1College of Environmental Sciences and Engineering, Peking University, Beijing, China
2Institute for Energy and Climate Research, Troposphere (IEK-8), Research Center Jülich, Jülich, Germany
3Max Planck Institute for Chemistry, Biogeochemistry Department, Mainz, Germany
4Leibniz Institute for Tropospheric Research, Leipzig, Germany
5Research Center for Advanced Science and Technology, University of Tokyo, Japan
Abstract. 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 meteorological parameters. Maximum diurnal HONO mixing ratios of 1–5 ppb were observed during the nights and are among the highest ever reported. We found that the nighttime build-up of HONO can be attributed to the heterogeneous NO2 to HONO conversion on ground surfaces and the OH + NO reaction. In addition to the high 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 simultaneously recorded OH, NO, and HONO photolysis frequency, a daytime additional source strength of HONO (PM) was calculated to be 0.77 ppb h−1 on average. This value compares well to previous measurements in other environments. Our analysis of PM provides evidence that the photolysis of HNO3 adsorbed on ground surfaces contributes to the HONO formation.