Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> Organic nitrates (RONO<sub>2</sub>) are secondary compounds whose fate is closely related to the transport and removal of NO<sub>x</sub> in the atmosphere. Despite their ubiquitous presence in submicron aerosols, the photochemistry of RONO<sub>2</sub> has only been investigated in the gas phase, leaving their reactivity in condensed phases poorly explored. This work aims to address this gap by investigating, for the first time, the reaction products, and the mechanisms of aqueous-phase photolysis of four RONO<sub>2</sub> (i.e., isopropyl nitrate, isobutyl nitrate, α-nitrooxyacetone, and 1-nitrooxy-2-propanol). The results show that the reactivity of RONO<sub>2</sub> in the aqueous phase differs significantly from that in the gas phase. In contrast to the gas phase, where RONO<sub>2</sub> releases NO<sub>x</sub> upon photolysis, the aqueous phase photolysis of RONO<sub>2</sub> leads primarily to the direct formation of HONO, which was confirmed by quantum chemistry calculations. Hence, the aqueous-phase photolysis of RONO<sub>2</sub> represents both a NO<sub>x</sub> sink and a source of atmospheric HONO, a significant precursor of âOH and âNO. These secondary radicals (·OH and ·NO) are efficiently trapped in the aqueous phase, leading to the formation of HNO3 and functionalized RONO<sub>2</sub>. This reactivity can thus potentially contribute to the aging of Secondary Organic Aerosol (SOA) and serve as an additional source of aqueous-phase SOA.
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