Ambient air reports are full of acronyms. Here is what the main ones mean and how to read the numbers.
Particulate matter: PM10 and PM2.5
PM10 is particles up to 10 micrometres across — dust, pollen, construction debris. PM2.5 is the fine fraction, 2.5 micrometres and smaller, which penetrates deep into the lungs. Both are reported as a mass concentration in micrograms per cubic metre (µg/m³), averaged over 24 hours or a year.
Gases
- NO2 — mostly from combustion and traffic
- SO2 — from sulphur-containing fuels
- O3 — ground-level ozone, formed in sunlight
- CO — incomplete combustion
The Air Quality Index (AQI)
The AQI converts several pollutant concentrations into a single 0–500 scale with colour bands, so a non-specialist can see at a glance whether air is “good” or “unhealthy”. The reported AQI is driven by whichever pollutant is worst at that moment.
Reading your site report
- Check the averaging period — a high one-hour value is not the same as a high annual mean
- Compare against the limit that applies (national standard or lender/IFC guideline)
- Look at how many valid data hours the average is based on
- Note the monitor location relative to sources and receptors
EnviraH designs and runs ambient monitoring campaigns and delivers reports you can put in front of a regulator or a lender. Environmental monitoring.
