Extensive field evidence for the release of HONO from the photolysis of nitrate aerosols

Particulate nitrate (pNO(3)(-)) has long been considered a permanent sink for NOx (NO and NO2), removing a gaseous pollutant that is central to air quality and that influences the global self-cleansing capacity of the atmosphere. Evidence is emerging that photolysis of pNO(3)(-)can recycle HONO and NOx back to the gas phase with potentially important implications for tropospheric ozone and OH budgets; however, there are substantial discrepancies in renoxification photolysis rate constants. Using aircraft and ground-based HONO observations in the remote Atlantic troposphere, we show evidence for renoxification occurring on mixed marine aerosols with an efficiency that increases with relative humidity and decreases with the concentration of pNO(3)(-), thus largely reconciling the very large discrepancies in renoxification photolysis rate constants found across multiple laboratory and field studies. Active release of HONO from aerosol has important implications for atmospheric oxidants such as OH and O-3 in both polluted and clean environments.

Automated summary

Particulate nitrate (pNO(3)(-)) has traditionally been considered a sink for NOx, but recent evidence shows that it can be recycled back to the gas phase through photolysis, with implications for tropospheric ozone and OH budgets. This study provides evidence of renoxification occurring on marine aerosols in the remote Atlantic troposphere, reconciling discrepancies in renoxification rate constants found in previous studies. The active release of HONO from aerosols has important implications for atmospheric oxidants in both polluted and clean environments.