| Gas-phase nitrous acid (HONO) is a component of reactive nitrogen species (NOy) in the atmospheric boundary layer, and its environmental significance relies on its fast photolysis under solar radiation forming a strong daily hydroxyl (OH) radical source, especially during the morning time. Researches of HONO in atmospheric chemistry are focused on the sources of this species because its formation mechanisms in natural environment has not been completely revealed by now. In this work, measurements of ambient HONO, as well as gaseous nitric acid (HNO3), which is necessary for the research, were performed in five field studies at the sites with different levels of anthropogenic pollutions to investigate deeply the fate of HONO in the lower atmosphere. The field studies are two campaigns in a typical metropolitan area in summer 2001 and winter 2004, two at a forested rural site in summers of 2000 and 2003, and one at a rural mountain site in summer 2002. Additional designed experiments related to HONO production were conducted both during field campaigns and in our laboratory.; Based on the data collected during the studies, tropospherc chemistry of HONO is further understood---Heterogeneous reactions between NOx (NO + NO2) and water vapor on ground surfaces are major contributors to urban and nocturnal rural HONO; trapped nitrite in solutions, such as dew water, on foliage surfaces can provide a morning HONO source through evaporation in vegetated areas; photolysis of HNO3 deposited on moisturized surfaces might be another effective daytime source of HONO in both less polluted and polluted atmospheres; and HONO photolysis obtains more credits in the production of OH radicals, thus in the oxidation cycles, in the troposphere. |
