Carbonyls play critical roles in tropospheric photochemistry, significantly influencing radical budgets and ozone (O3) formation. Despite frequent O3 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 O3 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 O3 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.
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