The Air Quality Limit Values (Wales) Regulations 2001

Regulation 5(5)

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 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 )

(c) PARTICULATE MATTER(1)

	24-hour average	Annual average
Upper assessment threshold	60 % of limit (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 2 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 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 information from emission inventories and modelling to determine exceedances of the upper and lower assessment thresholds.

(1)

The upper and lower assessment thresholds for PM₁₀ are based on the following indicative limit values for 1 January 2010, which will be reviewed in the light of further information on health and environmental effects, technical feasibility and experience in the application of the existing “Stage 1” limit values:

	Averaging Period	Limit value	Margin of tolerance	Date by which limit value is to be met
1.  24-hour limit value for the protection of human health	24 hours	50μg/m3 PM10 not to be exceeded more than 7 times a calendar year	To be derived from date and to be equivalent to Stage 1 limit value	1 January 2010
2.  Annual limit value for the protection of human health	Calendar year	20μg/m3 PM10	50% on 1 January 2005 reducing every 12 months thereafter by equal percentages to reach 0% by 1 January 2010	1 January 2010