Air Quality targets 

Air quality is devolved subject and Scotland can sets its own policies and regulations (subject to retained EU law frameworks).The air quality regulations in Scotland flows from EU 2008 directives. The 2008 ambient air quality dirrecitve (2008/50/EC) sets legally binding limits for concentrations in ambient (outdoor) air of major air pollutatns that are known to have a significant impact on human health including particulate matter (PM10 and PM2.5) and nitrofen dioxide (NO2). Following the UK’s exit from the EU, under retained EU law, the UK is required to continue meeting limit and target values for a range of air pollutants covered by the directive.

The 2008 directive was made law in Scotland through the Air Quality Standards (Scotland) Regulations 2010. The air quality regulations first came up for Scotland in 2000 but later due to EU 2008 directive the comprehensive set of regulations was enforced through the 2010 regulations. It has also been subsequently amended in 2016. 

Part 2 - Assessment of ambient air quality

The assessment of ambient air quality contained in Part 2 extensively covers all major gases under three chapters, the gases include - Sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter, lead, benzene, carbon monoxide, ozone, arsenic, cadmium, nickel, mercury, benzo(a)pyrene and other polycyclic aromatic hydrocarbons. The regulations also contain provisions under Section 24 for Air Quality Plans in case the levels of mentioned gases exceeds the threshold mentioned in the regulatory schedules. 

In the UK most air pollution n the UK most air pollution information services use the index and banding system approved by the Committee on Medical Effects of Air Pollution Episodes (COMEAP). The system uses 1-10 index divided into four bands to provide more detail about air pollution levels in a simple way, similar to the sun index or pollen index. 
1-3 (Low)
4-6 (Moderate)
7-9 (High)
10 (Very High)
The overall air pollution index for a site or region is calculated from the highest concentration of five pollutants: Nitrogen Dioxide, Sulphur Dioxide, Ozone, Particles PM2.5 and Particles < 10µm (PM10).

Local Air Quality Management (LAQM) regime

The LAQM regime requires every local authority to review air quality in their area. If they find that the limit values for pollutants have been exceeded or will be exceeded they are required to designate air quality management areas (AQMA). The Scottish Government local air quality management policy guidance sets out the legal duties with which local authorities must comply and provides guidance on air quality action planning. This particular regime flows from LAQM duties under Part IV of the Environment Act 1995.  The said act also mandates local authorities to give regard to this guidance issued by the Scottish Ministers under section 88(1) of the 1995 act. Section 12 of this guidance on air quality and land use planning, in particular, should be read together with NPF4.