The Air Quality Standards (Wales) Regulations 2010

Regulations 13, 15, 20(1), (2), (4) and (5), 21(5), 23(1) and 24(2)

SCHEDULE 1 Limit values

Sulphur dioxide

Averaging period	Limit value
One hour	350 μg/m3, not to be exceeded more than 24 times a calendar year
One day	125 μg/m3, not to be exceeded more than 3 times a calendar year

Nitrogen dioxide

Averaging period	Limit value
One hour	200 μg/m3, not to be exceeded more than 18 times a calendar year
Calendar year	40 μg/m3

Benzene

Averaging period	Limit value
Calendar year	5 μg/m3

Carbon monoxide

Averaging period	Limit value
Maximum daily eight hour mean(1)	10 mg/m3

Lead

Averaging period	Limit value
Calendar year	0.5 μg/m3

PM₁₀

Averaging period	Limit value
One day	50 μg/m3, not to be exceeded more than 35 times a calendar year
Calendar year	40 μg/m3

PM_2·5

Averaging period	Limit value	Margin of tolerance	Date by which limit value is to be met
Calendar year	25 μg/m3	20% on 11 June 2008, decreasing on the next 1 January and every 12 months thereafter by equal annual percentages to reach 0% by 1 January 2015	1 January 2015

(1)

The maximum daily eight hour mean concentration of carbon monoxide must be selected by examining eight hour running averages, calculated from hourly data and updated each hour. Each eight hour average so calculated must be assigned to the day on which it ends, that is, the first calculation period for any one day will be from 17:00 on the previous day to 01:00 on that day, and the last calculation period for any one day will be the period from 16:00 to 24:00 on that day.