The Air Quality (Ozone) (Wales) Regulations 2003

Assessment of levels of ozone and ozone precursor substances

4.—(1) The National Assembly must ensure that levels of ozone and ozone precursor substances are assessed in each zone in accordance with this regulation.

(2) Continuous fixed measurement must be used in any zone in which, within any of the previous five years, levels of ozone have exceeded a long-term objective.

(3) In order to determine whether, during any of the previous five years, levels of ozone have exceeded a long-term objective in a zone in relation to which data from continuous fixed measurement is not available for the whole of that period, measurement campaigns of short duration, at times and locations likely to be typical of the highest pollution levels, may be combined with results from emission inventories and modelling.

(4) Where levels of ozone in a zone have not, in any of the previous five years, exceeded the long-term objectives, a combination of continuous fixed measurement, modelling and indicative measurements may be used in that zone.

(5)  For each zone to which paragraph (2) applies, the minimum number of sampling points for fixed continuous measurement must be in accordance with Part I of Schedule 3.

(6) For each zone to which paragraph (2) applies, measurements of nitrogen dioxide —

(a) must be made at a minimum of 50 per cent of the ozone sampling points required under Part I of Schedule 3;

(b) must be continuous, except at rural background stations, where other measurement methods may be used.

(7) The number of fixed sampling points required under paragraph (5) may be reduced provided that —

(a) the information from fixed sampling points is supplemented by information from modelling, indicative measurements or both these methods;

(b) the supplementary sources of information referred to in sub-paragraph (a) provide an adequate level of information for the assessment of air quality with regard to target values, information and alert thresholds;

(c) the number of sampling points to be installed and the spatial resolution of other techniques are sufficient for the level of ozone to be established in accordance with the data quality objectives specified in Part I of Schedule 5 and lead to assessment results as specified in Part II of that Schedule;

(d) the number of sampling points in each zone amounts to at least one sampling point per two million inhabitants, or one sampling point per 50,000 km², whichever produces the greater number of sampling points;

(e) each zone contains at least one sampling point; and

(f) nitrogen dioxide is measured at all remaining sampling points except at rural background stations.

(8) For each zone to which paragraph (7) applies, the supplementary sources of information referred to in paragraph (7)(a) must be taken into account when assessing air quality with respect to target values.

(9) For each zone to which paragraph (4) applies, the minimum number of sampling points for fixed measurements must be in accordance with Part II of Schedule 3.

(10) Schedule 2 has effect for the purpose of determining the location of sampling points for the measurement of ozone.

(11) The reference methods for the analysis of ozone and the calibration of ozone instruments set out in Schedule 6 must be used unless the National Assembly adopts other methods which it considers can be demonstrated to give equivalent results.

(12) For ozone precursor substances, —

(a) the National Assembly must ensure that at least one measuring station to supply data on levels of the ozone precursor substances listed in Schedule 4 is installed and operated within Wales; and

(b) in choosing the number and siting of the stations at which levels of ozone precursor substances are to be measured, the National Assembly must take account of the objectives, methods and recommendations laid down in that Schedule.

(13) For ozone and nitrogen oxides measurements of volume must be standardised at a temperature of 293 K and a pressure of 101.3kPa.