Nitrogen dioxide and sea salt particles—A laboratory study

The reaction between NO2 at sub-ppm levels and wet or dry sea salt particles was studied using a thermostatted flow reactor. The results indicate that the major pathway for nitrogen dioxide reaction, both for dry particles and droplets, is 2NO2 (g,aq)+Cl−(s,aq)→NO3−(s,aq)+NOCl (g). The reaction between dry sea salt aerosol and NO2 is rapid but ceases when less than a monolayer of NaNO3 has been formed. The reaction between near-saturated sea salt droplets and NO2 appears to proceed via a liquid-phase process analogous to the reaction between dry sea salt and NO2. The liquid reaction has a potential to form 0.003 μg NO3− m−3 h−1 at conditions typical for the polluted marine atmosphere. If NOCl, produced in the sea salt droplets, survives hydrolysis it may give a significant contribution to atomic chlorine via photolysis.