Air-Quality Standards

Pollutant Standard	Standard
	Concentration^a	Measured as Benzene
Benzene	5ppb (16.25µg/m^3)	running annual mean
1,3-Butadiene	1ppb (2.25µg/m^3)	running annual mean
Carbon monoxide	10ppm (11.6mg/m^3)	running 8 hour mean
Lead	0.25µg/m^3	annual mean
Nitrogen dioxide	150ppb (287µg/m^3)	1 hour mean
Ozone	50ppb (100µg/m3)	running 8 hour mean
Particles (PM10)	50µg/m^3	running 24 hour mean
Sulphur dioxide	100ppb (266µg/m^3)	15 minute mean

^aConversions of ppb and ppm to µg/m³ and mg/m³ at 20ºC and 1013mb. ppb = parts per billion; ppm = parts per million; µg/m³ = microgrammes per cubic metre; mg/m³ = milligrammes per cubic metre

Source: The Air Quality Strategy for England, Scotland, Wales and Northern Ireland. Department for the Environment, Food and Rural Affairs in partnership with the Scottish Executive, The National Assembly for Wales and the Department of the Environment for Northern Ireland, 2000.