A new approach to the combination of IBA techniques and wind back trajectory data to determine source contributions to long range transport of fine particle air pollution
David D. Cohen
⇑, Jagoda Crawford, Eduard Stelcer, Armand Atanacio
Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia
a r t i c l e i n f o
Article history:
Available online 26 July 2011 Keywords:
IBA techniques PIXE Fine particles Long range transport
a b s t r a c t
A new approach to link HYSPLIT back trajectories to the source of fine particle pollution as characterised by standard IBA techniques is discussed. The example of the long range transport of desert dust from inland Australia across the eastern coast is used to show that over a 10-year period extreme soil events originated from major agricultural regions some 30% of the time and that dust from known deserts are not always the problem.
Crown CopyrightÓ2011 Published by Elsevier B.V. All rights reserved.
1. Introduction
The simultaneous application of PIXE, PIGE, RBS and PESA tech- niques for multi-elemental characterisation of fine particle air pol- lution is now well established[1–3]. These IBA techniques provide elemental concentrations for H to Pb with sensitivities down to 1 ng/m3of air sampled on standard air particulate filters. This en- ables the determination of source fingerprints containing up to 20 different elemental species as well as estimates of their contribu- tions to the total gravimetric mass on the filters[3]. Recently this work has been extended to include wind speed and direction data enabling source locations to be accurately determined and long range transport of air pollution to be followed over several years [3,4].
This paper discusses a new approach of combining IBA data with long term hourly wind back trajectory data from the receptor site to identify real source regions hundreds of kilometres away.
Unlike previous approaches this method links the trajectories using HYSPLIT[5]and the source fingerprints[4,6]to source re- gions by counting up the number of back trajectories that originate from the sampling site and also intersect these source regions. This approach enables quantitative estimates, over several years, of the contributions of these source regions to the fingerprints measured by IBA techniques at the receptor or sampling site. To demonstrate the application of this new method we discuss below in detail the long range transport of dust from Australian deserts over hundreds
of kilometres across the east coast of Australia between 2001 and 2010.
2. Method
The four simultaneous IBA techniques of PIXE, PIGE, RBS and PESA were used to obtain elemental concentrations (ng/cm2) for the 24 elements: H, C, N, O, F, Na, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br and Pb on stretched Teflon filers. These techniques have been described extensively in detail previously [1,2and references therein]. In summary, 2.6 MeV proton beams of around 10 nA for a total charge collection of 3
l
C and beam diameters of 8 mm were used to irradiated each Teflon filter which was exposed for 24 h at a flow rate of 22 l/min during the study period. PIXE provided information on elements from Al to Pb, PIGE on F, Na and Al, RBS on C, N and O and PESA on the H concentra- tions. Typical spectra for such IBA analyses have been published (Ref.[1]).In particular here we used five of these elements, Al, Si, Ca, Ti and Fe, to define the fine soil content in the standard way[7]by assuming they occurred in their oxide forms and summing the oxide contribu- tions for these five elements. That is, the fine soil component was de- fined as, [Soil] = 2.20[Al] + 2.49[Si] + 1.63[Ca] + 1.94[Ti] + 2.42[Fe], where the terms in square brackets represent the elemental concen- trations in (
l
g/m3) of air sampled and the constants associated with each elemental reflect their common oxide forms.Filters containing fine PM2.5 particles were collected every Sun- day and Wednesday between 1 January 2001 and 31 December 2010 at a rural/urban site at Muswellbrook at 32.26°S, 150.89°E some 250 km NW of Sydney, Australia.Fig. 1shows this fine soil 0168-583X/$ - see front matter Crown CopyrightÓ2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.nimb.2011.07.071
⇑Corresponding author.
E-mail address:[email protected](D.D. Cohen).
Nuclear Instruments and Methods in Physics Research B 273 (2012) 186–188
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concentration measured at the Muswellbrook site between 2001 and 2010. The average soil concentration was 0.37 ± 3.2
l
g/m3, being on average about 9% of the total fine mass. Sampling days with soil concentrations above 1.3l
g/m3were defined as extreme events (see horizontal line inFig. 1). There were 43 days from 961 sampling days between January 2001 and December 2010 with soil concentrations greater than 1.3l
g/m3. The question now posed is what was the origin of the soil associated with these extreme events?To answer this question we used the HYSPLIT program[5]to plot hourly back trajectories for each of the extreme days.Fig. 2 contains such a collection of 24-hourly 7-day back trajectories for the 23 November 2008 extreme event shown inFig. 1. It shows back trajectories leaving the Muswellbrook sampling site at heights of 300 and 500 m above ground level and travelling to the west and south and out into the southern ocean off Australia.
The 15 rectangular boxes drawn inFig. 2show the known desert areas and schematically represent their extent within the Australian continent. The trajectories for 23 November 2008 event intersect with boxes 1 and 15 but not many others. As this approach demon- strates it is a tedious and somewhat messy process to perform daily back trajectories for all the extreme event days between 2001 and 2010. To improve the process we have developed a FORTRAN code to plot all hourly back trajectories over 10 years and their intersec- tions with all the 15 boxes drawn inFig. 2. To test that these trajec- tories cover all boxes and our region of interest we plot the number of such intersections for every 1°1°cell in the region of interest, which is shown inFig. 2for 7-day back trajectories. Clearly these cover the region of interest well with at least more than 5 intersec- tions per cell and cells within a 500-km radius of the sampling site having more than 5000 intersections per cell. The longitude and atitude range covers some 4000 individual 1°1°cells between 110–160°longitude and 50°to 10°latitude with an average num- ber of non-zero intersections per cell of 1606 and a median value of 853 intersections per cell. In most cases the desert regions depicted inFig. 2are more than ± 1°or ± 100 km across. The size of the desert boxes and the time along back trajectories within HYSPLIT is most important and is related to the typical wind speeds along a trajec- tory. A detailed examination of the HYSPLIT data showed that there were no wind speeds in excess of 100 km/h. Hence hourly points along each 7-day back trajectory are more than sufficient and no hourly points will miss any desert boxes with dimensions greater than ± 100 km from the box centre or 200 km across.
3. Results
Every time one of these back trajectories traverses a desert box we place a dot in that box as shown inFig. 3. The number of dots per box is then a quantitative measure of the relative impact that each of these desert regions has on the sampling site hundreds of kilometres away.
Table 1summarises the number of intersections per desert re- gion (boxes 1–15) for all 43 extreme event days with soil > 1.3
l
g/m3. More than 65% of all extreme events came from only two regions, namely, Lake Mungo (1) and the Riverina (15).Other major desert dust sources had relatively minor impact on the Muswellbrook site. The Riverina area is not a desert area it is actually a major agricultural area used to grow crops to feed the Sydney region. This is a significant finding not previously reported.
0 1 2 3 4 5 6 7 8 9 10
3/01/2001 3/07/2001 3/01/2002 3/07/2002 3/01/2003 3/07/2003 3/01/2004 3/07/2004 3/01/2005 3/07/2005 3/01/2006 3/07/2006 3/01/2007 3/07/2007 3/01/2008 3/07/2008 3/01/2009 3/07/2009 3/01/2010 3/07/2010 Soil (µg/m3 )
Muswellbrook Soil 2001-2010
23-Nov-08
Fig. 1.Plot of the PM2.5 soil concentrations at the Muswellbrook site between January 2001 and December 2010.
-50 -45 -40 -35 -30 -25 -20 -15 -10
110 115 120 125 130 135 140 145 150 155 160
Latitude
Longitude
7 Day Back Trajectories Muswellbrook 300m, 500m
23-Nov-08 Cities Sites >5,000
>100 >5
Brisbane
Sydney Darwin
Hobart Adelaide
Broome
Heron Is.
Perth 1
2 3 5 4
6 7
8 9
10 11
12
13 14
15
Fig. 2.A plot of the number of 7-day back trajectory intersections per 1°1°cell originating from the Muswellbrook sampling site on the Australian east coast for every hour of every sampling day between January 2001 and October 2010. Greater than 5000 intersections per cell are (), between 5000 and 100 intersections (s) and between 100 and 5 intersections are (+). Also shown are 24 typical hourly back trajectories for the 23 November 2008 a high soil day at Muswellbrook site.
1 3 2 5 4
6 7
8 10 9
11 12
13 14
15
-50 -45 -40 -35 -30 -25 -20 -15 -10
110 115 120 125 130 135 140 145 150 155 160
Latitude
Longitude
Cities Sites 300m 500m Dust
Darwin
Brisbane Heron Is
Hobart Adelaide
Broome
Muswellbrook Perth
Sydney
Cape Grim
Fig. 3.Plot of 7-day back trajectories every hour with intersections per desert region plotted as red squares for 300 m starting height and blue diamonds for 500 m starting height from the Muswellbrook sampling site (large dot) on the east coast of Australia north of Sydney. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.).
D.D. Cohen et al. / Nuclear Instruments and Methods in Physics Research B 273 (2012) 186–188 187
4. Summary
We have applied HYSPLIT back trajectories and IBA techniques to determine fine particle soil concentrations measured over a 10-year period and to identify possible source regions. These re- gions were previously considered to be the desert regions of Australia up to 2000 km west of the sampling site. By linking
trajectories to sources and receptor site we have quantitatively determined which desert regions were most likely to contribute to extreme soil events at the sampling site. The surprising result was that agricultural activities more than 500 km from the sam- pling site seemed to contribute to high fine soil events much more than soil from desert regions as previously thought. This new ap- proach to source identification is currently being applied to finger- prints, obtained by IBA methods, from coal fired power stations in Australia and in Asia to identify major polluters and their relative contributions to ambient air pollution.
Acknowledgements
The NOAA Air Resources Laboratory (ARL) made available the HYSPLIT transport and dispersion model and the relevant input files for generation of back trajectories used in this paper. We would like to acknowledge the help of the accelerator staff at ANSTO and the financial support of Muswellbrook Council for help with fine particle sampling and IBA support throughout this work.
References
[1] D.D. Cohen, Nucl. Instr. and Meth. B136 (138) (1998) 14.
[2] D.D. Cohen, E. Stelcer, O. Hawas, D. Garton, Nucl. Instr and Meth. B219 (220) (2004) 145–152.
[3] D.D. Cohen, J. Crawford, E. Stelcer, V.T. Bac, Atmos. Environ. 44 (2010) 320–328.
[4] D.D. Cohen, E. Stelcer, D. Garton, J. Crawford, Aerosol pollution research 2 (2011) 182–189.
[5] R.R. Draxler, G.D Rolph, HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) Model access via NOAA ARL READY, NOAA Air Resources Laboratory, Silver Spring, MD, 2003. Available at:www.arl.noaa.gov/ready/hysplit4.html.
[6] P. Paatero, U. Tapper, Environmetrics 5 (1994) 111–126.
[7] W.C. Malm, J.F. Sisler, D. Huffman, R.A. Eldred, T.A. Cahill, J. Geophys. Res. 99 (1994) 1347–1370.
Table 1
The number of intersections in each of the desert boxes shown inFig. 3for the extreme soil events at the Muswellbrook site.
Soil > 1.3lg/m3 300 m 500 m
Region Soil
inter.
% Soil inter.
Soil inter.
% Soil inter.
(1) Lake Mungo 391 33.0 382 36.5
(2) Lake Windaunka 106 8.9 103 9.8
(3) East Flinders 68 5.7 56 5.3
(4) Olympic Dam 81 6.8 60 5.7
(5) Emu Fields Salt 25 2.1 17 1.6
(6) Lake Eyre North 40 3.4 35 3.3
(7) Simpson Desert 12 1.0 11 1.1
(8) Great Victorian West 16 1.4 9 0.9
(9) Great Victorian East 30 2.5 28 2.7
(10) Gibson Desert 10 0.8 11 1.1
(11) Little Sandy Desert 4 0.3 6 0.6
(12) Great Sandy Desert West
8 0.7 4 0.4
(13) Great Sandy Desert East
8 0.7 1 0.1
(14) Tanami Desert 5 0.4 7 0.7
(15) Riverina Agricultural 381 32.2 317 30.3
Total with soil > 1.3lg/m3
1185 1047
% of all intersections 10.5 9.3
188 D.D. Cohen et al. / Nuclear Instruments and Methods in Physics Research B 273 (2012) 186–188