UK Air Quality Limits

There are a wide range of terms and concepts in national and international initiatives, for example, standards, objectives, target values and limit values. The two which feature within the UK’s air quality strategy are standards and objectives. The Air Quality Standards Regulations 2010 contain Limit Values and Target Values.

The national Air Quality Objectives and Air Quality Standards Reglations limit and target values with which the UK must comply are summarised in the National air quality objectives (PDF 262 KB) of the Air Quality Strategy.

Definitions:

• Air Quality Standards are concentrations recorded over a given time period, which are considered to be acceptable in terms 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 indicate whether air pollution is getting better or worse.
• An exceedance is a period of time (defined for each standard) where the concentration is higher than that set out in the Standard. In order to make useful comparisons between pollutants, (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.
• An objective is the target date on which exceedances of a Standard must not exceed a specified number.
• 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 covering different endpoints or averaging times.
• Target values – are set out in the same way as limit values. They are to be attained where possible by taking all necessary measures not entailing disproportionate costs.