Occurrence of nitric acid and related compounds in the Northern Vienna basin during summertime anticyclonic conditions

Atmospheric concentrations of ozone, nitric acid and particulate nitrites were measured during photochemically active periods in summer 1986 and 1987 near Vienna, Austria. Field data were taken on tower stations at different levels. On a summit 575 m asl and 10 km downwind of Vienna peak 4-h averages of 139 ppb ozone, 5.1 ppb nitric acid and 3.3 ppb ammonium nitrate were recorded in the urban plume at noon. Eighty-six per cent of daytime concentrations of ozone and 66% of daytime nitric acid were found to be present in the consecutive night in the mixed layer above an inversion indicating that it can act as a reservoir for reactive photochemical pollutants. In the late evening hours a slight increase in concentration of HNO3 was observed at tower stations, which can be attributed to a nighttime formation.