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AIR QUALITY INDICATOR FOR SUSTAINABLE DEVELOPMENT 2005

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The air quality indicator is one of the 68 indicators of the government's new Sustainable Development Strategy. It ...
The air quality indicator is one of the 68 indicators of the government's new 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'.

Annual average urban background particulate (PM 10) levels remained unchanged at 22 microgrammes per cubic metre (ìg m-3) from 2004 to 2005, generally showing a decreasing trend from 36 ìg m-3 in 1993.

Rural ozone levels (measured as the daily maximum 8-hour running mean) averaged 70 ìg m-3 in 2005 compared to 73 ìg m-3 in 2004 and 68 ìg m-3 in 1993. There is no clear long term trend.

Urban background ozone levels were 57 ìg m-3 in 2005, the same as in 2004 and have generally increased from 42 ìg m-3 since 1993.

In urban areas in 2005, air pollution was recorded as moderate or higher on 22 days on average per site, compared with 23 days in 2004, 50 days in 2003, and 59 days in 1993, reflecting a general decline in urban pollution.

In rural areas, air pollution in 2005 was moderate or higher for 40 days on average per site, compared with 44 in 2004, and 64 in 2003. The number of days has fluctuated between 21 days in 1987 and the 2003 figure of 64 days, showing little overall trend.

The figures are available here.

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. This is the first 'final figures' release for the air quality indicator in its new form, following its original publication in June 2005, and the publication of provisional 2005 figures in January 2006.

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 (PM 10) 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 PM 10 have been included to reflect this. Annual average particulate levels have been decreasing, although the trend may be levelling off.

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 new indicator gives the best representation of the total 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. The number of pollution days in urban areas has decreased, while there has been no clear trend in rural pollution days.

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 (PM 10). 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.

As figure (c) shows, between 1993 and 2005, 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 6 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 per site of 20 days in 1993 to an average of one-tenth of a day per site in 2005.

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 pollution days caused by ozone has fluctuated in both rural and urban areas, with no clear overall trend. The hot summer in 2003 led to the greatest number of days of moderate or higher ozone pollution since this series began in 1987. The high in 1999 was 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, This reflects the variability in levels of ozone, more of which is produced in hot, sunny weather, as was the case during 2003.

Figure C: Causes of air pollution at urban sites

Note: For the purposes of this chart, where a day is caused by more than one pollutant it is counted for each pollutant, ie there is double counting. Source: netcen, Defra.

Table A: Annual levels of Ozone and PM10 (ìg 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 (22)

29 (31)

57 (56)

70 (69)

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 PM 10 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.

In May 2005 a new set of conversion factors between the measurements and the concentrations were applied and statistics were recalculated creating minor differences in decimal places from previous years with the 2003 rural ozone figure rounding to 74 instead of 75.

Figures in brackets show provisional figures published in January 2006 before ratification of data.

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 (22)

40 (41)

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

10 urban and 3 rural sites were added in 2005

Figures in brackets show provisional figures published in January 2006 before ratification of data.

Notes

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).

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

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/airpoll/index.htm or can be ordered by calling the Defra free publications service on 08459 556000.

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