Fig. 1: Enhanced HONO production from nitrate photolysis by iodide.
From: Aerosol iodide accelerates reactive nitrogen cycling in the marine atmosphere
a observed HONO concentrations during the experiments: (1) nitrate (1.0 M); (2) nitrate (1.0 M) + iodide (3.6 × 10–4 M); (3) nitrate (1.0 M) + iodide (1.8 × 10–4 M); (4) nitrate (1.0 M) + iodide (1.8 × 10–4 M) +  chloride (1.0 M); (5) nitrate (1.0 M) + iodide (1.8 × 10–4 M) + bromide (1.5 × 10–3 M); (6) nitrate (1.0 M) +  iodide (1.8 × 10–4 M) + bromide (3.0 × 10–3 M); (7) nitrate (1.0 M) + iodide (3.6 × 10–4 M) + bromide (3.0 × 10–3 M). The error bars represent the standard deviation of all conducted experiments. b HONO production when low concentrations of iodide (1.8 × 10–6 M) coexist with bromide (1.5 × 10–3 M). Initially, only molecular iodine (I2) is present (activated from iodide), with no molecular bromine (Br2), indicating that iodide is involved in nitrate photolysis. Due to the much lower concentration of iodide, the amount of HONO produced is relatively small. Once iodide is nearly depleted (with I2 rapidly declining), bromide can then participate, producing Br2, resulting in a corresponding increase in HONO production owing to the higher bromide concentration (three orders of magnitude greater than iodide). Overall, iodide dominates the production of HONO, while chloride and bromide have a relatively minor effect on HONO production in the presence of iodide.
