Impact of urban parameterization on high resolution air quality forecast with the GEM – AQ model
1Department of Environmental Engineering Systems, Warsaw University of Technology, Warsaw, Poland
2WxPrime Corporation, Toronto, Ontario, Canada
3Centre for Research in Earth and Space Science, York University, Toronto, Ontario, Canada
Abstract. The aim of this study is to assess the impact of urban cover on high-resolution air quality forecast simulations with the GEM-AQ model. The impact of urban area on the ambient atmosphere is non-stationary and short-term variability of meteorological conditions may result in significant changes of the observed intensity of urban heat island and pollutant concentrations. In this study we used the Town Energy Balance (TEB) parameterization to represent urban effects on modelled meteorological and air quality parameters at the final nesting level with horizontal resolution of ~5 km over Southern Poland. Three one-day cases representing different meteorological conditions were selected and the model was run with and without the TEB parameterization. Three urban cover categories were used in the TEB parameterization: mid-high buildings, sparse buildings and a mix of buildings and nature. Urban cover layers were constructed based on an area fraction of towns in a grid cell. To analyze the impact of urban parameterization on modelled meteorological and air quality parameters, anomalies in the lowest model layer for the temperature, wind speed and pollutant concentrations were calculated. Anomalies of the specific humidity fields indicate that the use of the TEB parameterization leads to a systematic reduction of moisture content in the air. Comparison with temperature and wind speed measurements taken at urban background monitoring stations shows that application of urban parameterization improves model results. For primary pollutants the impact of urban areas is most significant in regions characterized with high emissions. In most cases the anomalies of NO2 and CO concentrations are negative. This reduction is most likely caused by an enhanced vertical mixing due to elevated surface temperature and modified vertical stability. Although the outcome from this study is promising, it does not give an answer concerning the benefits of using TEB in the GEM-AQ model in an operational configuration. Additional long term evaluation would be required to better estimate the anthropogenic heat flux and to assess the urban impact in longer time scales (seasonal and annual average).