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Air Quality Standards and Objectives

Standards for air pollution are concentrations over a given time period that are considered to be acceptable in the light of what is scientifically known about the effects of each pollutant on health and on the environment. They can also be used as a benchmark to see if air pollution is getting better or worse.

An exceedence of a standard is a period of time (which is defined in each standard) where the concentration is higher than that set down by the standard. In order to make useful comparisons between pollutants, for which the standards may be expressed in terms of different averaging times, the number of days on which an exceedence has been recorded is often reported.

An objective is the target date on which exceedences of a standard must not exceed a specified number.

The objectives adopted in the UK are defined in the latest Air Quality Strategy for England, Scotland, Wales and Northern Ireland, published on 17th July 2007. Those which are limit values required by EU Daughter Directives on Air Quality have been transposed into UK law through the Air Quality Standards Regulations 2007 which came into force on 15th February 2007.

A summary of the current UK Air Quality Objectives is provided here.

Summary of objectives of the National Air Quality Strategy

Pollutant Air Quality Objective To be achieved by
Concentration Measured as
Benzene      
All authorities 16.25 µg m-3 Running Annual Mean 31 December 2003
England and Wales Only 5.00 µg m-3 Annual mean 31 December 2010
1,3-Butadiene 2.25 µg m-3 Running Annual Mean 31 December 2003
Carbon Monoxide      
England, Wales and N. Ireland 10.0 mg m-3 Maximum daily running 8 Hour Mean 31 December 2003
Lead 0.5 µg m-3 Annual mean 31 December 2004
  0.25 µg m-3 Annual mean 31 December 2008
Nitrogen dioxide 200 µg m-3 not to be exceeded more than 18 times per year 1 Hour Mean 31 December 2005
  40 µg m-3 Annual mean 31 December 2005
Particles (PM10) (gravimetric)      
All authorities 50 µg m-3, not to be exceeded more than 35 times per year Daily Mean 31 December 2004
40 µg m-3 Annual mean 31 December 2004
Particles (PM2.5) (gravimetric) * 25 µg m-3 (target) Annual mean 2020
All authorities 15% cut in urban background exposure Annual mean 2010 - 2020
Sulphur Dioxide 350 µg m-3, not to be exceeded more than 24 times per year 1 Hour Mean 31 December 2004
  125 µg m-3, not to be exceeded more than 3 times per year 24 Hour Mean 31 December 2004
  266 µg m-3, not to be exceeded more than 35 times per year 15 Minute Mean 31 December 2005
PAH * 0.25 ng m-3 Annual mean 31 December 2010
Ozone * 100 µg m-3 not to be exceeded more than 10 times per year 8 hourly running or hourly mean* 31 December 2005

* not included in regulations
      Shaded data shows new objectives



UK Air Quality Objectives for protection of vegetation and ecosystems - July 2007

Pollutant Air Quality Objective To be achieved by
Concentration Measured as
Nitrogen dioxide (for protection of vegetation & ecosystems) * 30 µg m-3 Annual mean 31 December 2000
Sulphur Dioxide (for protection of vegetation & ecosystems) * 20 µg m-3
20 µg m-3
Annual mean
Winter Average (Oct - Mar)
31 December 2000
Ozone * 18000 µg m-3.h AOT40+, calculated from 1h values May-July. Mean of 5 years, starting 2010 01 January 2010

*not included in regulations
+ AOT 40 is the sum of the differences between hourly concentrations greater than 80 µg m-3 (=40ppb) and 80 µg m-3, over a given period using only the 1-hour averages measured between 0800 and 2000.
      Shaded data shows new objectives