A-Z site index | Search | Links | Contact DH | Help

Introduction
Sulphur dioxide
Nitrogen dioxide
Ozone
General points
Numerical index
Conclusions
References
Annex: Proposed sub-divisions for numerical index

(This paper was circulated to COMEAP and commented on in writing. It was not discussed at the COMEAP meeting on 16^th June. The amended version of the description of the health effects can be found in a separate document: COMEAP Comments on the DETR Air Pollution Information Service - numerical index and EC alert thresholds )

Introduction

1. The first EC Air Quality Daughter Directive (agreed June 1998) contains a requirement to provide information on health effects to the public once levels of sulphur dioxide or nitrogen dioxide exceed a defined 'alert threshold'. This requirement needs to be implemented by January 2001. As Members are aware, DETR already has an air quality information service but the breakpoints of, for example, the change from the moderate to the high band do not match the relevant EC alert thresholds. Therefore, there is a need to consider how to implement the EC requirement in the UK.

2. COMEAP put a great deal of effort into defining the breakpoints in the past and the 1997 COMEAP Statement explaining how this was done is on the COMEAP website. This was based on health evidence, mainly from chamber studies. This evidence has not changed significantly since. Although it would be an option to amend the breakpoints to match the EC thresholds, this would result in a loss of continuity over time which would not be justified by a change in the health evidence. It has therefore been proposed that information about exceedances of EC alert thresholds is provided separately, for example as an extra page after the usual air quality information on CEEFAX/TELETEXT.

3. The EC Directive requires that, when the threshold is exceeded, information is provided about the sensitive groups affected and any action that they can take. Although this information is provided in general terms as part of the air quality information service, the exceedance of an EC alert threshold will be pollutant specific. It is therefore proposed that a pollutant specific description of the health effects should be provided when the alert threshold is exceeded. The Committee is asked to consider the proposed wording given below. The wording needs to be short and simple in order to fit onto a CEEFAX/TELETEXT page.

Sulphur dioxide

4. The EC Alert Threshold for sulphur dioxide is 500 µg/m³ (187 ppb) as an hourly average measured over 3 consecutive hours. NETCEN are undertaking an analysis of past UK data to see what level of 15 minute means are likely to occur in a situation where the Alert threshold is exceeded. This level is likely to be in the high band.

5. The COMEAP Statement on Banding of Air Quality includes the following:

'200 - 400 ppb (15 minute average): "high" levels of air pollution. The World Health Organisation has suggested that exposure to 400 ppb sulphur dioxide may lead to significant narrowing of the airways in those suffering from asthma. For most people the effects expected would not be large though some individuals may be clinically affected. The effects would be reversed by use of the "reliever inhalers" used by those suffering from asthma. Exposure to such concentrations may add to the effects of exposure to other pollutants and allergens and thus asthmatics should be warned that they may need to increase their medication.'

6. The relevant studies are listed in Annex 6B of the 1992 MAAPE report on sulphur dioxide and discussed in paragraphs 6.18 to 6.21 and 6.50 to 6.51 of that report. These paragraphs conclude that there are clearly effects on asthmatics at 400 ppb but that a small number of asthmatic patients may develop symptoms when exercising and breathing concentrations around 200 ppb.

7. The revision of the WHO Air Quality Guidelines meeting in October 1996 and the COMEAP Update Report paper on chamber studies (1992-1996) circulated in June 1998 did not find any evidence to alter these conclusions.

8. The following wording is therefore suggested to accompany the announcement of an exceedance of the EC Alert Threshold for sulphur dioxide:

'Narrowing of the airways may occur in some asthmatics. Use of their 'reliever' inhaler should lessen this effect.'

Nitrogen dioxide

9. The EC alert threshold is 400 µg/m³ (210ppb) as an hourly average over 3 consecutive hours. This is in the moderate band.

10. The COMEAP Statement on Banding of Air Quality includes the following:

'150 - 300 ppb (1 hour average): " moderate" levels of air pollution. Studies of volunteers, including those with asthma, exposed to concentrations of up to 300 ppb for one hour do not provide convincing evidence that significant effects on health are likely. Some increase in the response of the lung to substances which produce narrowing of the airways have been recorded on exposure to nitrogen dioxide at these concentrations. Again the studies are inconsistent and the effects are small.'

11. The relevant studies are listed in Annex 6B and 6C and Table 6.2 and presented pictorially in Figures 6.1 and 6.2 of the 1993 MAAPE report on NO₂. This highlights some of the inconsistencies with just a few studies showing marginal effects on airway responsiveness below 300 ppb and several studies finding no effects.

12. WHO in its October 1996 revision of the Air Quality Guidelines suggested that the lowest observed adverse effect level was in the range 200 to 300 ppb. The lower end of the range (200 ppb) is probably derived from Kleinman et al 1983 which found a borderline increase in methacholine reactivity in asthmatic patients after exposure to 200 ppb NO₂ for 2 hours with some exercise. (EPAQS also chose a lowest effect level of 200 ppb.) WHO were also influenced by a metaanalysis by Folinsbee (1992) which suggested airway reactivity was affected in some subjects at just under 200 ppb. (MAAPE did not comment on this paper, it was probably published after the writing of the MAAPE report was complete).

13. The COMEAP Update Report paper on chamber studies (1992-1996) circulated in June 1998 did not find any evidence to alter the MAAPE view. (The paper noted effects on FVC and FEV1 in COPD patients at 300 ppb but no effects on normal subjects or patients with mild asthma; effects on histamine responsiveness in patients with mild asthma at 240 ppb and effects on responsiveness to allergen at 400 ppb).

14. The EC requires a statement about the population groups affected. The evidence described above relates to asthmatics. Although strictly an effect on airway responsiveness in normal subjects cannot be ruled out since this hasn't been tested (see discussion in MAAPE report), it is probably reasonable to regard asthmatics as the affected group. COPD patients have not been as extensively studied.

15. The term 'alert threshold' might suggest that alarming health effects might be expected in the general population including asthmatics. However, the chamber study evidence suggests only small effects. (The epidemiological evidence does suggest effects but this is difficult to disentangle from other pollutants).

16. The following wording is suggested when the alert threshold for nitrogen dioxide is exceeded:

'The airway response to factors which narrow the airways may be slightly increased in some people with lung disease. Use of a 'reliever' inhaler should lessen this effect. Exposure can be reduced by avoiding busy streets.'

Ozone

17. Currently, there is an EC Information threshold at 90 ppb and an EC Alert threshold at 180 ppb. However, a new ozone directive is now under discussion and this contains a proposal to change the EC alert threshold for ozone from 180 ppb to 120 ppb. This is in the high band.

18. The COMEAP Statement on Banding of Air Quality includes the following:

'At concentrations of ozone of less than 90 ppb it is very unlikely that anyone will notice any adverse effects though effects are detectable at a population level. As concentrations rise towards 180 ppb some individuals, particularly those exercising out of doors, may experience eye irritation, coughing and discomfort on breathing deeply. At more than 180 ppb these effects may become more severe. Individuals suffering from asthma and other respiratory disorders associated with a reduction in respiratory reserve, may experience earlier and more marked effects.'

19. The effects of ozone on lung function increase continuously with dose (see Fig 5.1 of the MAAPE report on ozone). However, the WHO revision of the Air Quality Guidelines in October 1996 suggested the following starting points for effects after 1 to 3 hours of exposure to ozone during moderate to heavy exercise:

20. Respiratory symptoms do not necessarily track exactly with lung function changes. Cough can occur at 120ppb for 2 hours with heavy exercise (McDonnell et al 1993) or at 180 ppb for 6.8 hours at rest (Seal et al 1996). The WHO Guidelines quote a range from 150 to 200 ppb for the occurrence of cough (duration/exercise not stated) from EPA (1994).

21. The Secretariat prepared a paper on ozone chamber studies in April 1999 for the COMEAP Update. (This was sent to Professor Tattersfield but was not taken further as it was agreed the Update would concentrate on epidemiology) This paper covered a considerable number of chamber studies published since the last MAAPE report. However, overall there was no indication that any major change to the MAAPE view was needed (meaningful changes in lung function start between 100 and 150 ppb).

22. The EC alert threshold is an hourly average. It should be noted that raised levels of ozone would be expected to last longer than an hour and that ozone effects are influenced by both concentration and duration.

23. There is a marked variation in sensitivity to ozone but asthmatics are not necessarily more sensitive.

24. The following wording is suggested presuming that the ozone alert threshold will be agreed at 120 ppb.

'Some people are more sensitive to ozone than others and may begin to notice an effect on their breathing. Exposure to ozone can be reduced by avoiding exercise outdoors in the afternoon. People with asthma are not necessarily more sensitive but, if affected, can use their 'reliever' inhaler.'

General points

25. The description of the health effects has been based mainly on chamber study evidence. The information service as a whole is aimed at the general population including asthmatics. Epidemiological studies suggest effects at lower doses and it is thought that these effects occur in people who are more seriously ill. This is explained in the DETR leaflet 'Air Pollution - What it means for your health' and CEEFAX/TELETEXT refers people to this leaflet for further information.

Numerical index

26. COMEAP agreed to the general principle of using a numerical index at the October 1999 meeting. This would still be linked to the breakpoints previously agreed but would have arbitary subdivisions within the bands. An annex was attached to COMEAP/99/12 setting out these subdivisions. This allocated a numerical index of 1-3 to the low band, 4-5 to moderate, 6-7 to high and 8-10 to very high. Since pollutant levels almost never reach the very high band, the Secretariat now propose that a numerical index of 10 is allocated to the very high band and the remaining bands are each divided into 3. Details of the subdivisions are in the attached annex.

Conclusions

27. The Committee is asked whether it is content with

(i) the proposed descriptions of the health effects to be provided when the alert thresholds are exceeded;

(ii) the proposed subdivisions for the numerical index.

The Committee's views will be fed into a public consultation paper on the proposed changes to the air quality information service.

Secretariat

June 2000

References

Sulphur dioxide

Department of Health. Advisory Group on the Medical Aspects of Air Pollution Episodes. Second Report. Sulphur Dioxide, Acid Aerosols and Particulates. London: HMSO, 1992.

Nitrogen dioxide

Department of Health. Advisory Group on the Medical Aspects of Air Pollution Episodes. Third Report. Oxides of Nitrogen. London: HMSO, 1993.

Kleinman et al (1983) J. Toxicol. Env. Health 12: 815-826

Folinsbee (1992) Tox. Ind. Health 8: 273-283.

Ozone

Department of Health. Advisory Group on the Medical Aspects of Air Pollution Episodes. First Report. Ozone. London: HMSO, 1991.

Gong et al 1986 Am. Rev. Resp. Dis. 134: 726-733.

Horstman et al 1990 Am. Rev. Resp. Dis. 142: 1158-1163.

McDonnell et al 1993 J. Appl. Physiol. 54: 1345-1352.

Seal et al 1993 Am. Rev. Resp. Dis. 147: 804-810.

Seal et al 1996 Am. J. Resp. Crit. Care Med. 153 (4 Part 2): A303

ANNEX: PROPOSED SUBDIVISIONS FOR NUMERICAL INDEX

Top

copyright: © | last updated 17 July 2002