Snowpack photochemical production of HONO: a major source of OH in the Arctic boundary layer in springtime

Both snow manipulation experiments and ambient measurements during the Pola r Sunrise Experiment 2000 at Alert (Alert2000) indicate intensive photochem ical production of nitrous acid (HONO) in the snowpack. This process consti tutes a major HONO source for the overlying atmospheric boundary layer in t he Arctic during the springtime, and sustained concentrations of HONO high enough that upon photolysis they became the dominant hydroxyl radical (OH) source. This implies a much greater role for OH radicals in Arctic polar su nrise chemistry than previously believed. Although the observations were ma de in the high Arctic, this finding has a significant implication for the b oundary layer atmospheric chemistry in Antarctica during sunlit seasons and in the mid to high latitudes of the Northern Hemisphere during the winter and spring seasons when approximately 50% of the land mass may be covered b y snow.