Concentration values are the primary measurements of parameters obtained from air quality monitoring stations. Concentrations are reported as:
- particles (as PM10, PM2.5) – micrograms per cubic metre (µg/m3)
- NEPH or visibility – while commonly written as 'bsp' NEPH is reported in units of 10-4 m-1. This means that a NEPH value of 1.5 should be read as 1.5x10-4 m-1. On multiplying by 100 you can convert this number to the widely used unit for visibility known as inverse megametres (Mm-1).
- gases – parts per million (ppm) for CO and parts per hundred million (pphm) for others. Gaseous concentration values are reported referenced to a temperature of 0°C and an absolute pressure of 101.325 kilopascals. This conversion table will allow you to compare data in the department's air quality monitoring reports with those from other sources.
Visit the air quality glossary for detailed definitions of concentration reporting terminology.
| Pollutant | Concentration units we report in … | to convert from our reported units to … | multiply by |
|---|---|---|---|
| Ammonia | pphm | µg/m3 (0°C) µg/m3 (25°C) | 7.6 7.0 |
| Ozone | pphm | µg/m3 (0°C) µg/m3 (25°C) | 21.4 19.6 |
| Nitric oxide (NO) | pphm | µg/m3 (0°C) µg/m3 (25°C) | 13.4 12.3 |
| Nitrogen dioxide (NO2) | pphm | µg/m3 (0°C) µg/m3 (25°C) | 20.5 18.8 |
| Sulfur dioxide (SO2) | pphm | µg/m3 (0°C) µg/m3 (25°C) | 28.6 26.2 |
| Lead | µg/m3 (0°C) | µg/m3 (25°C) | 0.92 |
| Carbon monoxide | ppm | mg/m3 (0°C) mg/m3 (25°C) | 1.25 1.15 |
| NEPH or visibility | 10-4 m-1 | Mm-1 or inverse megametres | 100 |
Air quality category colours
Air quality categories are expressed using a colour rating as well as numbers.