Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in Southern China

摘要

We performed measurements of nitrous acid (HONO) during the PRIDE-PRD2006campaign 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 instrumentwhich was setup in one of the campaign supersites along with a variety ofinstruments measuring hydroxyl radicals, trace gases, aerosols, andmeteorological parameters. Maximum diurnal HONO mixing ratios of 1–5 ppbwere observed during the nights. We found that the nighttime build-up of HONOcan be attributed to the heterogeneous NO₂ to HONO conversion on groundsurfaces and the OH + NO reaction. In addition to elevated nighttime mixingratios, measured noontime values of ≈200 ppt indicate theexistence of a daytime source higher than the OH + NO→HONO reaction. Using thesimultaneously recorded OH, NO, and HONO photolysis frequency, adaytime additional source strength of HONO (P_M) was calculated to be0.77 ppb h?1 on average. This value compares well to previousmeasurements in other environments. Our analysis of P_M provides evidencethat the photolysis of HNO₃ adsorbed on ground surfaces contributes to theHONO formation.