Surface Nitrate Enrichment and Enhanced HONO Production from Ionic Surfactant Aggregation at the Aqueous-Air Interface

Significant discrepancies persist between field observations and model simulations regarding the strength of marine-derived HONO sources, underscoring the urgency to resolve unidentified HONO sources. In this study, sodium dodecyl sulfate (SDS) was chosen as a proxy for marine surfactants to investigate its impact on aqueous nitrate photolysis for the first time. Remarkable increases in HONO and NO2 production rates by factors of 3.3 and 5.6, respectively, along with a 1.9-fold rise in NO2 - concentration, were observed at a very low SDS concentration of 0.01 mM, strongly illustrating the promoting effect on nitrate photolysis. Furthermore, at an SDS concentration of 2 mM, intriguingly aligned with the critical micelle concentration, there was an additional 41.7% increase in HONO production rates. Vertically resolved Raman measurements indicated that SDS anions at the aqueous-air interface attracted NO3 - closer to the aqueous surfaces, increasing the amount of incompletely solvated surface nitrate. Importantly, the anionic surfactant exhibited a greater promoting effect on HONO production compared to other typical nitrate photochemistry systems with the addition of a marine dissolved organic matter proxy, halogen, photosensitizer, or OH scavenger. These findings offer new insights into marine-derived HONO sources and should be considered in model simulations concerning the budgets of NO x , OH, and O3.