Surprisingly small HONO emissions from snow surfaces at Browning Pass, Antarctica
Measured Fluxes of nitrous acid at Browning Pass, Antarctica were very low, despite conditions that are generally understood as favorable for HONO emissions, including: acidic snow surfaces, an abundance of NO<sub>3</sub><sup>-</sup> anions in the snow surface, and abundant UV light for NO<sub>3</sub><sup>-</sup> photolysis. Photochemical modeling suggests noon time HONO fluxes of 5–10 nmol m<sup>-2</sup> h<sup>-1</sup>; the measured fluxes, however, were close to zero throughout the campaign. The location and state of NO<sub>3</sub><sup>-</sup> in snow is crucial to its reactivity. The analysis of soluble mineral ions in snow reveals that the NO<sub>3</sub><sup>-</sup> ion is probably present in aged snows as NaNO<sub>3</sub>. This is peculiar to our study site, and we suggest that this may affect the photochemical reactivity of NO<sub>3</sub><sup>-</sup>, by preventing the release of products, or providing a reactive medium for newly formed HONO. In fresh snow, the NO<sub>3</sub><sup>-</sup> ion is probably present as dissolved or adsorbed HNO<sub>3</sub> and yet, no HONO emissions were observed. We speculate that HONO formation from NO<sub>3</sub><sup>-</sup> photolysis may involve electron transfer reactions of NO<sub>2</sub> from photosensitized organics and that fresh snows at our site had insufficient concentrations of adequate organic compounds to favor this reaction.