How and why we monitor air pollution

Learn how we sample air and measure pollutants for reliable air quality monitoring.

The Department of Industry, Planning and Environment is accredited by the National Association of Testing Authorities for the operation and maintenance of various air quality instrumentation (accreditation number 14209). Where applicable, Standards Australia methods for ambient air monitoring are used. Technical information about the sampling methods and the analytical techniques used in air monitoring programs is outlined below for the major polllutants we measure. 

Except for the rural NSW network stations, which use low cost indicative monitors, Australian Standard methods listed below are used within the NSW DPIE network. 

Why we monitor air pollution

The standards for ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide and air particles (PM2.5 and PM10) are set by the National Environment Protection Council.

See Standards and goals for more information.

How we monitor

Indicative monitoring

Indicative monitoring is not formally defined in Australia. It is defined in the UK and this text uses terminologies based on the UK definitions.

Air quality instruments can be grouped into 4 classes: certified reference, certified equivalent, certified indicative, and indicative. The main difference is accuracy and repeatability of measurements and the cost of purchase and operation.

Although they are not certified for monitoring for legislative purposes, indicative and certified indicative monitors are very useful in reporting current air quality to the community. In NSW, two such instruments are used widely to measure air quality:

  • indicative particle monitors across the Rural Air Quality Network
  • certified indicative monitors used to report visibility across the Greater Metropolitan Region and Regional Air Quality Networks

Most of these instruments minimise the impact of fog by heating the air before measurement to evaporate water droplets. Air particles arising from smoke and dust are still measured.

More about

New South Wales Rural Air Quality Network

Measurement techniques

Air pollutants are measured by a variety of techniques, most involving drawing sample air into the analyser and determining the concentration of the pollutant in the air.

Sample air is drawn into a cell where a beam of ultraviolet light is passed through it to an ultraviolet detector. Some of the light is absorbed by ozone in the sample, the amount being proportional to the number of molecules present. The decrease in intensity between the transmitted light and that of the source is used to determine the ozone concentration in the sample (Australian Standard 3580.6.1).

Sample air is drawn into a reaction chamber where nitric oxide (NO) in the sample reacts with a stream of ozone produced by an ultraviolet lamp in dried air. The reaction produces light (chemiluminescence) in the wavelength range 600–3000 nanometres. The light intensity, measured by a photomultiplier tube, is proportional to the concentration of nitric oxide. Total nitrogen oxides (NOx) concentration is measured in a separate sample stream by first reducing to nitric oxide (NO) using a selective converter. The concentration of nitrogen dioxide (NO2) reported is assumed to be the difference between total nitrogen oxides and nitric oxide (Australian Standard 3580.5.1).

A stream of sample air is drawn through a cell where it is exposed to pulsed ultraviolet light, resulting in excitation of sulfur dioxide molecules. These molecules subsequently re-emit light but at a different wavelength; they fluoresce. The intensity of the fluorescent light measured by a photomultiplier tube is proportional to the concentration of sulfur dioxide in the sample air (Australian Standard 3580.4.1).

Sample air is drawn into a cell where a beam of infrared light is passed through it to a photodetector. Some of the light is absorbed by carbon monoxide in the sample, the amount being proportional to the number of molecules present. By comparing the light intensity received by the photodetector through the sample cell with that received through a similar cell containing reference gas, the concentration of carbon monoxide may be determined (Australian Standard 3580.7.1).

  • Tapered Element Oscillating Microbalance (TEOM)
    The TEOM consists of a sensor unit which contains the sample inlet (PM10) and the TEOM microbalance for mass measurement. The TEOM microbalance consists of a filter which is held on the end of a tapered tube that oscillates upon particle impaction. As particles land on the filter, the filter mass change is detected as a frequency change in the oscillation of the tapered tube. The control unit of the TEOM houses the processing hardware and flow components. Combining the mass change with the flow rate through the system gives a measure of particulate concentration. The TEOM computes total mass accumulation on the filter as well as 30-minute, 1-hour and 8-hour mass concentration averages. It is therefore capable of providing continuous, real-time data (Australian Standard 3580.9.8).
  • TEOM-Filter Dynamic Measurement System (TEOM-FDMS)
    A TEOM-FDMS is used for the continuous, simultaneous monitoring of PM2.5 and PM10 at selected stations, particularly in regional New South Wales. This method (Australian Standard AS/NZS 3580.9.13) also provides continuous, real-time data. Instrument operational principles are discussed in the glossary.

Measurement technique: Beta Attenuation Monitor (BAM)

The BAM is a USEPA Federal Equivalent Method used for routine continuous PM2.5 monitoring. It draws air through a cyclonic inlet, accumulating PM2.5 particles onto a glass fibre filter tape. On saturation, the filter tape advances to provide a clean filter surface. High-energy beta radiation is passed through a defined spot on the filter and the intensity of radiation absorbed measured. Beta attenuation or the loss in beta signal through the filter is proportional to the mass of deposited particles. This, combined with the volume of air sample is used to calculate mass concentration (Australian Standard 3580.9.12). 

Measurement technique: BGI low volume sampler (Australian Standard 3580.9.10)

A USEPA Reference Method, this technique is used to meet NEPM regulatory monitoring requirements for PM2.5. Air is drawn through a cyclonic inlet that makes use of the aerodynamics of particles of different sizes to selectively capture those below 2.5 µm. A pre-conditioned Teflon filter paper, weighed before and after sampling provides 24 hour PM2.5 mass concentrations.

Ammonia (NH3) is measured with the same instrument as used for nitrogen oxides (NOx) by way of a modification which converts ammonia to nitric oxide (NO). The nitric oxide (NO) and ozone then react to produce a characteristic luminescence. The ammonia analyser has three active channels or modes: total nitrogen (Nt  = NO + NO2 + NH3), total nitrogen oxides (NOx = NO + NO2), and nitric oxide (NO). The ammonia concentration is determined by subtracting the NOx mode signal from the Nt mode signal.

To measure visibility or suspended matter, a sample of air, having been heated to eliminate any water droplets (fog), is continuously drawn through a sample cell. A beam of light of wavelength 530 nanometres is used to illuminate the air stream. Suspended fine particles in the air cause some of this light to be scattered. A photomultiplier tube, at right angles to the direction of the light coming in, produces a signal proportional to the intensity of the scattered light. The method detects particles about 0.1–2.0 micrometres (0.1 µm–2.0 µm) in diameter (Australian Standard 3580.12.1).