DEPARTMENT FOR
ENVIRONMENT, FOOD AND RURAL AFFAIRS News Release (STATISTICAL
RELEASE 118/08) issued by The Government News Network on 29 April 2008
The air quality
indicator is one of the 68 indicators of the Government's
Sustainable Development Strategy. It measures annual levels of
pollution from particulates (PM10) and ozone (O3), 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:
* Urban background particulate levels averaged 22 microgrammes
per cubic metre (ug m-3) in 2007 compared to 24ug m-3 in 2006.
These levels have fluctuated in the last 5 years, although there
has been an overall decreasing trend since 1993, the first year
for which data were available.
* Roadside particulate levels averaged 29 ug m-3 in 2007 compared
to 32 ug m-3 in 2006. There has been a general downward trend
since monitoring began in 1997, although this decline has slowed
since 2001.
* Rural ozone levels* averaged 67 ug m-3 in 2007 compared to 74
ug m-3 in 2006 and 68 ug m-3 in 1993. There is no clear long term trend.
* Urban background ozone levels averaged 57 ug m-3 in 2007
compared to 61 ug m-3 in 2006 and 44 ug m-3 in 1992. These levels
have shown an overall increasing long term trend since 1992, the
first year for which data were available.
* In urban areas, air pollution in 2007 was recorded as moderate
or higher on 24 days on average per site, compared with 41 days in
2006, and 59 days in 1993. This series has reflected a high degree
of year-on-year variability over time, and this has again been
apparent for 2007.
* In rural areas, air pollution in 2007 was moderate or higher
for 24 days on average per site, compared with 56 days in 2006.
This figure has also varied significantly over time.
* These figures are an update of the provisional figures
published on 24th January 2008. The slight differences between
figures published today and those published in January are due to
the full quality control (ratification) process.
Background
An air quality "headline" indicator was introduced in
1999 in support of the UK Sustainable Development Strategy. When
this strategy was updated in 2005, a new air quality indicator was
included, better reflecting the effects on health of long term
exposure to lower levels of pollution. The indicator is split into
two parts covering; (a) annual exposure to pollutants and (b) the
number of days when levels of pollutants are moderate or higher.
Particulates and ozone
Part (a) of the indicator measures annual exposure to
particulates and ozone (see Figure (a) below). It was introduced
in the light of increasing evidence suggesting that long-term
exposure to even low levels of particulates (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 hot, still, sunny days. There is an upward trend
in urban 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.
Days with moderate or higher air pollution
Part (b) of the indicator measures days of moderate or higher
pollution according to the Air Pollution Information Service
bandings used in air pollution forecasting (see Figure (b) below).
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, particulates 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 particulates
(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 1992.
Tables A and B below show the data underlying Parts (a) and (b)
of the indicator respectively.
Table A: Annual average levels of Ozone and PM10 (ug 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 24 32 61 74
2007 22 29 57 67
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
Not every site in the automatic monitoring network is included.
Sites must also meet certain data capture targets to be used in
the index. For both ozone and PM10, from 1987-97 data capture
should be more than or equal to 50% of the year and from 1998
onwards it should be more than or equal to 75% of the year. For
ozone this applies to both the full year and the summer period
only. .
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 41 56
2007 24 24
Notes to Table B:
.. not available because of insufficient data
Not every site in the automatic monitoring network is included.
Sites must also meet certain data capture targets to be used in
the index. For both ozone and PM10, from 1987-97 data capture
should be more than or equal to 50% of the year, and from 1998
onwards it should be more than or equal to 75% of the year. For
ozone this applies to both the full year and the summer period only.
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
to the indicator in 2006 - Birmingham Tyburn and Wigan Centre
(replacing Birmingham East and Wigan Leigh respectively).
Causes of air pollution in urban sites
Two of the five pollutants, ozone and particulates, caused over
99 per cent of the pollution days, either separately or in
combination with each other (see Figure (c) below). Between 1993
and 2007, the average number of days of pollution at urban sites
caused by particulates, solely or in combination with other
pollutants, fell from an average per site of about 43 days to 12
days per year. Particulates come from numerous man-made and
natural sources, and can be generated in the UK or transported
from abroad. UK emissions of particulates 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
days in 2003.
The average number of pollution days at urban sites caused by
sulphur dioxide, solely or in combination with other pollutants,
was 20 days per site in 1993. In 2007 sulphur dioxide did not
cause any pollution days, either solely or in combinations with
other pollutants.
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 particulates have, as pollution by particulates
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, 2003 and 2006 led to the greatest
number of days of moderate or higher ozone pollution since this
series began in 1987. 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.
These results are shown in Figure (c) and Table C below.
Table C: Average number of days of moderate or higher air
pollution per site caused by the each of the basket of 5 pollutants
Year Ozone Nitrogen Carbon Sulphur Particulates
dioxide monoxide dioxide
1993 5 0 0 20 43
1994 13 0 0 13 27
1995 24 1 0 12 28
1996 17 0 0 6 30
1997 16 1 0 4 23
1998 10 0 0 3 13
1999 25 0 0 1 9
2000 13 0 0 1 7
2001 17 0 0 0 8
2002 14 0 0 0 6
2003 36 0 0 0 17
2004 18 0 0 0 4
2005 16 1 0 0 6
2006 33 0 0 0 10
2007 12 1 0 0 12
Notes to Table C:
Not every site in the automatic monitoring network is included.
Sites must also meet certain data capture targets to be used in
the index. For both ozone and PM10, from 1993-97 data capture
should be more than or equal to 50% of the year, and from 1998
onwards it should be more than or equal to 75% of the year. For
ozone this applies to both the full year and the summer period
only. 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.
Changes to the UK automatic monitoring network and the indicator calculation
The proposed EU Directive on Ambient Air Quality and Cleaner Air
for Europe is expected to come into force in May/June 2008, and
provides a new regulatory framework for very small particles
(PM2.5). This Directive requires measurements of the
concentrations of these particles as well as measurements of
larger particles (PM10), and also requires that measurements are
comparable in all EU member states. In order to fulfil these
requirements some changes are needed to the UK automatic
monitoring network. These changes include the number of sites
monitored, the pollutants and locations to be monitored, and the
monitoring techniques to be used.
The changes will be phased in over a period which began on 2nd
October 2007 and will be completed by the end of 2008. New
equipment is being introduced at some monitoring sites to enable
reference method equivalent measurements of PM10 and PM2.5 to be
made. The composition of sites in the monitoring network has also
been reviewed with more emphasis being placed on roadside
locations. This will change the ratio from the current 1 roadside
site for every 4 or 5 urban background sites to 1 roadside site
for every 2 urban background sites. The number of sites monitoring
carbon monoxide (CO) and sulphur dioxide (SO2) has been greatly
reduced. The number of sites measuring nitrogen dioxide (NO2) and
ozone (O3) has been increased, and around 75 new sites will be
introduced to measure PM2.5. Since the first of these changes was
introduced in October 2007, only 3 months of 2007 results have
been affected but it is anticipated that the 2008 results will be
affected to a greater degree.
Due to these changes to the composition of the automatic
monitoring network, changes will also have to be made to the
composition of the sites included in the calculation for Part (b)
of the indicator. Currently, not all sites in the automatic
monitoring network are included in the calculation for Part (b) of
the indicator. This is because the composition of sites used for
this calculation is based on a sub-set of 67 sites that was
identified in 2001, to improve year-to-year consistency in the
indicator calculation. Therefore, since 2001, only data from these
sites have been considered for inclusion. However, following the
changes to the automatic monitoring network, many of the original
67 sites will no longer measure CO or SO2, and many of the new
sites introduced to monitor PM2.5, NO2 and O3 will not be within
this original sub-set of 67 sites. It is therefore no longer
appropriate to continue to monitor only the 67 sites identified in
2001, and a new method of determining the composition of sites for
the indicator calculation will therefore be used from 2008
onwards. Various options for this are now being considered. One
approach might be to base the indicator on all sites (with data
capture over 75%) in the automatic monitoring network, rather than
basing it on a sub-set of sites. This will ensure that the
current, and future, changes to the automatic monitoring network
are fully represented in the indicator calculation and will also
align the indicator more closely with EU reporting.
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. The banding system used in Part (b) of
the indicator is that of the Air Pollution Information Service.
2. More detailed data and information are published on the UK Air
Quality Archive.
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 or
can be ordered by calling the Defra free publications service on
08459 556000.
4. Further details and data relating to UK air quality is
available on Defra's e-Digest of Environmental Statistics: http://www.defra.gov.uk/environment/statistics/airqual/index.htm
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.
* Measured as the daily maximum 8-hour running mean
Department for Environment, Food and Rural Affairs
Nobel
House, 17 Smith Square, London, SW1P 3JR