Air pollutant units and conversion factors

Air pollutants are measured in various units. Find out about the units and how to convert them so you can compare our data with data from other sources.

Pollutants are measured in the following units:

  • particle concentrations – micrograms per cubic metre (µg/m3)
  • gases – parts per million (ppm) for CO and parts per hundred million (pphm) for others
  • NEPH or visibility – reported in units of 10-4 m-1, i.e., a NEPH value of 2.5 is actually equal to 2.5 x 10-4 m-1.

We report our concentrations referenced to a temperature of 0 degrees Celsius and an absolute pressure of 101.325 kilopascals. This conversion table will allow you to compare data in the OEH air quality monitoring reports with those from other sources.

Pollutant

to convert from …

to …

multiply by

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)

20.5

Nitrogen oxides (NOx)

pphm

µg/m3 (25°C)

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