Effects of landuse heterogeneities on air quality over London
Tropospheric ozone is harmful to health and the environment. It is created over regional scales through photolytic reactions involving a complex mixture of air pollutants including nitrogen oxides (NOx) and volatile organic compounds (VOCs). The reaction of ozone with nitric oxide (NO) (mainly emitted from road transport and industry) is also important in urban areas as it leads to the formation of nitrogen dioxide (NO2) which also harmful to human health. Land cover plays a critical role in influencing the surface boundary layer processes, which in turn affect parameters such as heat flux, temperature and wind speed. Hence, it is important to have the correct treatment of land cover in mesoscale models. Our research has led to the first application of the MM5/CMAQ modelling system to simulate the distribution of ozone over London.
MM5 predicted sensible heat flux using two datasets of land cover. Left panel shows the MM5 predictions over London using USGS data and the right panel shows the predictions using CEH data (on 21 February 2003 at 14 UTC). The higher resolution CEH data shows dramatic changes over inner and outer London areas, which are not observed using the USGS data. The use of CEH data leads to lower temperatures and higher wind speeds in suburban regions of London.
MM5/CMAQ predictions of ozone (O3) concentrations over London showing the effect of using USGS (left) and CEH (right) land cover data (on 12 July 2003 at 18 UTC). Different land cover data will show changes in the predicted local meteorological parameters (such as temperature, wind speed and wind direction) and biogenic emissions. The choice of land cover can thus lead to very different modelled ozone distributions over London.
Acknowledgements & collaborations:
This research was funded by the Thai Government and the European Commission (FUMAPEX FP5 project). BADC and DEFRA are thanked for providing access to meteorological and air quality data respectively. The collaboration of the UK Met Office is also appreciated.
Selected references:
Sokhi, R. S., R. San José, N. Kitwiroon, E. Fragkou, J. Pérez, and D. R. Middleton, 2006. Prediction of ozone levels in London using the MM5-CMAQ modelling system, Environ. Modelling & Software 21, 567-577.
Kitwiroon, N., 2006. Treatment of surface boundary layer parameters for modelling air quality in urban regions. Ph.D. thesis, University of Hertfordshire, UK.