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arXiv · 2510.03030

Global impacts of organic aerosol acidity on sulfate and cloud formation

Gargi Sengupta·Kunal Ghosh·Prithvi R. Jallu·Nønne L. Prisle
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Abstract

Organic aerosols (OA) comprise a major fraction of atmospheric particulate matter and frequently contain acidic species, yet their contribution to overall aerosol acidity has not been explicitly considered in global climate models. We implement concentration-dependent OA acid dissociation, including recently demonstrated surface-specific effects, into the ECHAM-HAMMOZ global climate model and assess the impacts on aqueous aerosol sulfate chemistry and aerosol--cloud--climate interactions. We show that enhanced aerosol acidity from OA acid dissociation drives increased sulfate formation from aqueous-phase oxidation of $\mathrm{SO_2}$. The microphysics of additional secondary sulfate aerosol changes global cloud droplet number concentrations (CDNC), with enhancements up to $13.9\%$. Increased cloud formation leads to a significant global mean cooling effect with a shortwave cloud radiative forcing (SWCRF) up to $-0.97~\mathrm{W\,m^{-2}}$. We also find that surface-specific acid dissociation effects can further modify both aerosol chemistry and resulting aerosol--cloud--climate responses, in some cases with even stronger impact than bulk acidity conditions. Our results demonstrate significant effects of considering OA acidity, as well as surface-specific phenomena, in global climate models.

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Gargi Sengupta, Kunal Ghosh, Prithvi R. Jallu, Nønne L. Prisle. 2025-10-03. Global impacts of organic aerosol acidity on sulfate and cloud formation. https://arxiv.org/abs/2510.03030

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