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

Authors: Sebnem Andreani-Aksoyoglu, Werner K. Graber, Johannes Keller

Addresses: Atmospheric Pollution, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland. ' Atmospheric Pollution, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland. ' Atmospheric Pollution, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland

Abstract: 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 NO_x (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 NO_x 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 investigated. A correlation was found between the sensitivity of O₃ to emission reductions, and NO_z (NO_y-NO_x, where NO_y = NO_x + PAN + HNO₃ + other nitrates) at the time of peak O₃. VOC controls seem to be effective only at NO_z concentrations higher than about 2 ppb, whereas NO_x controls are effective also below this range. Exclusion of biogenic VOC decreased the calculated O₃ concentrations by only 5% in certain regions. PAN and H₂O₂ concentrations, however, decreased significantly. Differences and similarities between the results of this study and those of a multi-parcel Lagrangian model are discussed, and criteria are outlined to decide on the choice for specific problems.

Keywords: biogenic VOC; volatile organic compounds; emission reduction; Lagrangian model; ozone; UAM; urban airshed model; Switzerland; photochemical smog; air pollution; environmental pollution; 3D modelling; peroxyacetyl nitrate; hydrogen peroxide; nitric acid; formaldehyde.

DOI: 10.1504/IJEP.1997.028166

International Journal of Environment and Pollution, 1997 Vol.8 No.1/2, pp.174 - 194

Published online: 15 Sep 2009 *

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