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STATISTICAL RELEASE

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Air quality indicator for sustainable development 2006 (provisional)

The air quality indicator is one of the 68 indicators of the Government’s Sustainable Development Strategy. It presents trends for annual levels of particulate and ozone pollution, the two pollutants thought to have the greatest health impacts, as well as the number of days on which levels of any one of a basket of five pollutants were ‘moderate or higher’.

The main results are:

• Annual average urban background particulate (PM₁₀) levels were 24 microgrammes per cubic metre (µg m^-3) in 2006 compared to 22 in 2005. These levels have increased slightly in each of the last two years, although there has been an overall decreasing trend since 1993, the first year for which data was available.
• Rural ozone levels (measured as the daily maximum 8-hour running mean) averaged 74 µg m^-3 in 2006 compared to 70 µg m^-3 in 2005 and 68 µg m^-3 in 1993. There is no clear long term trend.
• Urban background ozone levels were 61 µg m^-3 in 2006 compared to 57 µg m^-3 in 2005. These levels have shown an overall increasing long term trend since 1993.
• In urban areas in 2006, air pollution was recorded as moderate or higher on 41 days on average per site, compared with 22 days in 2005,  and 59 days in 1993, reflecting a high degree of variability.
• In rural areas, air pollution in 2006 was moderate or higher for 57 days on average per site, compared with 40 in 2005.  This figure has varied significantly over time, although there appears to be a gradually increasing long term trend.

Figure A

Figure B

Background

In 1999, an air quality “headline” indicator was introduced in support of the UK Sustainable Development Strategy . When this strategy was updated in 2005 a new air quality indicator was added, better reflecting the effects on health of long term exposure to lower levels of pollution.

Part (a) of the indicator shows trends for annual exposure to particles and ozone. It has been introduced because there is increasing evidence that suggests long-term exposure to even low levels of particulate (PM₁₀) may have a significant effect on public health. The annual mean values for particulates are a useful measure of overall exposure to particulates at all concentrations. The annual average measures of PM₁₀ have been included to reflect this.

The impact of long term exposure to low levels of ozone is currently less clear but if there is no lower limit on the levels which have a health impact then the parameter used in the indicator gives the best representation of the overall annual impact of the short term effects of ozone pollution. The production of ozone is strongly influenced by the weather, more being created on sunny days. There is a very slight upward trend in background ozone levels in the UK, in common with rising hemispheric ozone levels, but this is not particularly evident in the rural ozone index. There is a more marked increase in urban areas, due to the reduction in urban emissions of nitrogen oxides, which tend to destroy ozone close to their emission source.

Part (b) of the indicator formed the old ‘headline’ indicator and measures days of moderate or higher pollution according to the Air Pollution Information Service bandings used in weather forecasting. At the moderate level the effects of pollution may start to be noticeable to sensitive people. There is no clear trend in the number of either urban or rural pollution days due to the effects of variability in weather patterns from year to year.

The bandings are based on 5 pollutants consisting of carbon monoxide, nitrogen dioxide, ozone, fine particles and sulphur dioxide. These are recognised as the most important for causing short term health effects. The main causes of days of moderate or higher air pollution at urban sites are ozone and fine particles (PM₁₀). Sulphur dioxide also used to make a significant contribution but has now fallen to relatively very low levels. Carbon monoxide and nitrogen dioxide, have very rarely reached moderate or higher levels since the urban index began in 1993.

Three of the five pollutants, ozone, fine particles and sulphur dioxide provide 99 per cent of the pollution days, either separately or in combination with each other. These are shown in Figure (c). Between 1993 and 2006, the average number of days of pollution at urban sites caused by fine particles, solely or in combination with other pollutants, fell from an average per site of about 43 days to 10 days per year. Particles come from numerous man-made and natural sources, and can be generated in the UK or transported from abroad. UK emissions of particles have been reduced substantially in recent years, but the number of pollution days can still fluctuate from year to year due to variations in weather conditions, as demonstrated by the unusually high figure of 17 in 2003.

The average number of polluted days caused by sulphur dioxide, solely or in combination, fell from an average of 20 days per site in 1993 to 0.1 days per site in 2006. 

Figure C

 

Ozone causes the great majority of pollution days in rural areas. Since 1999 it has also caused more days of poor air quality in urban areas than particles have, as pollution by particles has declined. The number of days caused by ozone pollution has fluctuated in both rural and urban areas, with no clear overall trend. The hot summers in 1999 and 2003 led to the greatest number of days of moderate or higher ozone pollution since this series began in 1987. The high figures in 2006 were also associated with a hot summer. A proportion of the ozone experienced in the UK originates from releases of pollution that are blown over from mainland Europe.

The series can be volatile from one year to the next, reflecting the variability in levels of ozone, more of which is produced in hot, sunny weather, as was the case during 2003 and 2006.

Table A: Annual levels of Ozone and PM₁₀ (provisional) (μg m^-3)

	PM10		Ozone
Year	Urban Background	Roadside	Urban Background	Rural
1987	..	..	..	60
1988	..	..	..	67
1989	..	..	..	70
1990	..	..	..	72
1991	..	..	..	68
1992	..	..	44	71
1993	36	..	42	68
1994	32	..	48	72
1995	31	..	52	72
1996	31	..	48	68
1997	30	37	47	68
1998	26	33	50	69
1999	24	32	57	73
2000	23	31	53	68
2001	24	31	52	67
2002	23	29	54	68
2003	25	31	60	74
2004	22	27	57	73
2005	22	29	57	70
2006 (p)	24	35	61	74

Notes to Table A

• PM₁₀: annual mean: average across all monitoring sites.
• Ozone: annual mean of the daily maximum 8 hour running mean: average across all monitoring sites
• ..  not available because of insufficient data
• Sites must meet certain data capture targets to be used in the index. Therefore not every site in the automatic monitoring network is included. For both ozone and PM₁₀ from 1987-97 data capture should be more than or equal to 50%, from 1998 onwards it should be more than or equal to 75%. For ozone this applies to both the annual and summer periods.

Table B:  Average number of days of moderate or higher air pollution per site

Year	Urban sites	Rural sites
1987	..	21
1988	..	31
1989	..	47
1990	..	50
1991	..	48
1992	..	44
1993	59	33
1994	47	44
1995	50	44
1996	48	41
1997	40	42
1998	24	29
1999	33	48
2000	21	27
2001	25	34
2002	20	32
2003	50	64
2004	23	44
2005	22	40
2006 (p)	41	57

Notes to Table B

• ..  not available because of insufficient data
• Sites must monitor a range of pollutants and meet certain data capture targets to be used in the index. Therefore not every site in the automatic monitoring network is included. Data capture was slightly below the recommended 75% minimum for sulphur dioxide for Manchester Piccadilly in 1998 and for Port Talbot in 1999; and for ozone for Narberth in 2000.  However, Defra believe that greater consistency in trends is achieved by including the data for the above sites than by excluding them.  Manchester Piccadilly was excluded in 2001, and Cardiff Centre in 1994, because stone cutting adjacent to the sites caused unrepresentative results. Narberth rural site was excluded for giving incorrect measurements during 2004
• 2 urban sites were added in 2006 Birmingham Tyburn and Wigan Centre.

 

Notes to editors

1. The air quality indicator is one of the 68 indicators of the Government’s Sustainable Development Strategy published in March 2005, and includes the former air quality headline indicator of sustainable development www.sustainable-development.gov.uk. The banding system used in Part b is that of the Air Pollution Information Service (www.airquality.co.uk/archive/standards.php#band).

2. More detailed data and information are published on the Air Quality Archive at www.airquality.co.uk/archive/index.php.

3. Information about the health effects of air pollution can be found in the leaflet 'Air Pollution - what it means for your health'. This leaflet is available on the Defra website at www.defra.gov.uk/environment/airquality/publications/airpoll/index.htm or can be ordered by calling the Defra free publications service on 08459 556000.

A National Statistics publication

National Statistics are produced to high professional standards set out in the National Statistics Code of Practice. They undergo regular quality assurance reviews to ensure they meet customer needs.

End

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Page published: 23 January 2007

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