Characterization of Atmospheric Carbonyl Compounds and Their Environmental Impacts in Coastal Hong Kong

Abstract

Carbonyl compounds are critical air pollutants that contribute to photochemical air pollution and pose adverse health effects. Extensive research has focused on their role in continental atmosphere, but their presence and impact on the coastal marine atmosphere has been less explored, despite its crucial role in the global atmospheric circulation. Moreover, limited by the ability of available methods, studies mainly focused on formaldehyde, acetaldehyde and acetone, hindering a comprehensive understanding of photochemical pollution mechanism. To address this gap, this study investigated the abundance, distribution, sources, photochemical atmospheric transformations and health risks of 47 carbonyl compounds with carbon (C) numbers from 1 to 13 in the coastal marine atmosphere of subtropical China by employing the newly developed method based on ultra-high-performance liquid chromatography and electrospray ionization tandem mass spectrometry.

The observation revealed a clear structure-concentration relationship and spatiotemporal distribution in the coastal marine atmosphere, with significant abundances of aliphatic saturated aldehydes (C≥5) and di-carbonyls and higher concentration in late summer/autumn. Higher levels of most species were observed in open waters than in the fairways and sea channels, due to prominent photochemical formation from regional outflows in the Pearl River Estuary. In contrast, α, β-unsaturated aliphatic aldehydes and acetone were elevated in harbor areas.

Source analysis indicated the dominant contribution of secondary formation, especially for long-chain aldehydes (C≥6). Key findings emphasized the importance of carbonyl behaviors in their production. Species, like formaldehyde, acetaldehyde, and MEK significantly promoted the formation of other carbonyls, whereas aromatic carbonyls, α, β-unsaturated carbonyls and limona ketone tended to hinder these processes. Ship emissions were found to crucially contribute to the α, β-unsaturated aliphatic aldehydes and acetone, while ocean emissions made a notable contribution to long-chain aldehydes (C≥6), acetone and di-aldehydes in the coastal marine atmosphere. Additionally, continental flow from Pearl River Delta regions also played a major role.

Atmospheric transformations of carbonyl compounds play a crucial role in atmospheric chemical circulation and air quality modulation. They were recognized as vital contributors to atmospheric peroxyl radicals and atmospheric oxidation capacity. These processes lead to O3 and secondary organic aerosol (SOA) formation, with ozone formation potential primarily driven by formaldehyde and acetaldehyde, and additional contributions from long-chain carbonyls and di-carbonyls. Furthermore, the glyoxal, methylglyoxal, benzaldehyde and α, β-unsaturated aldehydes exhibited considerable contribution to SOA formation potential, highlighting the importance of various reactive carbonyls in the atmospheric chemistry of coastal regions.

Health risk assessment demonstrated that carbonyl compounds pose substantial carcinogenic and non-carcinogenic risks to maritime workers and other exposed populations, even exceeding risks faced by road workers, underscoring the necessity of considering carbonyl compounds in occupational exposure risk assessments.

In conclusion, this study provides a comprehensive overview of carbonyl compounds in the coastal marine atmosphere, shedding light on their multifaceted role in atmospheric chemistry and public health. The findings underscore the necessity of incorporating a wide range of carbonyl species into environmental monitoring and regulatory frameworks.

Date of Award	2025
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Zhe WANG (Supervisor) & Jianzhen YU (Supervisor)