmful to outdoor pedestrians. The results could provide essential information and references for simulating regional air quality and analyzing ozone pollution, which is essential for improving air quality in the Yangtze River Delta region.