The Air Quality Standards Regulations 2007

PART 1 Assessment thresholds for Group A pollutants

Benzene

	Annual average
Upper assessment threshold	70% of limit value (3.5 μg/m³)
Lower assessment threshold	40% of limit value (2 μg/m³)

Carbon monoxide

	Eight-hour average
Upper assessment threshold	70% of limit value (7 mg/m³)
Lower assessment threshold	50% of limit value (5 mg/m³)

Lead

	Annual average
Upper assessment threshold	70% of limit value (0.35 μg/m³)
Lower assessment threshold	50% of limit value (0.25 μg/m³)

Nitrogen dioxide (NO2) and oxides of nitrogen (NOx)

	Hourly limit value for the protection of human health (NO2)	Annual limit value for the protection of human health (NO2)	Annual limit value for the protection of vegetation (NOx)
Upper assessment threshold	70% of limit value (140 μg/m³), not to be exceeded more than 18 times in any calendar year	80% of limit value (32 μg/m³)	80% of limit value (24 μg/m³)
Lower assessment threshold	50% of limit value (100 μg/m³), not to be exceeded more than 18 times in any calendar year	65% of limit value (26 μg/m³)	65% of limit value (19.5 μg/m³)

PM₁₀

	24-hour average	Annual average
Upper assessment threshold	60% of limit value (30 μg/m³), not to be exceeded more than 7 times in any calendar year	70% of limit value (14 μg/m³)
Lower assessment threshold	40% of limit value (20 μg/m³), not to be exceeded more than 7 times in any calendar year	50% of limit value (10 μg/m³)

Sulphur dioxide

	Health protection	Ecosystem protection
Upper assessment threshold	60% of 24-hour limit value (75 μg/m³), not to be exceeded more than 3 times in any calendar year	60% of winter limit value (12 μg/m³)
Lower assessment threshold	40% of 24-hour limit value (50 μg/m³), not to be exceeded more than 3 times in any calendar year	40% of winter limit value (8 μg/m³)