Despite the decline in sulphur dioxide in UK air over the last fifty years there are still occasions when sulphur dioxide concentrations may be high enough to affect people's health, particularly asthmatics and the elderly
In the UK sulphur dioxide gas (SO2) is largely emitted from industrial sources including power stations. The contribution from motor vehicle exhausts has been much reduced probably due to the use of low sulphur fuels.
Sulphur dioxide irritates the lining of the airways and can cause coughing, tightness in the chest and the narrowing of the airways, constricting the bronchi and bronchioles/reducing air flow
People with asthma are particularly sensitive to sulphur dioxide. The narrowing of the airways is triggered at much lower levels of sulphur dioxide than in people without asthma, and is more marked. When levels are high, asthmatics may therefore find breathing more difficult and, during pollution episodes, levels of sulphur dioxide may trigger asthma attacks.
The effects of sulphur dioxide may occur very rapidly and this has led to air pollution standards for sulphur dioxide being defined with very short averaging times: 10 or 15 minutes in addition to the more usual averaging time of 24 hours.
Calculating numbers of deaths and hospital admissions due to short-term exposure to sulphur dioxide
Time-series epidemiological studies of short-term exposure to sulphur dioxide have shown associations with deaths and respiratory hospital admissions. COMEAP recommended estimates (coefficients from time-series studies) to calculate the numbers of deaths and respiratory hospital admissions due to short-term exposure to sulphur dioxide in 1998 (see Table 1). Read more about Epidemiological studies.
Deaths (all causes)
Respiratory hospital admissions
+ 0.6 % per 50 µg/m3 increase in SO2 24 hour mean
+0.5% per 10 µg/m3 increase in SO2 24 hour mean
Table 1 Estimates of Coefficients to quantify the health effects of short-term exposure to sulphur dioxide (SO2) COMEAP 1998
Since then associations with cardiovascular disease have been reported, read about this in the section on Cardiovascular disease and air pollution
Many epidemiological studies have shown links between the risk of death and long-term average concentrations of sulphur dioxide (for example, Pope et al 2002), It is unclear whether the effect is due to sulphur dioxide itself or to acidic particles produced by reactions involving sulphur dioxide.
There is a positive and statistically significant association for sulphur dioxide and all-cause mortality. COMEAP noted this in the 2009 report, Long-Term Exposure to Air Pollution: Effect on Mortality PDF,1.5 MB Is this a direct effect of sulphur dioxide or an apparent effect due to sulphur dioxide acting as a marker for combustion sources, industrial emissions, especially?
COMEAP did not make any recommendations for quantifying the effects associated with long-term exposure to sulphur dioxide. This may become possible if more evidence accumulates.
This gas is a respiratory irritant. Short-term exposures can exacerbate existing asthma (which formed the basis for the Expert Panel on Air Quality Standards (EPAQS) Air Quality Standard for sulphur dioxide in 1995), while longer-term exposures are associated with the development of chronic bronchitis and /or mucus hypersecretion.
Since the review by EPAQS there have been a number of epidemiological studies confirming clear associations between sulphur dioxide and specific health outcomes, both respiratory and cardiovascular.
The 2006 COMEAP report on cardiovascular disease and air pollution summarised the epidemiological studies published up to that date, showing clear associations between short-term exposures (24 hour) and
• cardiovascular deaths,
• cardiovascular hospital admissions
• ischaemic heart disease hospital admissions.
There is no clear association between short-term exposure to sulphur dioxide and admissions for heart failure or cerebrovascular disease. The evidence is less strong for effects from long-term exposures.
Extract from COMEAP's Review of the UK Air Quality Index (2011)