Frequently Asked Questions
Air pollution is a complex topic that can sometimes be difficult to understand due to its scientific nature. This FAQ addresses common questions about air pollution monitoring, the most prevalent pollutants, their sources, and their potential health impacts.
If you don’t see your question listed here, please email us and we’ll do our best to include it in our FAQs as soon as possible.
Frequently Asked Questions
All data displayed on this site are derived from 15‑minute “raw” measurements that have been automatically edited to remove calibration periods. Every night between 00:30 and 01:00 GMT, each gas analyser performs an automatic calibration. Those calibration readings are excluded from public charts (but retained internally for quality assurance) and replaced with zero values for each 15‑minute interval. On the 24‑hour chart, you’ll see these zero points clearly because it plots every 15‑minute measurement.
If you expand the chart’s timeframe to cover two or more days, the data are shown as hourly averages — in that view, individual calibration zeros become part of the aggregated hourly value and are not displayed separately.
Legislative Background
Part IV of the Environment Act 1995 requires every local authority to review and assess air quality against health‑based objectives defined in the National Air Quality Strategy (NAQS). First published in March 1997, the NAQS sets legally binding standards for seven key pollutants. In Wales, the original Air Quality Regulations 1997 were superseded by the Air Quality (Wales) Regulations 2000 and amended by the Air Quality (Amendment) (Wales) Regulations 2002.
Swansea’s Review & AQMA Declaration
Swansea’s first Stage 1 review (1999) identified potential exceedances of benzene, PM₁₀, sulphur dioxide (SO₂), and nitrogen dioxide (NO₂). Subsequent Stage 2 and Stage 3 assessments determined that only NO₂ concentrations in parts of Hafod were likely to breach the annual mean objective of 40 µg/m³ by the December 2005 compliance date. As a result, the City & County of Swansea declared the Hafod Air Quality Management Area (AQMA) on 12 September 2001 (effective 14 September 2001). A Stage 4 review confirmed that this designation remained justified.
Action Plan & Ongoing Assessment
Under Section 84 of the Environment Act 1995, local authorities must produce an Action Plan to achieve air quality objectives within designated AQMAs. Swansea’s Hafod AQMA Action Plan is currently under development.
The national review process has now entered its second round, comprising:
- Updating & Screening Assessment – Identifies changes since the first review and flags pollutants requiring further work
- Detailed Assessment – Investigates those pollutants in greater depth and recommends mitigation measures
What are the key air quality pollutants?
The Air Quality (Wales) Regulations 2000 and Air Quality (Amendment)(Wales) Regulations 2002 set air quality objectives for the 7 key pollutants contained within the UK National Air Quality Strategy. The current air quality objectives set in regulation are listed below:
| Pollutant | Concentration | Measured as | Examples of sources | Permitted number of exceedences allowed | Compliance date |
| Benzene*(C6 H6) | 16.25 µg/m3 (5ppb) | Running annual mean | Constituent of petrol emitted as un-burnt fuel or through evaporation (motor vehicles etc). Also present in cigarette smoke. |
n/a
|
31 Dec 2003 |
| 5 µg/m3 (1.5ppb) | Annual mean |
n/a
|
31 Dec 2010 | ||
| 1,3-Butadiene* | 2.25 µg/m3 (1 ppb) | Running annual mean | Used in the manufacture of synthetic chemicals and rubber. Also present in cigarette smoke. |
n/a
|
31 Dec 2003 |
| Carbon monoxide (CO) | 10.00 m g/m3 (8.6ppm) | Maximum daily running 8 hour mean | Vehicle emissions, inefficient combustion of most fuels including gas, coal and oil. |
n/a
|
31 Dec 2003 |
| Nitrogen dioxide (NO2) |
200 µg/m3 (105ppb) | 1 hour mean | Combustion processes particularly vehicle emissions. |
18
|
31 Dec 2005 |
| 40 µg/m3 (21ppb) | Annual mean |
n/a
|
31 Dec 2005 | ||
| Lead (pB) |
0.5 µg/m3 | Annual mean | Main source in ambient air from leaded petrol (4 Star) |
n/a
|
31 Dec 2004 |
| 0.25 µg/m3 | Annual mean ( by 2008) |
n/a
|
31 Dec 2008 | ||
| Particles (PM 10) |
50 µg/m3 | 24 hour mean | Many sources but particularly from diesel vehicle emissions in towns and cities. |
35
|
31 Dec 2004 |
| 40 µg/m3 | Annual mean |
n/a
|
31 Dec 2004 | ||
| Sulphur dioxide (SO2) |
350 µg/m3 (132 ppb) | 1 hour mean | Mainly from combustion of fossil fuels. |
24
|
31 Dec 2004 |
| 125 µg/m3 (47 ppb) | 24 hour mean |
3
|
31 Dec 2004 | ||
| 266 µg/m3 (100 ppb) | 15 minute mean |
35
|
31 Dec 2005 | ||
| Key µg/m3 = (microgram per cubic metre of air) mg/m3 = (milligram per cubic metre of air) ppb = (part per billion) or one part of the pollutant per one billion parts of air. ppm = (part per million) or one part of the pollutant per million parts of air. |
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