Spatial heterogeneity and sources of atmospheric carbonyls during ozone episodes in the Pearl River Delta

Carbonyls play critical roles in tropospheric photochemistry, significantly influencing radical budgets and ozone (O 3 ) formation. Despite frequent O 3 pollution episodes in the Pearl River Delta (PRD), the spatial heterogeneity and sources of carbonyls, particularly long-chain aliphatic saturated aldehydes (≥ C6), remain poorly characterized. This study conducted large-scale grid-based sampling analysis of 23 carbonyls across 35 sites in the PRD during spring and autumn O 3 pollution episodes in 2021. Higher concentrations were observed in the eastern PRD and Pearl River Estuary compared to the western PRD, with formaldehyde, acetaldehyde, acetone, and 2-butanone dominating the carbonyl profile. Short-chain carbonyls (C1 ∼ C5) exhibited strong correlations with industrial density, confirming anthropogenic dominance. Long-chain aldehydes showed non-biogenic characteristics, with significant contributions from cooking, shipping, and industrial processes involving fatty acids. Ozone formation potential analysis revealed that formaldehyde and acetaldehyde remained the principal contributors to O 3 formation. However, the contribution of long-chain aldehydes was substantial at specific local sites (notably some rural locations), in some cases exceeding that of short-chain aldehydes. Our findings underscore the need for targeted control strategies addressing both short-chain and long-chain carbonyls, particularly from industrial and cooking-related sources. • Grid-based sampling mapped spatial heterogeneity of carbonyls across the PRD. • Anthropogenic activities dominated carbonyl pollution dynamics, driving spatial heterogeneity. • Non-biogenic sources dominate long-chain aliphatic saturated aldehyde emissions in suburban and urban area in the PRD. • Long-chain aldehydes demonstrated non-negligible O 3 formation potential at localized pollution hotspots.