Keywords: nitrogen dioxide, particulate matter, transfer functions, source-receptor modelling, Gaussian plume model, complex terrain, population exposure, dispersion modelling, Switzerland, air pollution, air quality, emission inventories
Applied comprehensive NO2 and particulate matter dispersion modelling for Switzerland
This paper presents the NO2 and Particulate Matter (PM) dispersion modelling for the whole of Switzerland. Air quality maps are computed for the year 2000 and future years. Future developments like the EURO-4 legislation on motor vehicles are taken into account. For all major source groups (road traffic, off-road traffic, industry, households, etc.), separate countrywide emission inventories with a spatial resolution of 200 m are used. Dispersion modelling is performed by applying transfer functions to each cell of every inventory. These functions have been computed with a Gaussian plume model using several years of hourly meteorological data. Different functions reflect the source group characteristics (emission height, time series of emission strength, etc.) and the micro-climatology (for three Swiss regions: Swiss Plateau, alpine valleys and remaining part of Switzerland). In the Alpine valleys, the transfer functions are aligned to the main wind direction in order to better reflect the dispersion conditions in mountainous terrain. Emission and dispersion modelling is performed for NOx at first; the NO2 concentration is then estimated using a parameterised oxidation function. For PM, primary particles up to 2.5 µm, primary particles in the size range 2.5-10 µm, secondary particles from gaseous precursors and the imported background concentration are modelled separately and then summed up. The predicted concentration level for 2000 is validated using measurements from monitoring stations. A good agreement is found. In 2000, 1.2% (505 km²) of the total surface of Switzerland exhibits a mean NO2 concentration above the 30 µg/m³ air quality standard (grid cell average). In this area, 25.0% of the population (1.72 million persons) have their home location. In 2000, ca. 5.5% (2300 km² of the land surface are exposed to concentrations above the air quality standard of 20 µg/m³ for PM10; 41.3% of the population lives there.