Heterogeneous reaction of NO2: Characterization of gas-phase and adsorbed products from the reaction, 2NO(2)(g)+H2O(a)-> HONO(g)+HNO3(a) on hydrated silica particles

This study provides the first in-situ characterization of the products in t he heterogeneous reaction 2NO(2)(g) + H2O(a) --> HONO(g) + HNO3(a). Transmi ssion FT-IR spectroscopy and UV-vis spectroscopy were used to probe the het erogeneous chemistry of gas-phase nitrogen dioxide on hydrated SiO2 particl es. At 298 K, gaseous nitrogen dioxide reacts with adsorbed water on the su rface of SiO2 particles to form adsorbed nitric acid and gas-phase nitrous acid. FT-IR spectroscopy of the hydrated SiO2 surface following reaction wi th NO2 provides definitive identification of the adsorbed nitric acid produ ct. The reaction does not occur when gas-phase nitrogen dioxide is reacted on dehydrated silica particles. The gas-phase product nitrous acid was dete cted with both FT-IR and UV-vis spectroscopy. Although homogeneous and hete rogeneous reactions can contribute to die observed HONO signal, flow cell m easurements can be used to distinguish between heterogeneous and homogeneou s reaction pathways leading to HONO production.