ON THE ORIGINS OF NIGHTTIME NO AT A RURAL MEASUREMENT SITE

Mixing ratios for NO and NO//2 were measured during 1980/1981 at Deuselbach, a rural site in Germany. The data are analyzed with regard to the occurrence of nocturnal NO signals and their origins. Anthropogenic influences arising from road traffic and home heating activities are identified by their dependence on wind direction. An additional non-directional component is found to exist. It shows up most frequently in summer and when it occurs, the NO mixing ratio increases with rising temperature indicating a biological origin of night-time NO. The temporal behavior of night-time NO is usually correlated with that of CO//2 but anticorrelated to that of O//3. This shows that NO is brought upwards to the air intake of the NO//x monitor from lower levels and that the source of the non-directional component of nocturnal NO is the earth's surface. The release of NO from soils is known from other work and this process is probably also responsible for the present observations. A flux estimate agrees with soil fluxes reported by other authors. Additional study results are discussed.