Seasonal heterogeneity of ambient size-resolved aerosol particles inducing reactive oxygen species in coastal megacities

Abstract

This study aims to reveal the seasonal variations in reactive oxygen species (ROS) for the size-resolved ambient particulate matter (PM) collected over one year in a coastal megacity in southeastern China. Through electron paramagnetic resonance (EPR), hydroxyl radicals (·OH) and organic radicals (·R) were measured, with ·OH identified as the dominant species. ROS concentrations exhibited evident seasonality in the following order: winter (6.58 × 10¹¹ spins/m³) > fall (4.17 × 10¹¹ spins/m³) > summer (3.38 × 10¹¹ spins/m³) > spring (2.02 × 10¹¹ spins/m³). Fine-mode particles (PM_0–3.3) constitute less than 40% of PM mass but account for over 60% of the total ROS burden. A variety of water-soluble components such as Fe, Mn, Zn, NO₃⁻, and WSOC exhibited strong correlations with ROS (r > 0.6), of which FTIR confirmed the high aromaticity of WSOC, indicating the seasonal changes in photochemical aging. As revealed by positive matrix factorization (PMF) analysis, vehicle emissions (41.41%) and secondary aerosols (32.73%) contributed mainly to ROS formation, particularly for ·OH. Differently, combustion sources were a major contributor to ·R generation, especially in winter. Its toxicological significance is highlighted by the enrichment of redox-active and aromatic compounds in PM_0–3.3. These findings underscore the pressing need to develop seasonally adaptive control strategies targeting traffic-related and secondary emissions, with particular attention paid to ultrafine particle pollution in coastal urban environments.

Graphical abstract

Keywords

Aerosol particles / Seasonal heterogeneity / Reactive oxygen species / Source apportionment

Highlight

	● Control strategies for ROS in coastal aerosols should focus on the winter.
	● WSOC, Mn, Fe, and Zn exhibit strong positive correlations with ROS.
	● The control of emissions from aromatic pollutants should be prioritized.
	● Traffic and secondary sources dominated ROS formation.

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