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Air quality is measured by comparing against a range of health-effects based standards.

This page gives information about what this means.

Air Quality Standards and Objectives

A set of air quality standards and objectives has been developed for several pollutants of concern for human health.  Standards are concentrations of pollutants that are considered safe for humans and the environment. Objectives are derived from the standards and are a compromise between what is desirable purely on health grounds and what is practical in terms of feasibility and costs. Each objective has a date by when it must be achieved.

The objectives adopted in Scotland for the purpose of Local Air Quality Management are set out in the Air Quality (Scotland) Regulations 2000, the Air Quality (Scotland) Amendment Regulations 2002 and the Air Quality (Scotland) Amendment Regulations 2016. Similar targets are set at EU level, where there are called limit or target values. These are set out in the European 2008 Ambient Air Quality Directive (2008/50/EC) and transposed into Scottish legislation by the Air Quality Standards (Scotland) Regulations 2010. It is the responsibility of EU Member States to achieve the limit and target values.

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

Summary of objectives of the National Air Quality Strategy

Pollutant Air Quality Objective To be achieved by
Concentration Measured as
Benzene      
All UK authorities 16.25 µg m-3 Running annual mean 31 December 2003
Authorities in Scotland and N. Ireland 3.25 µg m-3 Running annual mean 31 December 2010
1,3-Butadiene 2.25 µg m-3 Running annual mean 31 December 2003
Carbon Monoxide      
Authorities in Scotland Only 10.0 mg m-3 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 a 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 a year 24 Hour mean 31 December 2004
  40 µg m-3 Annual mean 31 December 2004
Scotland Only 50 µg m-3, not to be exceeded more than 7 times a year 24 Hour mean 31 December 2010
  18 µg m-3 Annual mean 31 December 2010
Particles (PM2.5) (gravimetric) * 25 µg m-3 (target) Annual mean 2020
All UK authorities 15% cut in urban background exposure Annual mean 2010 - 2020
Authorities in Scotland Only 10 µg m-3 (limit) Annual mean 2020
Sulphur dioxide 350 µg m-3, not to be exceeded more than 24 times a year 1-hour mean 31 December 2004
  125 µg m-3, not to be exceeded more than 3 times a year 24-hour mean 31 December 2004
  266 µg m-3, not to be exceeded more than 35 times a 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 a year 8 hourly running or hourly mean* 31 December 2005

* not currently assessed by Scottish local authorities.

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

Pollutant Concentration Air Quality Objective To be achieved by
Oxides of Nitrogen (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 currently assessed by Scottish local authorities.
+ 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.