Upper Hunter air quality monitoring network - what is measured

The Upper Hunter Air Quality Monitoring Network (UHAQMN) is the regional air quality monitoring network in the Upper Hunter Region.

Why do we need the UHAQMN?

In 2009 and 2010 there was a high level of community concern about the cumulative impact of coal mining on air quality in the Upper Hunter Region. The UHAQMN was established in October 2010 to provide reliable, regional air quality monitoring data. By February 2012, fourteen monitoring sites were operational in strategic locations, including the major population centres of Singleton and Muswellbrook. All these monitoring sites measure particulates (dust), and some also measure sulphur dioxide (SO2) and oxides of nitrogen (NOx).

The air quality data that is collected through the network is available to the public in close to real time, with mobile phone text alerts being sent to subscribers when the air quality is ‘poor’. Current monitoring results from the UHAQMN are updated hourly.

The air quality web pages allow the community to access close to real-time data from the 14 station UHAQMN.

What is being measured in the UHAQMN?

All monitoring stations report on:

  • particles as PM10 (particles with a diameter of 10 micrometres (µm) or smaller)
  • wind speed
  • wind direction.

Three of these stations (Muswellbrook, Singleton and Camberwell) also report on particles 2.5 µm or smaller (PM2.5).

What are particles?

Particles (also known as 'particulate matter' or PM) is the term used for a mixture of solid particles and liquid droplets suspended in the air. The particles are made up of a number of components, including nitrates and sulfates, organic chemicals, metals and soil or dust particles. Some particles, such as dust, dirt, soot or smoke, are large or dark enough to be seen by the naked eye. Others are so small that they are invisible.

Particle pollution includes particles with diameters that are 10 µm or smaller (including particles smaller than 2.5 µm) and these are designated as PM10. Particles from vehicles on dirt roads and dusty industries, such as mining, crushing and grinding, are generally larger than 2.5 µm in diameter and are included in PM10.

Other smaller particles or 'fine particles' are those with diameters that are 2.5 µm or smaller (designated as PM2.5) and are commonly found in smoke and haze. 

For comparison, the average human hair is about 70 µm in diameter, making it some 30 times larger than the PM2.5 particles measured in the UHAQMN. Air pollution - Particulate matter (PM2.5) provides additional information on fine particles. 

How are particles formed?

Some particles are natural while others are generated by human activity. Natural sources include bushfires, dust storms, pollens and sea spray.

Particles generated by human activity can be emitted from sources such as motor vehicles, power plants, mining and materials handling, residential wood burning, agricultural burning, and some industrial processes; these are known as primary particles. Others are formed in complicated reactions in the atmosphere from chemicals such as sulfur dioxide and oxides of nitrogen emitted from power plants, industries and motor vehicles and are known as secondary particles.

How do particles move?

Large particles in the air usually cause reduced visibility for a short time and settle close to their source. 

Small or fine particles can remain in the atmosphere for several days and be transported great distances from their source by the wind. They are capable of scattering light which also leads to a reduction in visibility.

Particles are generally removed from the atmosphere by rain or when they come into contact with surfaces.

How do particles impact on people?

Visibility reduction

Fine particles (PM2.5) are the major cause of reduced visibility in parts of NSW and hence have an impact on our enjoyment of the environment. They can also cause nuisance when they deposit out and soil homes, buildings and other surfaces.

Health effects

While most healthy people can breathe in small amounts of particles without major long-term effects, extreme air pollution events such as bushfires and major dust storms can affect everyone.  Some people  (eg children, those with heart or lung disease and the elderly) can be sensitive to even relatively low levels of particle pollution.

Exposure to fine particle pollution has been linked to a variety of health problems including Increased respiratory symptoms (e.g. irritation of the airways, coughing or difficulty breathing), heart problems and premature death in people with heart or lung disease.

Health effects depend on a number of factors, including:

  • particle size
  • intensity and duration of exposure
  • the chemical nature of the particles
  • a person’s health and
  • weather conditions, including wind, humidity and rainfall.

You can find more information on the health effects of fine particles at the NSW Department of Health web site.

How are particles measured in the UHAQMN?

Two methods can be used to collect air quality data: the ‘reference’ methodology and the ‘continuous monitoring’ methodology.

Reference methods involve batch collection of fine particles on filter paper over 24 hours: samples are collected and then transported to special laboratory facilities for weighing and reporting of results. This process can take 2-3 weeks. Because of the time-lag associated with this, we have chosen suitably recognised, continuous methodologies to provide the continuous record of data for the web-based community reporting and alert systems operated by OEH.

Two different types of continuous monitoring instrument are used as part of the UHAQMN: one measuring PM10 and one PM2.5. Both have been recognised as Federal Equivalent Methods (FEM) by the US EPA.

Measurement of PM10

The Tapered Element Oscillating Microbalance (TEOM) instrument was chosen for the continuous measurement of PM10. A TEOM will be located in each of the 14 stations making up the UHAQMN.

These instruments fitted with a size-selective PM10 inlet draw (then heat to counter humidity) a constant volume of ambient air through a filter which is mounted on a vibrating hollow glass tube (the tapered element). Particles are collected on the filter, which then increases in weight. This additional weight changes how often the tapered element vibrates (or oscillates) from one side to the other.

The mass of the particles is determined by the change in oscillation frequency. The mass is divided by the volume of air sampled by the instrument over the same time period to produce the mass/unit volume (micrograms/cubic metre - µg/m3).

Because the particles can include water (via rain or humidity) as part of their mass, it is important that the inlet is heated (to 30-50 degrees C) to dry out the particles before they land on the filter.

The TEOMs operate on a continuous basis and the data averaged over one hour is assembled and transmitted to the OEH data centre for further processing and posting on the OEH website (hourly updates).

Measurement of PM2.5

The Beta Attenuation Monitor (BAM) was chosen for the continuous measurement of PM2.5. Three BAMs will be located in the UHAQMN at Singleton, Muswellbrook and Camberwell.

These instruments are fitted with size-selective inlets and very sharp cut cyclones (VSCC) to collect the PM2.5 sample stream which is then heated (to reduce the effects of humidity) and passed through a filter tape. The amount of heating is determined by the humidity levels of the incoming sample stream.

The particles are deposited onto the glass fibre tape and then the particle mass is irradiated with beta radiation. Fine particle mass is proportional to the attenuation of this radiation through a known sample area to continuously collect and detect the measured mass.

The simultaneous mass measurements of particles on the filter tape and sample volume measurement through a calibrated orifice provide a continuous concentration measurement in micrograms/cubic metre. As described earlier for the continuous TEOM PM10 data, the hourly averaged PM2.5 data is collected and posted onto the OEH website on an hourly basis.

How can we be sure the data posted by the UHAQMN is reliable?

It is important that the monitoring equipment used is appropriately accredited (e.g. compliance with local or international standards), properly installed and regularly calibrated and serviced to ensure it is providing accurate and reliable data.

The instruments used meet international (USEPA Federal Equivalent Methods) and the relevant Australian Standards.

OEH, which has built and is operating the UHAQMN, is accredited by the National Authority of Testing Authorities (NATA) for the operation and maintenance of these monitoring stations and associated equipment.

Once fully installed, the UHAQMN will undergo independent peer review of all its operating and calibration procedures.

Why are there gaps in data or no results on the website?

The UHAQMN is operated to maximise the online time. Because of the need for regular maintenance and calibration, the network is not online 100% of the time. With about 5% of time lost due to routine maintenance and calibration schedules, 95% is the target online time. These schedules comply with the requirements of the relevant Standards for servicing the equipment.

Under NEPM guidelines, an 'average' is deemed valid only when at least 75% of data during the averaging period is valid (e.g. a valid 24-hour average is only calculated from at least 18 valid hourly averages).

Gaps in data can be due to:

  1. Scheduled maintenance and calibration where the following are carried out on a regular basis:
    • Quarterly - Clean sample head and inlet and replace filters; leak check (1-2 hrs)
    • 6-monthly - Flow audit (1-2hrs)
    • Annual - software (1-2 hrs) and hardware calibration (1-2 hrs); zero stability check (at least 8 hrs); site audit (1-2 hrs)
  2. Equipment failure at site or communications failure between instrument and data logger(variable)
    Data are lost for either of these reasons - there will be gaps in the database and on the web.
  3. Power Outages at site (variable): Data is lost as equipment is powered off during the outage.
  4. Telecommunication problems (variable): Data will not be loaded to the web site during this period, however, the data is not lost but downloaded to the database and uploaded to the web once communication is re-established. 
  5. Website maintenance (variable): Data is not lost as it is stored locally until the website is up and running again.
Page last updated: 13 November 2015