What is BLANkET?
The Base Line Air Network of EPA Tasmania (BLANkET) is a network of 29 small air quality stations reporting near real-time indicative particle concentration data (i.e. from smoke or dust) to the EPA Division's public web pages. The stations will also collect and report meteorological data (air temperature, wind speed, etc.).
What is its purpose?
The purpose is to obtain air quality data in Tasmania away from the
existing air stations at Hobart, Launceston, and George Town. In particular it will monitor the spatial extent of smoke events produced by planned burns each autumn, but will also be used (in some localities) to monitor wood smoke produced in winter by domestic heaters, bushfire smoke in summer, and to provide a general measure of air quality at other times.
12 February 2009: BLANkET project approved
06 May 2009: Derby and Lilydale stations commissioned.
13 May 2009: BLANkET launch by Minister Michelle O'Byrne at Lilydale. Scottsdale station commissioned.
20 May 2009: St Helens and Fingal stations commissioned.
30 November 2009: Huonville, Geeveston and Judbury stations commissioned.
17 February 2010: Site preparation completed at Exeter (mid Tamar
valley), and nearly complete at Bryn Estyn and Gretna (mid Derwent
18 February 2010: Exeter station commissioned. Site works commenced near Burnie, Ulverstone and
23 February 2010: Bryn Estyn and Gretna stations commissioned.
25 February 2010: West Ulverstone and Emu River (near Burnie) stations commissioned.
26 February 2010: Sheffield station installed, awaiting electical power connection.
17 March 2010: Sheffield station on-line.
23 March 2010: Site selection has been finalised and site preparation is soon to start at Carrick in the lower Meander valley.
24 March 2010: Site preparation completed at Carrick.
25 March 2010: Station installed at Carrick and on-line.
16 July 2010: A BLANkET station was commissioned at Clearys Gates (Hobart) as part of the Air Toxics program.
21 July 2010: A second Air Toxics BLANkET station was commissioned at South Launceston.
24 March 2011:Smithton station installed and on-line.
25 March 2011: Wynyard station installed and on-line.
14 July 2011: BLANkET instrumentation commissioned at the George Town Air Monitoring Station (GAMS), funded through the GAMS partners of local
industry, local government, and the EPA Division.
14 March 2012: 'BLANkET' DRX instrument installed at Launceston Ti Tree Bend air station.
21 August 2012: New Norfolk BLANkET station installed and operational.
31 August 2012: Campbell Town station installed. Power connected and operational 10 September 2012.
30 January 2013: Hadspen station deployed and operational.
6 February 2013: Westbury and Deloraine stations deployed and operational. Longford station installed, awaiting power connection.
12 February 2013: Clearys Gates station closed and removed. Station will be re-deployed at another location after maintenance.
13 February 2013: Power connection at Longford - awaiting station visit for checks and power on. Carrick station closed and removed. It also will be redeployed at another location after maintenance.
18 February 2013: Longford station on-line.
17 May 2013: Perth station installed and operating.
25 June 2013: Mornington experimental solar-powered station commissioned.
08 November 2013: 'BLANkET' DRX instrument installed at Devonport air station.
18 March 2014: A second solar-powered station was deployed at Penguin for the autumn planned burn season.
04 June 2014: Penguin station relocated to Ulverstone for winter 2014.
02 July 2014: Deloraine Station removed for redeployment for campaign monitoring in Burnie and elsewhere.
03 July 2014: Bream Creek (Copping) station established through funding from Southern Waste Solutions.
31 October 2014: Ulverstone station moved to Poatina for an approximate 12-month monitoring campaign.
June 2015: EPA Tasmania is part of a consortium that was successful in obtaining funding through Sense-T, at the University of Tasmania, for the 'AirRater' project. The grant will fund five new BLANkET stations and other air quality initiatives.
What do you mean by particle 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 meter, and PM2.5, which are particles up to 2.5 millionths of a meter in aerodynamic diameter. By definition, a measurement of PM10 will include the PM2.5 particles too. BLANkET will provide real-time indicative data for PM10 and PM2.5. The smaller particles are potentially the most hazardous to human health, as they can breathed in and can penetrate internal tissue more easily.
Does high PM10 always mean smoke?
No, it doesn't. As noted above, smoke particles are small, and will be included in both the PM10 and PM2.5 measure. 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 fine particles in the current air sample, and the instrument may be measuring dust or sea salt aerosols.
To check for dust it is worth looking at the meteorological data in the
lower panel which shows wind speeds, as high winds can raise dust and
keep it airborne. Note that it is possible for dusty air to 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 graph below compares the signatures from dust (high PM10, relatively low PM2.5) and smoke (high PM2.5, with PM10 slightly higher than PM2.5) as seen at Scottsdale in September 2009. The peak of the dust event occurred late on the 12th of September. Around midday on the 14th of September some local (agricultural) burning took place near the BLANkET station.
On the reports page you can find a description of this dust-deposition event over Tasmania that occurred on the 12th of September 2009 - see BLANkET Technical Report 5.
Naturally occurring aerosols composed of sea-salt crystals can also give rise to high PM10 with very little increase in the PM2.5
level. These aerosols are liberated into the atmosphere during stormy
weather at sea, and can be transported over land by wind systems. On
the reports page you can find a description of an event lasting several
days in May 2009 when moderate north-easterly winds brought aerosol
laden air over Tasmania - see BLANkET Technical Report 4. Sea-salt aerosols can contribute to atmospheric haze. The BLANkET instruments can distinguish between smoke and sea-salt aerosols from a
comparison of the PM10 and PM2.5 levels.
Generally speaking, PM2.5 levels will be high during smoky intervals at a given station. For the reasons given above, PM2.5 is a better indication of smoke than PM10.
How do I interpret the plots of the data?
The top panel of the plots shows the air quality data. The PM10 and PM2.5 concentrations are given in micrograms per cubic metre (in short form this is written as µg/m3, or µg m-3 in scientific notation). For the current day of data, the most recent measurements are also given in the box to the right of the plot.
As discussed above PM2.5 is a better indicator of smoke than is PM10. PM2.5 is shown as the red square symbols in the air quality plots. PM2.5 values below 5 µg m-3 signify very clear air. On a smoky winter's evening in Hobart or Launceston PM2.5 may be near 50 µg m-3 for several hours.
The meteorological data plot shows the external (air) temperature and relative humidity, wind speed and wind direction, and daily rain fall ('RF') and barometric pressure. If you look carefully you can follow each line. Wind speed is given in kilometres per hour (km/hr, or km hr-1 in scientific notation). 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.
For the current day of data the most recent meteorological data are given numerically in the box at the right of the plot.
The meteorological data are provided as a guide to interpreting the air quality data. They should not be used in place of Bureau of Meteorological data for determining weather conditions in a given region.
What do you mean by indicative air quality data?
The BLANkET data are indicative data, not reference data. Reference
air quality data, collected in accordance with National and International standards, are obtained at the Hobart, Launceston and George Town stations using air samplers that collect particles onto a specially prepared filter. Each filter is exposed to ambient air for 24 hours. The filter is weighed before and after exposure, hence this is referred to as a gravimetric method. The increase in mass is found, which relates to the average particle levels in the air over those 24 hours. Reference data are used to assess whether exceedences of air quality standards have occurred. This gravimetric technique is a very precise method, but it cannot provide a real-time ("now") estimate of particle concentration.
The BLANkET data are being measured by an optical scattering method. In
essence, air is drawn into a cavity illuminated by a laser beam. The
more particles in the air, the more the laser light is scattered in the
cavity. A similar effect is familiar to us when driving at night in fog - the fog scatters the car headlights back towards the car. The thicker the fog, the more light is returned towards the car.
The particular instrument we are using for BLANkET is called a DRX Dustrak.
This optical method does not directly measure the mass concentration (which is the mass in a given volume) of the particles, but instead it measures a quantity related to the number of particles in a given volume of air. We have a calibration to convert from the number of particles to the total mass, based on assumed (usual) particle properties. However, because we are not measuring mass directly, the data remain indicative of the likely mass concentrations at the time so are not reference data.
We have used such an optical scattering instrument at the Launceston air quality station for a number of years, alongside reference gravimetric
instruments, and have found that, with care, they give reliable results. Hence we have chosen to use these instruments for the BLANkET monitoring program.
Why don't you use a reference method for BLANkET?
The advantages of the scattering instrument are that it is of relatively low cost, small in size, has a low power consumption, and operates almost entirely without needing human intervention. This means we are able to deploy many more such instruments than if we used the reference air samplers mentioned above. Additionally we obtain a real-time measure of air quality, rather than needing to pre-weigh, deploy, recover, and post-weigh a filter.
Gravimetric instruments are available that can give hourly (or even more
frequent) reference data. Again these are more expensive, and require
more complex (and expensive) supporting infrastructure. We use one type
of these sorts of instruments, known as a TEOM, at our major air
stations in Hobart and Launceston.
How good are these indicative data?
We have been comparing and cross-checking the performance of the BLANkET instrument against our reference instruments and will continue to do so. The graph below shows one such comparison, obtained at the New Town (Hobart) air station on the 16th of April 2009. The solid line shows data from the TEOM (which can be operated as a reference instrument), while the dotted line with the small points shows data from the BLANkET dustrak instrument. The indicative data shows good agreement with the TEOM measurements. A long series of tests, extending over several weeks, were performed prior to selecting the DRX dustrak
for use in BLANkET. The agreement between the TEOM and BLANkET instrument shown in the figure is representative of the test findings.
A comparison plot between TEOM PM10 and DRX dustrak PM10 data for 16 April 2009 at Hobart
The figure below shows a comparison of day-averaged DRX data and reference data from low-volume air samplers at New Town station for April to September 2010. The top panel shows PM10, the lower panel shows PM2.5. The blue triangles show the reference air sampler data, the red squares show the day-averaged DRX data. The agreement is generally very good, particularly for PM2.5.
A comparison of reference low-volume air sampler (blue
triangles) and day-averaged BLANkET (red squares) air quality data, for
New Town station, winter 2010 (Credit: EPA Division, 2010)
What are the national standards for PM10 and PM2.5?
The National Environmental Protection (Ambient Air Quality) Measure
(known as the Air NEPM) stipulates air quality standards in Australia. For PM10 there is a 24-hour standard of 50 µg m-3 (50 millionth of a gram per cubic metre). That is, if PM10 levels measured by a reference instrument, averaged over 24 hours, exceeds 50 µg m-3, an exceedence of the standard is recorded. The Air NEPM also
stipulates that the reporting interval is the calendar day (midnight to
midnight). For PM2.5, an advisory 24-hour reporting limit is set at 25 µg m-3. It is likely that this reporting limit will become a national standard in the future.
Currently there are no air quality standards for PM10 or PM2.5 for intervals shorter than 24-hours. That is, if PM10 levels exceed 50 µg m-3 for only one or two hours, but for the rest of the 24-hour interval PM10 levels are low so the day-average is below 50 µg m-3, then an exceedence would not be recorded. There is significant interest both in Australia and overseas in specifying PM10 and PM2.5 standards for intervals shorter than 24-hours. Such standards may be enacted in the future.
How will I know if air quality standards have been breached?
As noted above, the BLANkET indicative data cannot be used to determine if an air quality standard has been breached. The data will however provide a good indication of air quality at any given time, and hence provide an indication that, had a reference instrument been located at a given site, whether an air quality breach would have been likely to have been recorded.
What is a 'safe' level of smoke?
Detailed information on the health affects of smoke is given on the Tasmanian Department of Health and Human Services (DHHS) web site at www.dhhs.tas.gov.au/publichealth/air. A summary of health-related information is given here.
A number of health studies carried out both in Australia and overseas have clearly shown there is no 'safe' level of exposure to wood smoke. Any increase in particle levels a given population is exposed to will result in increases in, for example, hospital admissions for respiratory illnesses.
Those most at risk include people with respiratory conditions, the very
young, and the elderly, but other people in the wider population can
also experience medical problems.
The fine particles found in wood smoke are very difficult to remove from the air. During widespread smoke events it is very difficult for susceptible people to avoid exposure. Standard air conditioning equipment is not able to prevent the small smoke particles from entering domestic buildings.
How have the BLANkET sites been selected?
The sites were chosen to try to balance between having as broad a cover of as much of the state as possible, but not so broad as to spread the stations too thinly. Hence we have elected to place stations in the north-east, effectively surrounding the higher country where forestry operations take place, with another cluster in the upper Derwent and Huon regions. Both the north-east and the Huon and Derwent valleys have experienced smoke events in recent seasons.
Subsequently, a number of other stations have been deployed in the northwest and central north.
The BLANkET network will complement the existing major air quality
stations in Hobart and Launceston. A major air quality station is also in operation in Devonport.
Can you tell the differences between smoke from planned burns, bushfires, and domestic woodheaters?
There are likely to be small differences in particle type and chemical composition in smoke from a planned burn or bushfire compared to a domestic heater. The BLANkET instruments will not be able to measure this.
However there are other ways to address this question. When a relatively small amount of smoke is produced locally (such as from a nearby woodheater, or from a number of woodheaters), and is detected at a nearby station, the smoke is not well mixed with the air, but shows a lot of variation in the measured concentration. Conversely, if a large plume of smoke has travelled a number of kilometres from the source before reaching the station it has had time to become well mixed. The graphs below compare the two cases. The top panel shows two days of PM2.5 data from Lilydale BLANkET station in July 2009. There is significant variation between each measurement taken 10 minutes apart. In contrast the lower panel shows two days of data from Lilydale station in November 2009 when a smoke cloud was seen to move from west to east across the
north-east Tasmanian BLANkET stations. In this case the graph is much smoother.
A plot comparing signatures of smoke from local and remote sources, from PM2.5 data collected at the Lilydale BLANkET station in July (top) and November(lower) 2009.
On the reports page you can find an analysis of the November 2009 smoke event which was detected at the air stations in the Tamar Valley as well as across the north-east of the State - see BLANkET Technical Report 6. The source appears to have been a 20 ha bushfire near Barrington in central northern Tasmania.
There are now a number of other reports on the BLANkET report page on smoke impacts from planned burns.
What will be the value of the data? (Or: Why are you spending money measuring smoke in my area when I can tell when it is smoky every time I breath?)
BLANkET is providing broad-scale comprehensive data on smoke movement and dispersal in Tasmania. At the end of the autumn burning seasons a full analysis of the dataset is to be undertaken to assist with understanding these issues. The data and findings will be used to inform and refine smoke management practices.
The network is also providing valuable information on winter-time smoke concentrations in towns and communities resulting from domestic woodheater emissions.
Please see the BLANkET report page for details of these studies.