BLANkET1 Brief Report 7

Smoke from a bushfire at Ansons Bay, north–eastTasmania moving into to the Tamar Valley,

23rd January 2010

Air Section, EPA Division, February 2011

1 Summary

Smoke from a bushfire at Ansons Bay, north–east Tasmania, on the 23rd ofJanuary 2010 moved westwards towards the Tamar River. The BLANkET airstations at Derby, Scottsdale and Lilydale each detected the smoke as it moved.Ti Tree Bend station(Launceston) and the Rowella station in the lower Tamaralso detected the smoke. Derby is approximately 35 km from the fire location,while Ti Tree Bend and the Rowella stations are approximately 100 km fromthe burn. The peak 10–minute PM2.5 concentrations at these stations were oforder 10 to 15 µg m−3. These data are interesting in that there was little, if any,decrease in measured smoke concentration at Derby, Scottsdale, Lilydale, andRowella stations, even though Rowella (100 km from the Ansons Bay fire) isabout three times further away from the source than is Derby (∼35 km range).

1.1 Air quality data

PM2.5 and meteorological data for the BLANkET stations of Derby, Scottsdaleand Lilydale, and the major air stations at Ti Tree Bend (Launceston) andRowella lower Tamar valley), for the 23rd of January 2010 are shown in Fig-ures 1, 2, 3, 4 and 5 respectively. All three BLANkET stations show an intervalof mildly elevated PM2.5 data during the afternoon 2. At these stations thetime of smoke onset during the afternoon is preceded by a wind change froma southerly or south–south–westerly to a north or north–east wind. In pass-ing, it is worth noting the step–wise increases in relative humidity seen in theBLANkET station data at these times, and then again at smoke onset shortlyafterwards. This is the signature of a more humid air mass moving in with thewind change.

The PM2.5 values at all three stations were in the range of 10 to 15 µg m−3

during the interval of smoke. At Launceston there is a small but marked eleva-tion in PM2.5 near 19:30 AEST. At Rowella the hourly–averaged PM2.5 reached

1Base–Line Air Network of EPA Tasmania2Additionally Derby shows elevated PM2.5 values for several hours from midnight. The

cause of this is still under study.

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to near 20 µg m−3 near 21:00 AEST. Rowella PM2.5 data are obtained witha TEOM3. Missing data in Figure 5 are related to instrumental performance.The TEOM PM2.5 instrument has only been relatively recently used for PM2.5

measurement in Tasmania. Early data suggest a potential for slightly overesti-mating the PM2.5 value under certain conditions, but this has not been firmlyestablished as a regular occurrence.

Figure 1: Derby BLANkET station data, 23rd January 2010. Top panel: PM2.5

data. Lower panel: Meteorological data. The smoke measured at Derby earlyon the 23rd of January is of unknown origin.

3Tapered Element Oscillating Microbalance

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Figure 2: Scottsdale BLANkET station data, 23rd January 2010. Top panel:PM2.5 data. Lower panel: Meteorological data.

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Figure 3: Lilydale BLANkET station data, 23rd January 2010. Top panel:PM2.5 data. Lower panel: Meteorological data.

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Figure 4: Ti Tree Bend, 23rd January 2010, PM2.5 data.

1.2 Satellite Image

The MODIS Aqua image for north–eastern Tasmania for the afternoon of the23rd of January 2010 is shown in Figure 6. An inferred fire location in thefar north–east of the state, derived by the NASA Rapid Response program, isindicated by a red polygon. There is an appearance of a faint plume of smokewhich can be traced to the south–westward. Air stations are indicated by thered ‘balloon’ symbols. The stations most of interest for this study are: DE =Derby; SC = Scottsdale; LD = Lilydale; RO = Rowella.

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Figure 5: Rowella air station data, 23rd January 2010. PM10 and PM2.5 data.

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Figure 6: MODIS Aqua image for north–eastern Tasmania for the 23rd of Jan-uary 2010, from swaths taken at 13:20 and 15:00 AEST. An inferred fire locationin the far north–east of the state, derived by the NASA Rapid Response pro-gram, is indicated by a red polygon.

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Figure 7: Ansons Bay fire location (blue diamond), from the TFS webpages.

1.3 Inferred source

The derived fire location shown in Figure 6 corresponds to a wildfire at AnsonsBay, listed on the Tasmanian Fire Service (TFS) webpage on the 23rd of Jan-uary. This fire had burnt out 100 ha on 23rd January 2010, and had burnt atotal of 200 ha when reported as extinguished on the 26th. The location of thefire is shown as a blue diamond in Figure 7, obtained from the TFS website. Thefire was reported as an escaped permit burn. The permit burn was ignited onthe 22nd of January 2010. The local TFS brigade responded to the wildfire at14:00 EDT (13:00 AEST) on the 23rd. The wildfire burnt mainly in grassland.

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Station Range to Ansons Bay fire (km) Smoke onset (AEST)Derby 35 14:00Scottsdale 58 17:10Lilydale 83 18:40Ti Tree Bend 98 19:30Rowella 104 (20:00)

Table 1: Distances from the Ansons Bay fire to the northern Tasmania airstations, and smoke onset times at these stations in AEST.

2 Discussion

Figure 8 shows the PM2.5 time series for Rowella, Ti Tree Bend, Lilydale, Scotts-dale, and Derby stations for the 23rd of January 2010. The time of smoke arrivalat these stations is clearly in the order (earliest to latest): Derby, Scottsdale,Lilydale, and Rowella. Smoke onset does not necessarily mean the front ofthe plume reached the station. These air stations are approximately all in thesame direction when viewed from the site of the Ansons Bay fire, as is shownin Figure 9. An oblique ‘birds–eye–view’ view of the same region, using GoogleEarth, is shown in Figure 10. (Ti Tree Bend air station is obscured by the localtopography in this view.)

Table1 lists for each station the air–line distance to the Ansons Bay bushfire,and the estimated time of smoke onset at the station on the 23rd of January2010. For Rowella the onset time is very approximate, as the TEOM data usedare of 1–hour time–resolution.

Derby town (and air station) is located in a narrow valley at least 100 mbelow the surrounding landscape. It is noted that the wind speed and directionmeasured at Derby may not necessarily be representative of the wind speedmeasured away from the valley. The wind speeds measured at Scottsdale andLilydale during the smoke interval were around 15 to 20 km hr−1, in an east tonorth–easterly direction. Taking this as a guide, and assuming a mean speedof 17 km hr−1, the smoke transit–time from the Ansons Bay bushfire locationto the stations listed in table 1 can be calculated. Using this wind speed, theknown station distances to the fire, and the observed onset times, a time of‘departure’ for the smoke leaving the fire can be calculated. These are shown inTable 2. The smoke departure times are all near 13:40 AEST, except for Derby.This is consistent with the suggestion that the Ansons Bay bushfire was theorigin of the elevated smoke levels at these northern Tasmanian air stations.

The relative constancy of the maximum PM2.5 concentrations at Derby,Scottsdale, Lilydale, and to an extent also at Rowella, is of interest. A plumethat laterally disperses as it travels away from the source would be expectedto result in decreasing concentrations with increasing range from the fire. Thenear–constant concentrations imply, among other possibilities, either little lat-eral dispersion or that a combination of dispersion together with movement of

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Station Transit time at 17 km hr−1 Time of start (AEST)Derby 2 12:00Scottsdale 3.5 13:40Lilydale 5 13:40Ti Tree Bend 5.7 13:50Rowella 6 (14:00)

Table 2: Calculated smoke transit–times from Ansons Bay to the named station,assuming a 17 km hr−1 wind, and inferred start time of smoke leaving the firelocation.

the location of plume centre, relative to the stations, produced a nearly constantPM2.5 signal from Derby to the Tamar. It is not possible at present to decidewhich mechanism, if either, was dominant. Future measurements of other smokeplumes may provide useful information.

3 Acknowledgements

BLANkET stations are sited at properties owned or operated by Ben LomondWater, Break O’Day Council, Cradle Mountain Water, Dorset Council, ForestryTasmania Huon District, Huon Valley Council, and West Tamar Council.

The TFS is thanked for providing information from their incident database.MODIS images are from the NASA/Goddard Space Flight Center ‘MODISRapid Response’ web site4.

Report compiled by J. Innis.

4http://rapidfire.sci.gsfc.nasa.gov/

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Figure 8: Rowella, Ti Tree Bend (Launceston), Lilydale, Scottsdale, and DerbyPM2.5 data, 23rd January 2010. 11

Figure 9: A plan view of the five northern Tasmanian air stations at Derby(DE), Scottsdale (SC), Lilydale (LD), Rowella (RO), and Ti Tree Bend (TT),relative to the location of the 23rd January 2010 Ansons bay bushfire. GeorgeTown (GT), St Helens (SH) and Fingal (FI) air stations are also shown.

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Figure 10: A down-range view of the four northern Tasmanian air stations atDerby (DE), Scottsdale (SC), Lilydale (LD), and Rowella (RO), as seen fromnear the site of the 23rd January 2010 Ansons bay bushfire. Ti Tree Bend airstation is obscured by the local topography.

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4 Appendix –Frames from an animation of the23rd of January 2010 smoke in northern Tas-mania

Figure 11: A visualisation of air quality and wind data for northern Tasmania at11:00 AEST on the 23rd of January. Wind direction and speed at the BLANkETair stations are indicated by the arrow directions and lengths. PM2.5 levels areindicated by the size and colour of diamond–shaped symbols (see the latterframes) - at 11:00 AEST PM2.5 levels were very low. The approximate locationof the Ansons Bay bushfire is marked by the X. The air stations are labelled asfollows: GT: George Town; RO: Rowella; TT: Ti Tree Bend (Launceston); LD:Lilydale; SC: Scottsdale; DE: Derby; SH: St Helens; FI: Fingal.

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Figure 12: As for Figure 11, but for 13:00 AEST, 23rd January 2010. Smokelevels are still low across northern Tasmania. The wind at Derby has turned toa light north–easterly.

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Figure 13: As for Figure 11, but for 15:00 AEST, 23rd January 2010. Smokelevels are elevated at Derby.

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Figure 14: As for Figure 11, but for 17:00 AEST, 23rd January 2010. Smokelevels remain elevated at Derby. The wind at Scottsdale is turning to the north–east.

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Figure 15: As for Figure 11, but for 18:00 AEST, 23rd January 2010. Smokelevels have fallen at Derby but have increased at Scottsdale on the north–eastwind. The wind at Lilydale is westerly.

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Figure 16: As for Figure 11, but for 19:00 AEST, 23rd January 2010. Smokelevels remain elevated at Scottsdale and have increased at Lilydale. The windat Lilydale is north–easterly.

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Figure 17: As for Figure 11, but for 20:00 AEST, 23rd January 2010. Smokelevels have dropped at Scottsdale, remain high at Lilydale, and have increasedat Rowella and Ti Tree Bend.

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Figure 18: As for Figure 11, but for 21:00 AEST, 23rd January 2010. Smokelevels have dropped at Lilydale and at Ti Tree Bend, but have slightly increasedat Rowella.

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Figure 19: As for Figure 11, but for 22:00 AEST, 23rd January 2010. Smokelevels have dropped at Rowella. Ti Tree Bend remains slightly elevated.

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