[Analysis of HONO Concentration and Source in Typical Rural Area of North China]

Nitrous acid (HONO) is easily photolyzed with the production of·OH, which plays an important role in the formation of regional secondary pollution. In China, research of HONO observation is concentrated mainly in urban areas and is rarely reported in rural areas. In our study, a one-month HONO field observation was conducted at the Station of Rural Environment, Chinese Academy of Sciences (Dongbaituo Village, Wangdu County, Hebei Province) in November 2017 using the long path absorption photo meter (LOPAP). The concentration, variety characteristics, and budget of HONO was studied. During the observation period, HONO exhibited pronounced diurnal variation with low concentrations in the day and high concentration in the evening. The highest concentration at night was about 3.70×10^-9, and the lowest concentration at noon was about 0.10×10^-9, indicating the presence of a strong source of HONO in rural areas. The CO concentration increased significantly before and after heating, whereas the HONO concentration did not change significantly, indicating that heating combustion contributed less to HONO, Direct emission of motor vehicles at night contributed 23.20% and 31.20% to HONO in polluted and clean weather conditions, respectively, indicating the presence of strong sources of HONO in polluted weather conditions. The average formation rate of HONO at night from homogeneous reaction of·OH and NO could reach 0.40×10^-9 h^-1, which is 0.67 times higher than that of heterogeneous reaction of NO₂ (0.24×10^-9 h^-1), indicating that the homogeneous reaction of·OH and NO is the main source of HONO at night. HONO has a strong unknown source in the daytime with an intensity reaching 1.37×10^-9 h^-1, which contributes about 50% to HONO.