Airborne measurements of atmospheric aerosol particles and trace gases during photosmog episodes over the Swiss Plateau and the Southern Pre-Alpine Region

The concentration of atmospheric aerosol particles, primary and secondary trace gases as well as meteorological parameters were obtained from aircraft measurements in July 1993 over the Swiss Plateau and the Southern Pre-Alpine Region as part of the POLLUMET (POLLUtion and METeorology) study. On sunny afternoons, the spatial distribution of particles in the size range 0.12–3.12 μm showed a good agreement with those of secondary pollutants O3 and NOz (=NOy−NO2−NO; NOy: total odd nitrogen) in the well mixed planetary boundary layer but poor correlation with the distributions of primary pollutants NO2 and CO. The results indicate that under conditions of high air pollution and strong photochemical activity the aerosol particles mainly grow by means of secondary processes (heterogeneous nucleation) into the diameter range 0.12–1.5 μm. On the other hand, the distribution of the CN particle concentration (0.01–3 μm) was similar to the NO2 concentration indicating that CN mainly consisted of primary particles.