AQMA (Air Quality Management Area) Where a first, second and third stage review and assessment has been carried out for a pollutant and it has been concluded that the objective will not be met the Local Authority will declare its area, or part of it, an Air Quality Management Area. The Local Authority must then prepare an action plan for that area.
BENZENE A volatile organic compound (VOC). Its chemical structure is C6H6 consisting of six atoms of carbon arranged in a ring structure with six hydrogen atoms. It is a liquid at room temperature but readily evaporates. Almost all benzene found in the atmosphere at ground level in the northern hemisphere is likely to have resulted from human activities especially from the combustion of petrol in vehicle engines. The proportion of benzene in petrol is about 2% by volume in the UK. Can cause some forms of cancer.
BTX Benzene, xylene and toluene. Monitoring for these pollutants is carried out using diffusion tubes. Xylene and toluene are not pollutants dealt with under Air Quality Regulations 1997.
1,3-BUTADIENE A chemical compound comprising four carbon and six hydrogen atoms. Trace amounts can be found in the atmosphere. Derives mainly from combustion of petrol in motor vehicle engines. Also used in industry, mainly in the production of synthetic rubber for tyres. Can cause a variety of cancers.
CANYON Where a road is enclosed on both sides by tall buildings that form a continuous barrier, the road becomes at the bottom of a canyon. This results in poor dispersion of pollutants by wind etc. and levels of pollution may be abnormally high in the canyon.
CARBON MONOXIDE (CO) A gas produced in the process of combustion, including motor car engines, domestic heating appliances, cigarettes, or even forest fires. Out doors the main sources of carbon monoxide are vehicle exhausts. The threat to health is a reduction in the oxygen carrying capacity of the blood that may increase the risk of problems in individuals with ischaemic heart disease.
DIFFUSION TUBE MONITORING An inexpensive and simple technique used to monitor pollutants. A metal or plastic tube containing an absorbent is placed outside and left for a period of days or weeks. The pollutant of interest is then absorbed continuously over the exposure period. The tubes are analysed to find out how much pollutant has been absorbed. The result can only give a measure of the average concentration of pollutant over the exposure period. Pollution episodes giving short term high levels of a pollutant will not be detected.
FINE PARTICLES (PM10) Particles with a diameter of 10 micrometers or less are referred to as PM10 (particulate matter less than 10 micrometers in diameter). Particles of this size and below are particularly important because they penetrate deep into human lungs carrying with them the surface coatings which include many organic chemicals. There is a documented relationship between levels of PM10 particulates and rates of disease and death.
LEAD An element that has been known for centuries to be harmful to people working with it. Lead can be released naturally through various processes but also from mans activities. Estimated emissions of lead for 1995 are that 1,067 tonnes were emitted and that this represents 73% of the total lead emitted. Low levels of lead ingestion have effects on the central nervous system and in particular, on the developing brain of children.
MICROGRAM One microgram (1mg) is one millionth of a gram (1/1,000,000 of a gram). There are one thousand micrograms in a milligram and one thousand milligrams in a gram.
MICROMETER One micrometer (1mm) is one millionth of a metre (1/1,000,000 of a metre).
MILLIGRAM One milligram (1mg) is one thousandth of a gram (1/1,000 of a gram).
MODELLING A technique for predicting what concentration of a pollutant will occur at a particular place. It relies on being given information about the source of a pollutant (either assumed or measured), and then assuming that it is dispersed in a particular way that can be described mathematically. The more complex models are often run on computers. Models can be reasonably accurate when describing the dispersion of a single pollutant from a single point source. Other models, even sophisticated ones, can have large margins of error (± 100% or worse).
ng/m3 Nanograms per cubic metre. This is one thousand millionth of a gram per cubic metre. This is an expression of the weight of a pollutant per cubic metre of air. There are one thousand nanograms in a microgram.
ug/m3 Micrograms per cubic metre. Can also be written as mgm-3. This is an expression of the weight of a pollutant per cubic metre of air. There are one thousand micrograms in a milligram.
NANOGRAM One nanogram is one thousand millionth of a gram. There are one thousand nanograms in one microgram, one thousand micrograms in a milligram and one thousand milligrams in a gram.
NITROGEN DIOXIDE Nitrogen dioxide (NO2) is a gas produced by the reaction of nitrogen and oxygen in combustion processes. There are natural sources but the largest source in the U.K. is from the combustion of fossil fuels by motor transport and non-nuclear power stations.
NOX A general term for the oxides of nitrogen including nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O).
OZONE Ozone (O3) is a special form of oxygen consisting of three oxygen atoms per molecule. It is not emitted directly from any man-made source in any significant quantities but arises from chemical reactions driven by sunlight in the atmosphere. Ground level (tropospheric) ozone pollution should not be confused with the ozone layer which exists in the higher atmosphere (stratosphere). Ground level ozone is itself a pollutant and at high levels may lead to respiratory symptoms. It also leads to the formation of other pollutants. Ozone is not included in Local Authority Reviews and Assessments.
PPB Parts per billion. One ppb is one part in 1,000,000,000 parts by volume. This is an expression of the concentration of a pollutant in air. The relationship between ug/m3 and ppb will vary according to the pollutant being dealt with.
PPM Parts per million. One ppm is one part in 1,000,000 parts by volume. This is an expression of the concentration of a pollutant in air. The relationship between ug/m3 and ppb will vary according to the pollutant being dealt with.
REAL TIME MONITORING (or CONTINUOUS MONITORING) A monitoring technique whereby an automated analyser sucks in air, analyses it, records the result and then analyses a new sample of air. The analysis usually takes a matter of seconds so that hourly or shorter term averages can be calculated. The results are therefore available almost immediately rather than with diffusion tubes which have to be sent to a laboratory for analysis with the results becoming available only days or weeks later. This technique is more accurate than diffusion tube monitoring and is able to detect short term peaks of pollution.
SULPHUR DIOXIDE Sulphur dioxide (SO2) is a gas which dissolves in water to give an acidic solution that is readily oxidised to sulphuric acid. Natural sources include volcanic activity and from marine organisms. In the U.K. the predominant source is from the combustion of sulphur containing fossil fuels, principally coal and heavy oils.
TRANSBOUNDARY POLLUTANT A pollutant which travels beyond national boundaries is termed a transboundary pollutant. Action by the country which the pollutant effects, but from which it did not originate, will not be effective in solving the problem.
VOC Volatile organic compound such as benzene or 1,3-butadiene.
