Combustion sources

Combustion processes are an important source of a range of air pollutants as follows;?? Carbon monoxide (CO),?? Nitrogen dioxide (NO2),?? Sulphur dioxide (SO2),?? Particulates and associated inorganic and organic chemicals,?? Organic vapours e.g. formaldehyde, acetaldehyde, and benzene.Sources of these are present in both ambient and indoor environments. In Europeancountries emissions from major anthropogenic sources are controlled by legislation.This includes regulation of industrial emissions (e.g. Directive on Integrated PollutionPrevention and Control, Large Combustion Plant Directive) and emissions from motorvehicles including directives arising from the Auto/Oil programme (e.g. emissionlimits defined by Euro 4 for CO, hydrocarbons and nitrogen oxides from petrolfuelled vehicles, and additionally particles from diesel fuelled vehicles under ECDirective 98/69/EC), and limits on the sulphur content of some liquid fuels and thebenzene content of petrol. Under the Air Quality Limit Values Regulations memberstates are required to take necessary measures to ensure that air quality limit valuesare not exceeded by defined dates in zones that have a population of more than250,000. Table 1 summarises objectives for England set out in the Air QualityRegulations. Also, under the EU strategy to combat acidification national emissionceilings have been set for SO2, nitrogen oxides, volatile organic compounds (VOCs)and ammonia.The concentrations present in the ambient air provide a baseline for the level ofpollutant found indoors as this air enters indoors by processes of infiltration andventilation. However the concentration indoors will be modified by processes ofsorption to surfaces and chemical reaction depending on the chemical and physicalproperties of the pollutant and internal surfaces. Also sources of these pollutantsindoors will result in direct emissions to the indoor environment and resultingconcentrations will depend upon rates of emission, dilution by internal space andremoval by air exchange with the outside.