Clean Air Status and Trends Network Annual Report: 2011 Page: 43 of 101
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CASTNET 2011 Annual Report
The Effect of Differences in Annular Denuder System and CASTNET Filter Pack
Concentration Data Relative to Estimates of Atmospheric Deposition
The primary purpose of the Ammonia CASTNET CSN Study (ACCS) was to conduct a Nr inter-
comparison study at five CASTNET sites for one year (Rogers et al., 2012). See the sidebar on
page 23 in Chapter 2 for a synopsis of ACCS.
While the primary purpose of ACCS was to evaluate NH3 samplers and their bias, one of the benefits
of ACCS was an increased understanding of how well the standard CASTNET filter pack performed
relative to ADS (EPA Modified Compendium Method 1.0. 4.2) in terms of estimating atmospheric
deposition of sulfur and nitrogen species.
Results from ACCS (Rogers et al., 2012) show that, in general, the current CASTNET filter packs
compared favorably with the ADS when measuring S02, total NO3, SO, and NH4. Both systems
consistently measured these standard CASTNET analytes. Total N03 measurements were slightly
higher for the CASTNET filter pack compared with the ADS because the CASTNET filter pack has an
open face while the ADS has a 2.5 micrometer size cut cyclone separator. The cyclone feature allows
coarse-sized N03 particles (e.g., sodium and calcium nitrate) to be removed prior to sampling by the
ADS. The filter pack samples are without size restriction, which results in the collection of both coarse
and fine particles.
Comparisons of sulfur species were consistently better than for nitrogen species. Figure 3a shows the
comparison for SO2 between the CASTNET filter pack and two ADS at the Arendtsville, PA (ARE128)
CASTNET site. The results between the two systems were very consistent. Similar results were also
found when comparing S04 concentrations. Sulfur species are not subject to the volatilization and
partitioning found with nitrogen species. In addition, particulate sulfur species are dominated by fine
particles, which are less affected by the size restriction imposed by the cyclone on the ADS. As a
consequence, estimates of deposition of sulfur species based on either the CASTNET filter pack or
the ADS data are similar.
Figure 3a Comparison between CASTNET Filter Pack and ADS SO2 Concentrations at the
ARE128, PA Site
12
ARE128 FP
10 iARE128ADSSC1
ARE128ADSSC2
MC
8
CM
C
6
"c4
- - ' 0) - ' 0 - - - -r -' ) '1 o r- co - ' 0) - ' 0
Note: FP = filter pack
ADSSC = sodium carbonate-impregnated ADSChapter 3: Atmospheric Deposition
38
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AMEC Environement & Infrastucture, Inc. Clean Air Status and Trends Network Annual Report: 2011, report, February 2013; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc949427/m1/43/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.