Proceedings - C-SRNWP Project

The distribution of the source terms in the UK is based on the Warren Spring Laboratories
(WSL) emission inventories (Figure 9).
Outside of the UK (Figure 10) the distribution is based on the EMEP 150 km emission
inventories, produced by the Co-operative Programme for Monitoring and Evaluation of the
Long-Range Transmission of Air Pollutants in Europe. The EMEP 150 km grid covers
roughly the same area as the NAE grid and hence should constitute a good representation of
the distribution of aerosol sources in the NAE.
The dominant source terms leading to atmospheric aerosol in the NAE model region are sea
salt, soil particles and emissions of sulphur dioxide, nitric oxide and nitrogen dioxide.
The man made emissions require some atmospheric chemistry to take place before CCN are
formed. Good emission inventories for aerosol sources are provided by WSL for both SOx
and NOx. However, under many conditions, which lead to poor visibility, as for example
radiation fog, these emissions are well above the boundary layer and do not contribute to the
local aerosol. Thus it is important that the source terms are introduced with an initial vertical
distribution.
Within the UK area, the WSL inventory has been used, with the assumptions that effective
source height is 1.5 times chimney height, to allow for plume rise. The emissions have then
been allocated to the appropriate model level.
A simple sinusoidal diurnal variation has been implemented peaking at midday, with an
amplitude that is 70% of the mean value. This diurnal variability was created to simulate the
variability of pollution from industry and transport.
Emissions have changed significantly in recent years (Figures 11 and 12) and so there is a
need to update the source data.
An additional (small) surface term has been added everywhere to allow for natural sources.
Figure 11: European sulphur emissions in Tg per year
216