The Air Quality Limit Values Regulations 2001

Regulations 5(5) and 6(1)

SCHEDULE 2 UPPER AND LOWER ASSESSMENT THRESHOLDS AND EXCEEDANCES

PART I Upper and lower assessment thresholds

The following upper and lower assessment thresholds will apply:

(a)

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)

(b)

NITROGEN DIOXIDE AND OXIDES OF NITROGEN

	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 value	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 value	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)

(c)

PARTICULATE MATTER

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

(d)

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)

PART II Determination of exceedances of upper and lower assessment thresholds

Exceedances of upper and lower assessment thresholds must be determined on the basis of concentrations during the previous five years where sufficient data are available. An assessment threshold will be deemed to have been exceeded if during those five years the total number of exceedances of the numerical concentration of the threshold is more than three times the number of exceedances allowed each year.

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 pollution levels may be combined with results obtained from emisson inventories and modelling to determine exceedances of the upper and lower assessment thresholds.