The University of California, Davis

**[The UCD δ (DELTA]{.smallcaps}**[^1] **[) Group
IMPROVE-Equivalent]{.smallcaps}**

**[International Aerosol Sampler (δ-IAS)]{.smallcaps}**

Thomas A. Cahill, Kevin D. Perry, and Dabrina D Dutcher

δ-Group, Crocker Nuclear Laboratory, University of California,

One Shields Avenue, Davis, CA 95616

\(530\) 752-1120; tacahill@ucdavis.edu

Design Goals:

The δ (DELTA) Group has designed and built a sampler for aerosols
smaller than 2.5 μm in diameter (PM~2.5~) that addresses the following
goals:

1.  Aerosols are collected so as to result in maximum accuracy and
    precision of data representing both gross and trace species,

2.  Aerosols are collected in multiple filters so that standard
    analytical methods can achieve quantitative mass closure
    (gravimetric mass = sum of species),

3.  Aerosols are collected in accord with standard international
    protocols in particle size (ambient, PM~2.5~) and sampling duration
    (24 hr.) to maximize inter- comparability with prior and current
    global aerosol data.

Desirable factors include a sampler that is small, easily transportable,
inexpensive, rugged, able to stand weather, uses little power, easily
convertible for different voltages and frequencies.

Execution:

The δ Group international aerosol sampler (δ-IAS) was based upon the
California Air and Industrial Hygiene Laboratory's 23 l/min cyclone ^1^.
This device has become something of a standard 2.5 μm cut point cyclone
due to its clean cut point behavior and lack of tails for particles much
larger and much smaller than 2.5 μm in diameter. It was adopted by UC
Davis for the heart of the 76 site IMPROVE network^2^ after side by side
tests with many other samplers ^3,4^ . It was recommended by the UN's
WMO Global Atmospheric Watch panel on Quality Assurance of GAW data
(1993) and for GAW's Middle Eastern Network (1994-1998) and has been
adopted by many other groups ^5^. In November, 1996, (Federal Register)
the US Environmental Protection Agency deemed IMPROVE the standard for
all non-urban US sites. At this point, roughly 300 such cyclones are in
active use with another 225 on order for emplacement in the US, Spring,
1999.

In the IMPROVE^2^ configuration, there are three 2.5 μm channels, each
leading to a selected filter medium designed to optimize analysis:

Channel Denuder Filter Analyses

A none 25 mm Teflon Mass (gravimetric)

PIXE/XRF/PESA^6,7^

optical absorption^8^

B Carbonate 25 mm Nylon Ion chromatography

SO~4~^=^ , NO~3~^-^, NO~2~^-^, Cl^-^

C none 25 mm quartz Carbon by Combustion

OC (4 temps), EC (3 temps)

IMPROVE also has a channel for 10 μm particles.

The key concept adopted by IMPROVE (and the UN) is "integral
redundancy", in which there are enough redundant measurements to
establish both the precision and accuracy of the data. Examples include:

1.  Air flow is set by a critical orifice, confirmed by a vacuum gauge,
    and validated by non-critical orifice low pressure measurements
    (NIST traceable) across the cyclone,

2.  Mass (gravimetric) must equal the sum of all species,

3.  Sulfur\...Iron (by PIXE) equals Sulfur\... Iron (by XRF),

4.  Sulfate (by IC, Channel B) must equal 3 times sulfur (by XRF/PIXE),

5.  Organic Carbon (by carbon combustion) equals organic carbon (derived
    from hydrogen via PESA),

This protocol has been used by IMPROVE since 1988, resulting in, for
example, almost 60,000 of these comparisons. While the vast number agree
with extreme precision (r^2^ = 0.99+, sulfur versus sulfate), the
deviations give new information on chemical states, water bound to
aerosols, and other effects associated with certain regions and certain
seasons.

In recent years, measurements have shown that the IMPROVE sampler
matches many other PM~2.5~ samplers with high precision (errors \< 10%)
including the widely used virtual impactor^3^, the stacked filter
unit^4,9^ as well as high volume cyclone units previously tested in
field inter comparisons ^10^. For certain species (sulfates, soil,
\...), this has now been extended to physical impactor samples^11^ where
the shape of the cut point is not critical.

δ Group Configuration, International Aerosol Sampler (δ-IAS)

For the δ-IAS, the four standard pots of the IMPROVE sampler, usually
used for sequential Wednesday-Saturday sampling, are now used for the
Channel A (Teflon), Channel B (Nylon) and Channel C (quartz, tandem) 25
mm filters. A carbonate denuder is used in the inlet to remove nitric
acid and other acidic gasses, SO~2~, and NO~2~. The flow for each is
reduced to 7.7 l/min by critical orifices, checked by a vacuum gauge on
the pump, and validated by total flow measured by the pressure drop
across the cyclone. This results in the same 2.5 μm cut point as IMPROVE
and the ability to operate in three times higher mass concentrations
than IMPROVE without clogging the filter. The cost is that sensitivity
is reduced by a factor of 3.

One great advantage of the δ-IAS configuration over standard IMPROVE is
that the total units is only 18 x 30 x 44 cm in size, easily shipped by
overnight air carrier. Further, all three channels are supported by a
single pump, a 1/3 hp (roughly 250 watt) GAST double piston pump,
available in either 110v or 220 v models.

While the δ-IAS mirrors normal IMPROVE operational protocols in many
regards, we plan to do addition measurements from the three primary
ports to get better sensitivity and additional information especially
during extraordinary events and special studies. High priority
additional analyses include synchrotron-XRF on Channel A, (better
sensitivity than IMPROVE for trace metals), both anions and cations in
Channel B (IMPROVE does only anions) and GC/MS speciation on Channel C
(IMPROVE does only combustion). The δ-IAS is also flexible enough to
allow additional measurements via the fourth port. One such measurement
uses a low flow rate (0.1 l/min?) onto a Nuclepore filter. In most
circumstances, this allows for microscopic examination of single
particles to get shape and morphology.

Costs:

The units are at present made in the machine shops of the Crocker
Nuclear Laboratory, University of California, Davis, at actual cost. The
total cost of the system (before shipping to site) is roughly \$1250.
(including a \$350. pump). In addition, there need to be a number of
filter cassettes. If the cassettes are loaded and unloaded at the site,
and are bought new, the cost for 6 is \$120. However, surplus cassettes
may be available at nominal cost as IMPROVE is moving to a different
system. The samplers normally take about two to three months to order
and construct.

References:

1.  John, W, Wall, S.M., Ondo, J.L., *Atmospheric Environment*
    22:1627-1635 (1988).

2\. Malm, W.C., Sisler, J.F., Huffman, D., Eldred, R.A. and Cahill, T.A.
Spatial and seasonal trends in particle concentration and optical
extinction in the United States. *Journal of Geophysical Research,* Vol.
99, No. D1, 1347-1370 (1994).

3\. Hering, Susanne V., Bruce R. Appel, W. Cheng, F. Salaymeh, Steven H.
Cadle, Patricia A. Mulawa, Thomas A. Cahill, Robert A. Eldred, Marcelle
Surovik, Dennis Fitz, James E. Howes, Kenneth T. Knapp, Leonard
Stockburger, Barbara J. Turpin, James J. Huntzicker, Xin-Qui Zhang, and
Peter H. McMurry. Comparison of sampling methods for carbonaceous
aerosols in ambient air. *Aerosol Science and Technology.* 12:200-213
(1990).

4\. Cahill, Thomas A., Marcelle Surovik, and Ian Wittmeyer. Visibility
and aerosols during the 1986 carbonaceous species methods comparison
study. *Aerosol Science and Technology.* 12:149-160 (1990).

5\. Cahill, Thomas A. The international fine aerosol networks. *Nuclear
Instruments and Methods in Physics Research*. B75, pp. 217-221 (1993).

6\. Cahill, Thomas A. Compositional Analysis of Atmospheric Aerosols.
*Particle-Induced X-Ray Emission Spectrometry*, Edited by Sven A. E.
Johansson, John L. Campbell, and Klas G. Malmqvist. *Chemical Analysis
Series,* Vol. 133, pp. 237-311. John Wiley & Sons, Inc.

7\. Cahill, Thomas A. and Paul Wakabayashi. Compositional analysis of
size-segregated aerosol samples. Chapter in the ACS book *Measurement
Challenges in Atmospheric Chemistry*. Leonard Newman, Editor. Chapter 7,
pp. 211-228 (1993).

8.  Campbell, Dave, Scott Copeland, and Thomas Cahill. Measurement of
    aerosol absorption coefficient from teflon filters using integrating
    plate and integrating sphere techniques. *Aerosol Science &
    Technology*, 22:287-292 (1995).

> \*Campbell, David, S. Copeland, and T. Cahill. Comment on "Measurement
> of Aerosol Absorption Coefficient from Teflon using the Integrating
> Plate and Integrating Sphere Techniques". *Aerosol Science and
> Technology* 24:221-224 (1996).
>
> \*Campbell, Dave, and Thomas Cahill. Addendum to Response. *Aerosol
> Science and Technology* 24:290 (1996).

9\. Cahill, Thomas A., Robert A. Eldred, Patrick J. Feeney, Peter J.
Beveridge, and L. Kent Wilkinson. The stacked filter unit revisited. In
*Visibility and Fine Particles.* C.V. Mathai, Editor. pp. 213-222
(1990).

10\. Mathai, C.V., John G. Watson, Jr., C. Fred Rogers, Judith C. Chow,
Ivar Tombach, Judith O. Zwicker, Thomas Cahill, Patrick Feeney, Robert
Eldred, Marc Pitchford, and Peter K. Mueller. Intercomparison of ambient
aerosol samplers used in western visibility and air quality studies.
*Environmental Science & Technology.* Vol. 24, No. 7, pp. 1090-1099
(1990).

11\. T.A. Cahill, P, Wakabayashi, T. James. Chemical State of Sulfate at
Shenandoah National Park During Summer, 1991. *Nuclear Instruments and
Methods in Physics Research B: Beam Interactions with Materials and
Atoms,* 109/110, 542-547 (1996)*.*

[^1]: ^\*^ Determination of Extinction and Long-range Transport of
    Aerosols