The DELTA Group

for the Detection and Evaluation of the Long-Range Transport of Aerosols

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Department of Applied Science



Size and Time Resolved Anthropogenic Components of Aerosols via Synchrotron X-Ray Fluorescence: Application to Asian Aerosol Transport

Thomas A. Cahill, Steven S. Cliff, Kevin D. Perry, Michael Jimenez-Cruz
University of California, Davis

and Scott A. McHugo

Advanced Light Source, Lawrence Berkeley National Laboratory



  • Aerosols have important climate implications, for instance by cooling the Earth on the order of as much as CO2 heats it.
  • Any single measurement of atmospheric properties is almost useless due to strong diurnal, synoptic, seasonal, and annual cycles.
  • Aerosols are the major uncertainty associated with global climate models.
  • "Climate Change and Greenhouse Gases," EOS Trans. V.80, #29 Sept 28, 1999, summarizes the peer reviewed literature that underlies the AGU’s position statement, Dec. 1998: Computer modeling of atmospheric aerosols on a global scale requires simplifications and assumptions so gross as to make any meaningful predicative successes "fortuitous."
  • Without measurement of the size, shape, and composition of aerosols, their source, transformation, transport and impacts cannot be unambiguously determined.
  • Simultaneous measurement of aerosol size, time and composition requires collection of particles onto a substrate, However, one can collect only a few mono-layers of particles before sizing is skewed by transfer to smaller stages due to particle-on-particle bounce.

Therefore, accurate and sensitive sampling and analytical techniques MUST be developed to allow detailed size and time resolved aerosol composition at many sites simultaneously.

The combination of innovative sampling and ex-post facto analysis using PIXE, synchrotron XRF, and Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (LDITOF-MS) allows us to reduce uncertainty associated with atmospheric aerosols.

Aerosol Analysis Techniques

  • PIXE (Proton Induced X-Ray Emission)—Quantitative elemental composition from Na through Fe.
  • PESA (Proton Elastic Scattering Analysis)—Quantitative H in vacuum (from organics).
  • s-XRF (Synchrotron Source X-Ray Fluorescence)—(Currently) Semi-quantitative ultra-high sensitivity elemental composition from (potentially) Na through Pb.
  • Beta-gauge mass, Beta-particles (e-) are attenuated through sample allowing size and time resolved aerosol mass measurement.
  • LDI-TOF/MS (Laser Desorption/Ionization-Time-of-Flight Mass Spectrometry)—Qualitative (at present) characterization of organic aerosols for large mass range. Matched time resolution to PIXE/PESA/XRF techniques.

Advanced Light Source - LBNL

  • Focused polarized white or tunable mono-energetic beam with high photon flux.
  • Typical analysis conducted with 12.5KeV beam with greater than 1012 photons/second flux.
  • Beam-spot variable from 250 x 250 mm to 2 x 2 mm.
  • Current configuration allows semi-quantitative elemental analysis from Si through Hg.
  • Future protocols will allow elemental analysis down to Na with full quantification of all detected elements to picogram quantities. This translates to ng/m3 elemental composition of ambient aerosols in a time resolution of minutes.

Sampler Technology

bullet Ex post facto analysis concept: Collect ambient samples continuously and analyze only those samples that are scientifically interesting based upon set criteria (Beta-gauge mass, other instrumental data, etc.)
bullet Couple new technology for continuous sampling with well established techniques using integrated filter sampling (DELTA-IAS).
bullet Ex post facto analysis allows small, relatively inexpensive, lightweight samplers do be field deployed, when coupled with high sensitivity technically advanced laboratory analyses.
bullet Ex post facto analysis allows future determination of time resolution from ambient samples: From 24-hours to 1 minute.
bullet Parallel substrates used in same sampler to optimize analysis techniques.
  • Greased Mylar—PIXE/XRF, major and trace elements
  • Teflon—PESA, H from organics
  • Al foil—LDI-TOFMS, organic speciation


  • Reduction of uncertainty associated with aerosol source, composition, transformation and transport is possible!
  • Highly time resolved size segregated analysis of aerosols is accomplished using impactor samplers and matched analytical techniques (PIXE, s-XRF, Beta-Gauge mass, LDI-TOF/MS).
  • Use of s-XRF (ALS Beamline 10.3.1) allows better, faster, cheaper sampling technology using continuous sampling regime and ex post facto analysis criteria.
  • Further refinement of ALS s-XRF to include lighter elements, higher sensitivity, and full quantification of elemental composition of aerosol samples is near.
  • High elemental sensitivity (to picogram quantities) and high time resolution (to 1 minute) make s-XRF an unsurpassed aerosol analytical technique.
  • Using new sampling and analytical techniques, such as the s-XRF at ALS Beamline 10.3.1 has aided identification of anthropogenic Asian aerosols in the United States mainland!


The DELTA group, the ALS-CXRO staff, and the CNL staff are gratefully acknowledged for their assistance.

Temporal Resolution

We use a continuous sampling protocol and ex post facto analysis with the time resolution set by the larger of either:

  1. the size of the sample "footprint" (ca. 250 mm), or
  2. the size of the analytical probe "footprint" (as small as 2x2 mm for s-XRF) 

Temporal Resolution

Analytical Technique

Probe "footprint"


Protons, 4.5 MeV;

soft beta particles

PIXE (Na – Pb); PESA (H);

Mass (gravimetric/beta gauge)

2 mm


Protons, 4.5 MeV PIXE (Na – Pb); PESA (H)

500 mm


Light (visible); 12 KeV/White x-rays;

Laser light (UV)

Optical absorption/scattering;

s-XRF (Si – Pb; high sensitivity for trace elements);


250 mm


12 KeV/White x-rays. s-XRF (Si – Pb; high sensitivity for trace elements)

80 mm

Duration of Sampling

Temporal Resolution








(Mass, PIXE, PESA)

(Mass, PIXE, PESA)

(s-XRF, optical, LDI-TOF/MS)

(s-XRF, optical)


1 month (28 days)

8 hour


1 hour

20 min

0.1 ng/m3

3 weeks

6 hour

90 min

45 min

15 min

0.15 ng/m3

2 weeks

4 hour

1 hour

30 min

7 min

0.2 ng/m3

1 week

2 hour

30 min

15 min

5 min

0.4 ng/m3

½ week (84 hour)

1 hour

15 min

8 min

3 min

0.8 ng/m3

¼ week (42 hour)

30 min

8 min

4 min

80 sec

1.6 ng/m3

1 day (30 hours)

21 min

6 min

2.5 min

50 sec

2 ng/m3

Standard and High Resolutions are routinely utilized

Example use of Techniques

Asian Aerosol Samples

  • Background: We and others have routinely observed Asian dust at Mauna Loa each Spring (1978 to present). Recently, Asian anthropogenic aerosols have been reported at MLO (Perry et al., 1999).
    • From these data (Perry et al., 1999) it is concluded that as much as 40% of the annual CO2 variability derives from mainland Chinese pollution.

Does this result extend to other sites and times?

bullet Experiment: A continuous aerosol sampling device (3 DRUM) was placed at the well instrumented UW Cheeka Peak Observatory in Spring 1998. Simultaneously, the IMPROVE aerosol network operated across the western US (Wed./Sat. 24-hr average filters).
bullet Result: A massive dust storm was recorded over the western US from April, 29—May, 3, 1999 as seen visually in the sky. Satellite data showed a source in central China and Mongolia. The dust episode impacted the Cheeka Peak site for ca. 60 hrs., and aerosols were sampled with high size and time resolution. PIXE analysis revealed H (from organic matter), and elements from Na through Fe, but no uniquely industrial signature found at MLO.
bullet HOWEVER: s-XRF analysis of these samples at the ALS was able to show:
bullet The presence of Asian (Manchurian) industrial aerosols.
bullet That the industrial aerosols arrived before the dust, and continued after the dust had subsided.
bullet That the size of the dusts were optically efficient.