Atmos. Chem. Phys. Atmospheric Chemistry and Physics, vol. 12 (2012) pp. 1497-1513
We performed measurements of nitrous acid (HONO) during the PRIDE-PRD2006 campaign in the Pearl River Delta region 60 km north of Guangzhou, China, for 4 weeks in June 2006. HONO was measured by a LOPAP in-situ instrument which was setup in one of the campaign supersites along with a variety of instruments measuring hydroxyl radicals, trace gases, aerosols, and meteorolog-ical parameters. Maximum diurnal HONO mixing ratios of 1–5 ppb were observed during the nights. We found that the nighttime build-up of HONO can be attributed to the heterogeneous NO 2 to HONO conversion on ground surfaces and the OH + NO reaction. In addition to ele-vated nighttime mixing ratios, measured noontime values of ≈200 ppt indicate the existence of a daytime source higher than the OH + NO→HONO reaction. Using the simultane-ously recorded OH, NO, and HONO photolysis frequency, a daytime additional source strength of HONO (P M) was calculated to be 0.77 ppb h −1 on average. This value com-pares well to previous measurements in other environments. Our analysis of P M provides evidence that the photolysis of HNO 3 adsorbed on ground surfaces contributes to the HONO formation.
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