Three–dimensional modelling of photochemical air pollution in Switzerland and comparison with a multi–parcel Lagrangian model

The photochemical smog situation in Switzerland on 29 July, 1993 was simulated using the 3–D grid model UAM (Urban Airshed Model) and the results were compared with those of a multi–parcel Lagrangian model. Sensitivity analyses concerning initial conditions, emissions, deposition, biogenic volatile organic compounds (VOC), and emission reductions were carried out. Results were compared with field measurements. Calculations showed that although ozone (O3) formation in Switzerland is mainly NOx (NO + NO2) limited, some areas seem also to be sensitive to VOC emissions. According to the calculations, reducing anthropogenic VOC emissions by 20–80% would lead to a decrease of 5–25% in O3 levels in a few regions, whereas the calculated decrease in O3 concentrations by NOx emission reductions was 6–38% and is expected to be effective over a larger area. Impacts of emission reductions on other species, such as peroxyacetyl nitrate (PAN), hydrogen peroxide (H2O2), nitric acid (HNO3) and formaldehyde (HCHO) were inv...