It is impracticable to measure every emission source in a large urban area, with a population of millions. The majority of emissions are therefore estimated from other local information such as fuel consumption, vehicle kilometres travelled (VKT), or some other measure of activity relating to the emissions. Emission factors, derived from the results of measurements, are then applied to the activity data in order to estimate the likely emissions.
A 1998 UK government action plan will address all aspects of the Local Air Pollution Control system (LAPC). The plan includes action: to develop a more consistent approach to inspection of air pollution across the country; to actively encourage local authorities to sign up formally to the Cabinet Office's Enforcement Concordat and to produce and implement clear policies relating to all their enforcement functions, including LAPC; to monitor centrally local authority action to undertake four year reviews of authorisations; by the Chartered Institute of Environmental Health and the Local Government Association, to produce a management guide for local authorities on LAPC; to secure compliance by metal and plastic coating processes. A helpline has been set up to advise Local Authorities on technical compliance issues relating to this sector; and to consolidate and develop the 'link authority' scheme for local authority networking on LAPC issues within the UK.