Acidity across the interface from the ocean surface to sea spray aerosol

Aerosols impact climate, human health, and the chemistry of the atmosphere, and aerosol pH plays a major role in the physicochemical properties of the aerosol. However, there remains uncertainty as to whether aerosols are acidic, neutral, or basic. In this research, we show that the pH of freshly emitted (nascent) sea spray aerosols is significantly lower than that of sea water (approximately four pH units, with pH being a log scale value) and that smaller aerosol particles below 1 mu m in diameter have pH values that are even lower. These measurements of nascent sea spray aerosol pH, performed in a unique ocean-atmosphere facility, provide convincing data to show that acidification occurs across the interface within minutes, when aerosols formed from ocean surface waters become airborne. We also show there is a correlation between aerosol acidity and dissolved carbon dioxide but no correlation with marine biology within the seawater. We discuss the mechanisms and contributing factors to this acidity and its implications on atmospheric chemistry.

Automated summary

This research demonstrates that freshly emitted sea spray aerosols have significantly lower pH values than seawater, with smaller aerosol particles having even lower pH values. Aerosol acidity is found to be correlated with dissolved carbon dioxide but not with marine biology within seawater. The study discusses the mechanisms and implications of this acidity on atmospheric chemistry.