Interpreting Air Quality Data

​​​​​​​​​​​​​The Base Line Air Network of EPA Tasmania (BLANkET) is a network of small air quality stations reporting near real-time indicative particle concentration data (e.g. from smoke or dust). The stations also collect and report meteorological data.​ 

The purpose of BLANkET is to obtain air quality data in Tasmania away from the major air stations at Hobart, Launceston and Devonport. It monitors smoke produced by planned burns each autumn, wood smoke produced in winter by domestic heaters, bushfire smoke in summer, and provides a general measure of air quality at other times.

​​What do you mean by ​​partic​le concentration data? What are PM10 and PM2.5?

In Tasmania, when we talk of air quality and particles we often mean woodsmoke. 

The particles in smoke are mostly small, under 1-millionth of a metre in diameter, and are composed of soot (carbon) and complex chemicals such as tars and related compounds. 

Other sources of particles are airborne dust (generated by both human and natural processes) and other aerosols (such as sea-salt aerosols, and aerosols from vehicle emissions and industrial processes). 

Particles are often referred to as PM10, meaning all particles with an aerodynamic diameter of up to 10 millionths of a metre, and PM2.5, which are particles up to 2.5 millionths of a metre in aerodynamic diameter. A measurement of PM10 will include the PM2.5 particles too. The smaller particles are potentially the most hazardous to human health, as they can be breathed in and can penetrate internal tissue more easily.

BLANkET provides real-time indicative data for PM10 and PM2.5.

Does high PM10 al​ways mean s​moke?

No, it doesn't. Smoke particles are small and will be included in both the PM10 and PM2.5 measure. 

Generally speaking, PM2.5 is a better indication of smoke than PM10.

If both PM10 and PM2.5 are high, with PM10 only slightly larger than PM2.5, the instrument is probably measuring smoke. If PM10 is high and PM2.5 is low it means there are few very fine particles in the current air sample, so the instrument may be measuring dust or sea salt aerosols.

To check for dust it is worth looking at the wind speed in the lower plot. High winds can raise dust and keep it airborne. Dusty air can be carried long distances by strong upper level winds even when surface winds are low, though this is less common in Tasmania than on the mainland of Australia or elsewhere.​

The About BLANkET​ page has further information about this topic, including an example comparing dust and smoke.

How do I interpret the data plots?

The top plot shows the air quality data. The PM10 and PM2.5 concentrations are given in micrograms per cubic metre. 

As discussed above PM2.5 is a better indicator of smoke than is PM10.

For the current day of data, the most recent measurements are also given in the box to the right of the plot.

 

PM2.5 is shown as the red triangle symbols in the air quality plots. PM2.5 values below 5 µg/m3 signify very clear air. On a smoky winter's evening in Hobart or Launceston PM2.5 may be near 50 µg/m3 or more for several hours.

The meteorological data plot shows the air temperature, relative humidity, wind speed, wind direction, daily rainfall and barometric pressure.​ 

Wind speed is given in kilometres per hour (km/hr). Wind direction is given in degrees. Zero degrees is a north wind, 90 degrees is an east wind, 180 degrees is a south wind, and 270 degrees is a west wind. Wind direction is divided by 10 before being plotted, so a wind direction of 18 units on the plot means 180 degrees, or a wind from the south.

The most recent meteorological data are shown in the box at the right of the plot.


Key:
T - air temperature

RH - relative humidity
WS - wind speed
WD - wind direction
RF - daily rainfall 
P - mean sea-level pressure (MSLP)

The meteorological data are provided as a guide to interpreting the air quality data. They should not be used in place of Bureau of Meteorology data for determining weather conditions in a given region.​

Health effects of smoke

Detailed information on the health effects of smoke is given on the Tasmanian Department of Health (DoH) website Air Quality page.

The Tasmanian Department of Health provides the following air quality health categories based on the hour-averaged PM2.5 value:​

Good: 0 to 9 micrograms per cubic metre
Fairly Good: 10 to 24 micrograms per cubic metre
Fairly Poor: 25 to 49  micrograms per cubic metre
Poor: 50 to 99 micrograms per cubic metre
Very Poor: 100 to 299 micrograms per cubic metre​
Extremely Poor: Over 300 micrograms per cubic metre​

See the Department of Health Track Air Quality page for more information (scroll to the bottom of the page for category information​).​

Further information

For more information about BLANkET, please visit the About BLANkET​ page.