GASEOUS AND PARTICULATE OXIDIZED AND REDUCED NITROGEN SPECIES IN THE ATMOSPHERIC BOUNDARY-LAYER IN SCANDINAVIA IN SPRING

Observations of the concentration of several nitrogen containing compo unds at five rural Scandinavian sites during March-June 1993 are repor ted. Total nitrate NO3- + HNO3) and total ammonium (NH4+ + NH3) were m easured by denuder and filter pack. In general the methods agree well. At all sites the particulate fraction dominated, with the largest fra ction of NO3- and the lowest of NH4+ at the sites which were closest t o the emission sources. The fraction of NO3- of total nitrate increase d with increasing NO2 concentrations, indicating that the nighttime co nversion of NO2 to NO3- is an important route of formation for NO3-. A positive correlation was found between HNO3 and O-3 in June at all si tes, while no correlation was found early in the spring. Model calcula tions were made with a lagrangian boundary layer photooxidant model fo r the whole period, and compared to the measured concentrations. The c alculated ratio between mean observed and modelled daily maximum conce ntrations of ozone over the measurement period were within +/-10% at a ll sites. The models ability to describe the daily ozone maximum conce ntration was satisfactory with an average deviation of 19-22% from the observed concentrations. HNO3 was underestimated by over 50% at all s ites except the one closest to the emission sources. The correlation b etween modelled and observed concentrations was generally best for the sites with shortest transport distance from the sources of emission.