Detection of nitrous acid in the atmosphere by differential optical absorption

Abstract

HNO 2 was investigated by long path optical absorption at three sites in Western Europe. It vas definitely identified and measured in moderately polluted air at Jülich. Mixing ratios as high as 0.8 ppb were observed before sunrise. After sunrise the HNO 2 is photolyzed and considerable amounts of OH are produced. The formation of HNO 2 is unclear and possible reactions are discussed.