Standards and objectives

Ambient (outdoor) air quality in Northern Ireland is covered by the Air Quality Standards Regulations (Northern Ireland) (2010) and their January 2017 amendment, and also the Air Quality Strategy (2007). These Regulations and the Air Quality Strategy seek 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.

The Air Quality Standards Regulations (Northern Ireland) (2010)

The UK Air Quality Standards Regulations set "Limit Values" and "Target Values":

“Limit values” are legally binding 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 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.

The Air Quality: Provisional Common Framework

The Air Quality: Provisional Common Framework can be found here: https://www.gov.uk/government/publications/air-quality-provisional-common-framework. This command paper sets out how the UK government and devolved governments (including Northern Ireland) propose to work together on policies that aim to reduce harmful emissions and concentrations of air pollutants that can damage human health and the environment, now that we have left the European Union. The provisional common framework has received ministerial approval from all four governments.

The UK Air Quality Strategy (2007)

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.

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. Some of these have subsequently become part of Northern Ireland’s law, via the Air Quality Standards Regulations (Northern Ireland) (2010) which came into force on 11th June 2010. The national Air Quality Objectives and limit and target values with which the UK must comply are summarised in the national air quality objectives of the Air Quality Strategy.

(Note: an updated Air Quality Strategy was published April 2023, replacing the 2007 version in England only. The 2007 Air Quality Strategy remains in force in Northern Ireland until the forthcoming Clean Air Strategy for Northern Ireland is published.)

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

 

* not included in regulations at present

* 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.