Nocturnal loss and daytime source of nitrous acid through reactive uptake and displacement

• Published in: Nature geoscience Vol. 8; no. 1; pp. 55 - 60
• Main Authors: VandenBoer, Trevor C., Young, Cora J., Talukdar, Ranajit K., Markovic, Milos Z., Brown, Steven S., Roberts, James M., Murphy, Jennifer G.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.01.2015; Nature Publishing Group
• Subjects: 704/106/35/824; 704/172/169/209; 704/172/169/824; Carbonates; Earth Sciences; Earth System Sciences; Emissions; Geochemistry; Geology; Geophysics/Geodesy; Nitric acid; Photochemicals; Soils; Urban agriculture
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/ngeo2298

The nature of daytime sources and night-time sinks of nitrous acid is a key uncertainty in understanding atmospheric oxidation and radical cycling. The accumulation of nitrous acid in the air has been observed to slow down during the night, implying the presence of a night-time sink. In addition, there may be a photochemical source of nitrous acid during the daytime. We used flow tube experiments, measurements of acid displacement efficiencies, and field monitoring of nitrous acid and nitrite concentrations to study the exchange of nitrous acid with soils. Here we show that nitrous acid can react with carbonates or soil at night and subsequently be displaced from soils during the day by air-to-soil transfer of hydrogen chloride and nitric acid, which are generated in the atmosphere photochemically. These processes provide a critical link between the sink of nitrous acid at night and its emission the following day. We conclude that the acid displacement process could contribute a substantial fraction of daytime nitrous acid emissions in numerous environments, including agricultural, urban and vegetated regions, and in any location subject to deposition of soil-derived mineral dust. Nitrous acid cycling contributes significantly to the atmospheric oxidation capacity. Flow tube experiments and field monitoring reveal a night-time nitrous acid sink in soils, and subsequent release during the day.