# The Air Quality Limit Values (Wales) Regulations 2001, 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
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 )

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Source: https://www.legislation.gov.uk/wsi/2001/2683/schedule/2/part/I (the official version)
Page: https://openlegislation.uk/air-quality-limit-values-wales-regulations-2001/schedule-2/part-I
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.