Regulation 12
SCHEDULE 2Monitoring stations
Site descriptions: interpretation
1. In this Schedule, the following descriptions of sites of monitoring stations have the following meanings—
“near-source” means a site in a location where the PM2.5 level is likely to be elevated above the background level due to the influence of one or more sources of pollution in close proximity to the site, such as emissions from traffic from a major road or from nearby industrial sources;
“suburban background” means a site—
in a partially built-up area which is mixed with non-urbanised areas; and
where the PM2.5 level is not significantly influenced by a source or sources of pollution in close proximity to the site, and is therefore representative of the background level of PM2.5 to which the population is likely to be exposed across a wider area than the immediate vicinity of the site;
“urban background” means a site—
in a continuously or predominantly built-up area which is not mixed with any non-urbanised areas except for urban parks; and
where the PM2.5 level is not significantly influenced by a source or sources of pollution in close proximity to the site, and is therefore representative of the background level of PM2.5 to which the population is likely to be exposed across a wider area than the immediate vicinity of the site.
Location of monitoring stations
2.—(1) All monitoring stations must be located at a site which—
(a)is in, or representative of, an area to which members of the public or a section of the public have access and are likely to frequent;
(b)is not within the boundary of a factory or other industrial premises;
(c)is not on the carriageway of a road, or on a central reservation of a road to which there is not normally pedestrian access.
(2) Subject to complying with sub-paragraph (1), and to the requirements in paragraphs 4 and 5, a monitoring station may be located at a site of any description (and not only at a site of a description in paragraph 1).
Minimum numbers of monitoring stations
3.—(1) Until 31st December 2027—
(a)the total number of monitoring stations in each zone must be not less than the number of AQSR monitoring stations in that zone immediately before the coming into force of these Regulations;
(b)at least one monitoring station in each zone must be at an urban background or suburban background site.
(2) From 1st January 2028—
(a)the total number of monitoring stations in each zone, and
(b)the number of those monitoring stations which are—
(i)at urban background or suburban background sites;
(ii)at near-source sites,
must be not less than the minimum numbers specified in the following table.
| Population of zone (thousands) | Minimum total number of monitoring stations | Minimum number of monitoring stations at urban background or suburban background sites | Minimum number of monitoring stations at near-source sites |
|---|---|---|---|
| ≥ 6,000 | 15 | 10 | 5 |
| 4,750 – 5,999 | 11 | 7 | 4 |
| 3,750 – 4,749 | 10 | 6 | 4 |
| 2,750 – 3,749 | 9 | 6 | 3 |
| 1,000 – 2,749 | 6 | 4 | 2 |
| 250 – 999 | 3 | 2 | 1 |
| <250 | 2 | 1 | 1 |
Siting criteria
4.—(1) Monitoring stations must be sited in accordance with the criteria in sub-paragraphs (2) to (4).
(2) Monitoring stations must be sited to avoid measuring PM2.5 levels within very small micro-environments in their immediate vicinity.
(3) Monitoring stations at near-source sites, as a group, must include stations which are sited to provide data that are representative of locations where the highest PM2.5 concentrations are likely to occur to which the population is exposed for significant periods.
(4) Monitoring stations at near-source sites where the main nearby source of pollution is traffic emissions from a road must be—
(a)not more than 10 metres from the kerbside of the road;
(b)not less than 25 metres from the edge of any junction which interrupts the traffic flow and causes different levels of vehicular PM2.5 emissions from the rest of the road; and
(c)representative of PM2.5 levels in a length of the road of not less than 100 metres.
Position of monitoring equipment
5. Equipment for measuring PM2.5 levels at monitoring stations must be positioned in accordance with the following criteria—
(a)the flow of air around the sampling inlet must be unrestricted (free in an arc of at least 180° if the equipment is affixed or adjacent to a building or 270° otherwise);
(b)the sampling inlet must—
(i)be not less than 0.5 metres from the nearest building, tree or other obstacle; and
(ii)not be positioned in the immediate vicinity of a source of PM2.5 emissions;
(c)the height of the inlet sampling probe must be not less than 1.5 metres and not more than 8 metres above the ground;
(d)the sampler’s exhaust outlet must be positioned so that recirculation of exhaust air to the sampler inlet is avoided.