Air quality standards and objectives

Ambient (outdoor) air quality in Northern Ireland is covered by both UK and European Union (EU) law. This legislation seeks to protect the quality of the air we breathe by setting a range of air quality criteria which must be met.

Various different words are used to describe these criteria: for example, “standards”, “objectives”, “target values” and “limit values”. This page explains what these words mean. This information is based on that provided on UK-AIR’s ‘UK and EU Air Quality Limits’ web page at https://uk-air.defra.gov.uk/air-pollution/uk-eu-limits .

The UK Air Quality Strategy uses the terms “standards” and “objectives”:

A “standard” for air quality is usually a specified concentration of a particular pollutant, measured or averaged over a given time, considered to be the maximum acceptable in the light of what is scientifically known about the effects of the pollutant on health and on the environment.

The standards for different pollutants are based on different averaging periods. Some pollutants have more than one standard, based on more than one averaging period: for example, nitrogen dioxide has a short-term standard based on the hourly mean, and a long-term standard based on the annual mean.

An “objective” includes the target date by which exceedances of a standard must not exceed a specified number.

An “exceedance” of a standard is a period of time (which is defined in each standard) where the concentration is higher than that set out in 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 exceedance has been recorded is often reported. Standards and objectives can also be used as a benchmark to see if air pollution is getting better or worse.

EU legislation – the EU Ambient Air Quality Directive and fourth Daughter Directive – talks about “Limit Values” and “Target Values”:

“Limit values” are legally binding EU parameters that must not be exceeded. Limit values are set for individual pollutants and are made up of a concentration value, an averaging time over which it is to be measured, the number of exceedances allowed per year (if any), and a date by which it must be achieved. Some pollutants have more than one limit value, for example covering different averaging times.

“Target values” are used in some EU Directives and are set out in the same way as limit values. However, where limit values are mandatory, target values are to be attained where possible by taking all necessary measures not entailing disproportionate costs.

At the time of writing (2019), the UK is preparing to leave the European Union.  DAERA has a webpage dedicated to supplying the public with information on this process, which you can find at https://www.daera-ni.gov.uk/brexit.

The objectives adopted in the UK are defined in the Air Quality Strategy for England, Scotland, Wales and Northern Ireland published on 17th July 2007. Those which are also limit values required by the EU Air Quality Directive (2008) have been transposed into UK law through the Air Quality Standards Regulations 2010 which came into force on 11th June 2010. The national Air Quality Objectives and EU limit and target values with which the UK must comply are summarised in the national air quality objectives of the Air Quality Strategy.

A summary of the current UK Air Quality Objectives is provided below. (See also https://uk-air.defra.gov.uk/assets/documents/Air_Quality_Objectives_Update.pdf).

Summary of objectives of the Air Quality Strategy

Pollutant Concentration Measured as To be achieved by
Benzene      
All authorities 16.25 µg m-3 Running annual mean 31 December 2003
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      
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 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
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 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 included in regulations at present

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

Pollutant Concentration Measured as To be achieved by
Nitrogen dioxide (for protection of vegetation & ecosystems) * 30 µg m-3 Annual mean 31 December 2000
Sulphur dioxide (for protection of vegetation & ecosystems) * 30 µg m-3
30 µg m-3
Annual mean
Winter Average (Oct - Mar)
31 December 2000
Ozone * 18 µg m-3 AOT40 +, calculated from 1h values May-July. Mean of 5 years, starting 2010 01 January 2010

* not included in regulations at present

+ 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.

Other air quality standards relevant to human health

Pollutant EU limit value or target value
Concentration Measured as
Arsenic 6 ng m-3 total content in the PM10 fraction average over a calendar year
Benzo(a)pyrene 1 ng m-3 total content in the PM10 fraction average over a calendar year
Cadmium 5 ng-3 total content in the PM10 fraction average over a calendar year
Nickel 20 ng m-3 total content in the PM10 fraction average over a calendar year
Ozone 120 µg m-3 not to be exceeded on more than 25 days a year averaged over three years
(WHO guideline 100 µg m-3)
maximum daily running 8-hour mean
Particles (PM2.5)
(gravimetric)
25 µg m-3
(WHO guideline 10 µg m-3)
annual mean