Insight Into How Air Quality Standard Came Into Being

Water and air quality guidelines and standards often are developed and used in a manner that is disconnected from their original intended purpose, with the scientific reason for each standard being forgotten. The goal of this assignment is to investigate and explain the underlying reasons behind the allowable limits and threshold values of specific water and air quality parameters.

How Air Quality Standard Came Into Being?

Sulphur dioxide is a compound made up of two oxygen atoms and one sulphur atom. Sulphur in physical form is yellow odourless solid which is insoluble in water. Sulphur dioxide is one of the prominent compounds of sulphur. At room temperature sulphur dioxide is a colourless gas with a suffocating choking odour. The effect of releasing sulphur dioxide in atmosphere causes acid rain and photochemical smog.

Sulphur dioxide is present in the environment through various natural and anthropogenic sources. In nature sulphur dioxide is being produced as a result of vegetation fires, volcanic emissions, ocean spray and foam, and by the action of microbial on sulphurous substances. (Fellenberg, 1997).

Anthropogenic sources of sulphur dioxide is produced by burning of fossil fuels, extraction of metals from ores and from various branches of chemical industry. Combustion of coal is of particular concern as there is about 1-9% of sulphur present (Baird, 1998). Considering the amount of fossil fuels that are being burnt all over the world particularly to generate electricity. The amount of sulphur dioxide being emitted by man-made sources is more significant than natural sources. Anthropogenic source is significant because 1) natural sources such as volcanic emissions the sulphur dioxide is shot high into the atmosphere 2) one property of SO2 in atmospheric conditions is that the gas disintegrate after two weeks. Therefore, SO2 cannot spread globally or affect the human population as suggested by (Fellenberg, 1997).

In the 1900s events that unfolded in Donora, Pennsylvania and the infamous London Smog of prompted Governments to take proactive steps to reduce air pollution. Since these events Governments/Organizations introduced many regulations to control point sources of many of the chemicals that were believed to cause deleterious effect on the environment and human health. Initially, after the London smog a series of regulations and acts such as Clean Air Act of 1956 and 1968 were promulgated (in UK). However, these acts did not place any limits to various pollutants being discharged into the air. The first time limits and guide values were used for specific pollutants was in Air Quality Standard Regulation 1989. Over the years these standards got refined and revised and currently Air Quality Standards Regulation of 2010 is being followed.

According to the Air Quality Standards Regulation of 2010 (AQRS, 2010 No. 1001) the allowable limit for SO2 is 350 μg/m3 measured as mean concentration for an hour and this should not exceed 24 times a calendar year. The concentration of SO2 should not exceed 125 μg/m3 measured as a mean concentration for 24 hours and this should not exceed more than three times a year. The alert threshold for SO2 is 500 μg/m3 over an area of 100 km2 or an entire zone whichever is smaller. It is to note that these values are derived from National Air Quality Strategy of 2000 and almost all of the values are the same.

These criteria levels were set by reviewing numerous studies on the effects of air pollution. In UK, these values were based on the assessment of Expert Panel on Air Quality Standards (EPAQS). These threshold values were worked out by observing the effect of the SO2 concentration on human health and environment. The main focus while establishing the criteria level was that the SO2 concentration should be so low that it has the minimum effect on human health. Basically, the mechanism of toxicity associated with SO2 is that when inhaled there is a “decreased airflow due to airway constriction, altered mucocilliary and effects on alveolar macropahage activity” as stated by USEPA (1986). Ware (1981) reviewed the pollution episode of London 1975 and found out as “maximum concentration of SO2 reached more than 944 μg/m3 an increase in 100 to 200 deaths above expected totals was observed during the week in which the episode”. Even when the SO2 concentration exceeded 500 μg/m3 for more than 24 hours there was increase daily mortality (USEPA, 1986). Similar case was observed by Knelson (1978), when daily mean levels (of SO2) reached 119-249 μg/m3 the elderly and asthmatic people had an increase in illness. Moreover, Sunyer (2003) observed there was increase in hospital admission for Ischemic Heart Disease for every 10 μg/m3 increase in SO2 concentration from the average value of that particular place. This pattern was seen in 7 mega cities around the world. So a clear link can be seen between the increase of mean concentration of SO2 in the air and the rise in morbidity of people. To gauge the long term effect of SO2 concentration on humans several studies showed two communities with different SO2 levels in the air i.e. one with a SO2 concentration in the range of 68-275 µg/m3 and the other community in the range of 10–123 µg/m3. The results showed that the community with clean air had low respiratory illnesses and small or no reduction in lung function (WHO, 2000).

Mudd and Kozlowski (1975) pointed out that Sulphur Dioxide can effect plants depending upon the reaction of SO2 with the solution. So, the key reaction that determines the effect is the degree of oxidation of SO2 into sulphate. The most common type of injury that a plant gets due to SO2 is intraveinal chlrosis.


In conclusion it can be said that the National Air Quality Strategy (NAQS, 2000) have a clear scientific rationale behind the parameter limits. Furthermore, SO2 levels have dropped considerably over the years since the implementation of the strategy. DEFRA statistical release (2014) states that from 2009 till now an average of 0.41 million tonnes SO2 is decreased annually. Based on the evidence I feel the allowable limit of SO2 is appropriate and consistent with evidence present.

List of References –

  • Gunter Fellenberg, 3rd Edition, 1997, The Chemistry of Pollution.
  • Colin Baird 2nd Edition, 1998, Environmental Chemistry.
  • Air Quality Standards Regulation of 2010 (AQRS, 2010 No. 1001)
  • Second Addendum to Air Quality Criteria for Particulate Matter and Sulfur Oxides (1982): Assessment of Newly Available Health Effect Information, EPA/600/8-86/020F December 1986
  • J H Ware, L A Thibodeau, F E Speizer, S Colome, and B G Ferris, Jr, 1981. Assessment of Health effects of atmospheric sulphur oxides and particulate matter: evidence from observational studies. Environ Health Perspect 41; 255-276.
  • John H Knelson, 1978, Evidence for the Influence of Sulfur Oxides and Particulates on Morbidity, Bull N Y Acad Med. 54(11): 1137–1154.
  • Jordi Sunyera, Ferran Ballesterb , Alain Le Tertrec , Richard Atkinsond , Jon G. Ayrese , Francesco Forastieref , Bertil Forsbergg , Judith M. Vonkh , Luigi Bisantii , Jose´ M. Tenı´asb , Sylvia Medinac , Joel Schwartzj , Klea Katsouyannik, 2003, The association of daily sulfur dioxide air pollution levels with hospital admissions for cardiovascular diseases in Europe (The Aphea-II study), European Heart Journal (2003) 24, 752–760.
  • Air Quality Guidelines for Europe 2000, 2nd Edition, WHO regional Publications, European Series, No 91.
  • B Mudd and T.T Kozloskwi, 1975, Responses of Plants to Air Pollution, London.
  • Department of Environment, Food & Rural Affairs, Defra National Statistics Release: Emissions of air pollutants in the UK, 1970 to 2013.

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