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Compared with the point and line
sources in the city the background sources contribute a small proportion of the
total emissions. It is easiest to consider them as grid sources.
Grid
sources are used in ADMS – Urban to represent aggregated sources that need not
be modelled explicitly as point or line sources. This helps to speed up run
time and to enable the “intelligent gridding” option.
Grid sources can also be used to represent “background” emissions, i.e. domestic
heating, small industry etc.
ADMS –
Urban automatically subtracts explicitly modelled sources from the grid
sources, so even the explicitly modelled sources must be included in the grid
sources. Models run for the review and assessment process in Bristol to
calculate the situation now and in the future used a
combination of background source data and road and point sources that were not
modelled explicitly.
Background Contribution
The background data were taken from the National
Atmospheric Emissions Inventory (NAEI) data set available on the Internet www.naei.org.uk .The area of each grid
square was 1 square kilometre.
NAEI
data is for 1996. There
is an assumption that there will be negligible change in the
nature and amount of these emissions. The data from the NAIE are broken down by sector, i.e. roads,
small industry, domestic and other. All sectors apart from roads were summed
and the emissions from these are used
as the background sources.
Bristol City Council received an emissions inventory from
the London Research Centre (LRC) in 1997. The
NAEI data were used in preference to the data from LRC for this
study, as the approach adopted required a wider spatial coverage than that
available from the LRC data set.
The data files for NOx and PM10
were processed in a spreadsheet such that the emissions were converted to grams
per second per square kilometre from tonnes per year. The area of interest was
extracted using GIS functions.
1.1.1.1Domestic
Sources
Domestic sources of NOx and PM10 are included in the
background sources from the NAEI. As Bristol is a
smoke control area, we have not included additional sources of PM10. Although
illegal domestic combustion of non-smokeless fuels and bonfires
undoubtedly contributes to PM10 concentrations in parts of the city,
we have no data with which to assess the
impact of these
sources. |