The Air Quality Standards Regulations 2007 (revoked)

Regulation 13(6)

SCHEDULE 4 U.K. Assessment thresholds

PART 1 U.K. 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)

PART 2 U.K. Assessment thresholds for Group B pollutants

Arsenic

Upper assessment threshold	60% of target value (3.6 ng/m3)
Lower assessment threshold	40% of target value (2.4 ng/m3)

Benzo(a)pyrene

Upper assessment threshold	60% of target value (0.6 ng/m3)
Lower assessment threshold	40% of target value (0.4 ng/m3)

Cadmium

Upper assessment threshold	60% of target value (3 ng/m3)
Lower assessment threshold	40% of target value (2 ng/m3)

Nickel

Upper assessment threshold	70% of target value (14 ng/m3)
Lower assessment threshold	50% of target value (10 ng/m3)

PART 3 U.K. Determination of representative concentrations

1.  The representative concentration of the relevant pollutant shall be determined on the basis of concentrations during the previous five years where sufficient data are available. The upper assessment threshold will be deemed to have been exceeded if it has been exceeded during at least three separate years out of the previous five years. Similarly, the lower assessment threshold will be deemed to have been equalled or exceeded if it has been equally or exceeded during at least three separate years out of the previous five years. U.K.

2.  Where fewer than five years' data are available, measurement campaigns of short duration during the period of the year and at locations likely to be typical of the highest concentrations may be combined with results obtained from emission inventories and modelling to determine exceedances of the upper and lower assessment thresholds. U.K.