Specific Ion Chemistry at the Air–Water Interface of Nitrite/Nitrate-Containing Droplets

High Resolution Image Download MS PowerPoint Slide An increasing number of studies report on the spontaneous production of OH radicals and H 2 O 2 at the air/water interface of aqueous droplets. However, none of these studies have investigated OH production in droplets containing nitrate (NO 3 – ) or nitrite (NO 2 – ) anions. Those two ions, in particular NO 3 –, play a key role in atmospheric chemistry. The goal of this work was to study the spontaneous production of H 2 O 2 in water droplets containing these two anions under dark conditions. Compared to ions that we have already studied (i.e., Cl – and Br – ), H 2 O 2 production in droplets containing NO 2 – or NO 3 – can be either enhanced or inhibited depending on the NO 2 – or NO 3 – concentrations. These findings suggest that, below a certain concentration, NO 2 – and NO 3 – enhance the H 2 O 2 production due to their ability to disrupt the water structure at the interface, where at larger concentrations, a specific interfacial NO 2 – or NO 3 – chemistry starts to be important, producing gas-phase species such as HONO and NO 2 . By monitoring H 2 O 2 and several other gas-phase products, we propose a mechanism to explain this specific interfacial chemistry of NO 2 – and NO 3 – . This chemistry may not be significant during day time due the photolysis of these two anions, but it can have an important impact during night time.