Surface Nitrate\nEnrichment and Enhanced HONO Production\nfrom Ionic Surfactant Aggregation at the Aqueous-Air Interface

Significant discrepancies persist between field observations\nand\nmodel simulations regarding the strength of marine-derived HONO sources,\nunderscoring the urgency to resolve unidentified HONO sources. In\nthis study, sodium dodecyl sulfate (SDS) was chosen as a proxy for\nmarine surfactants to investigate its impact on aqueous nitrate photolysis\nfor the first time. Remarkable increases in HONO and NO<sub>2</sub> production rates by factors of 3.3 and 5.6, respectively, along\nwith a 1.9-fold rise in NO<sub>2</sub><sup>–</sup> concentration,\nwere observed at a very low SDS concentration of 0.01 mM, strongly\nillustrating the promoting effect on nitrate photolysis. Furthermore,\nat an SDS concentration of 2 mM, intriguingly aligned with the critical\nmicelle concentration, there was an additional 41.7% increase in HONO\nproduction rates. Vertically resolved Raman measurements indicated\nthat SDS anions at the aqueous-air interface attracted NO<sub>3</sub><sup>–</sup> closer to the aqueous surfaces, increasing the\namount of incompletely solvated surface nitrate. Importantly, the\nanionic surfactant exhibited a greater promoting effect on HONO production\ncompared to other typical nitrate photochemistry systems with the\naddition of a marine dissolved organic matter proxy, halogen, photosensitizer,\nor OH scavenger. These findings offer new insights into marine-derived\nHONO sources and should be considered in model simulations concerning\nthe budgets of NO<sub><i>x</i></sub>, OH, and O<sub>3</sub>.