Annular denuders

Vapor (P° >0.1 Pa) Vapor-baerosols (P° 10 -0.1 Pa) Aerosols (P° < 10 Pa) Adsorbents, canisters, impingers Filters, adsorbents, annular denuder Filters, impactors, cyclone separators... 

Coutant, R. W., P. J. Callahan, M. R. Kuhlman, and R. G. Lewis, Design and Performance of a High-Volume Compound Annular Denuder, Atmos. Environ., 23, 2205-2211 (1989). 

Gundel, L. A., V. C. Lee, K. R. R. Mahanama, R. K. Stevens, and J. M. Daisey, Direct Determination of the Phase Distributions of Semi-Volatile Polycyclic Aromatic Hydrocarbons Using Annular Denuders, Atmos. Environ., 29, 1719-1733 (1995a). 

FIGURE 11.31 Comparison of gaseous HN03 measurements made simultaneously in Claremont, California, on two different days using FT-IR shown as with error bars and by a filter pack (FP), a difference denuder (DD), an annular denuder (AD), and tunable diode laser spectroscopy (TDLS) (adapted from Hering et al., 1988). 

Koutrakis, P., J. M. Wolfson, J. L. Slater, M. Brauer, J. D. Spengler, R. K. Stevens, and C. L. Stone, Evaluation of an Annular Denuder/Filter Pack System to Collect Acidic Aerosols and Gases, Environ. Sci. Technol., 22, 1463-1468 (1988). 

Langford, A. O., P. D. Goldan, and F. C. Fehsenfeld, A Molybdenum Oxide Annular Denuder System for Gas Phase Ambient Ammonia Measurements, J. Atmos. Chem., 8, 359-376 (1989). 

Williams, E. L II, and D. Grosjean, Removal of Atmospheric Oxidants with Annular Denuders, Environ. Sci. Technol., 24, 811-814 (1990). 

Figure 3. Schematic diagram of an annular denuder system. (Reproduced with permission from reference 22. Copyright 1990.)...

Design Parameters. With the assumption that the walls of the annulus are coated with a perfect collector for HN03, the efficiency of an annular denuder can be calculated (53) ... 

The measurement of FPN from the N03 recovered from a backup Teflon-nylon or nylon filter with the ADM is subject to some of the same potential sources of error as with the DDM. No loss of FPN passing through the annular denuder is expected on the basis of particle-loss measurements (55). Although HONO is efficiently removed ahead of the filter or filters, nearly all of the PAN would reach the nylon filter. Retention of PAN on nylon filters has been reported to be insignificant. Thus, relatively little error in FPN is expected with the ADM and CO -glycerol coated denuders. 

Uncertainty in Correcting Atmospheric Data. The level of uncertainty with this method can be illustrated with results from atmospheric trials (57). After 4- to 6-h samples were collected in Southern California with CO -glycerol coated annular denuders during a late fall period, the N03" recovered... 

The efficiency of HN03 collection with a single annular denuder should be confirmed by each user with a known source of HN03, regardless of denuder coating used. On the basis of laboratory studies, Ferm and Sjodin (42) reported a technique that can be used to correct simultaneously for penetration of HN03 through the first of tandem denuders as well as for artifact N03" due to atmospheric species retained with low efficiency. 

Because of the labor-intensive nature of annular denuder sampling, alternative techniques deserve further scrutiny. The DDM, relying on Teflon-nylon filter packs (or nylon filters alone) and an anodized aluminum annular denuder ahead of one of a pair of modified dichotomous samplers (46), merits evaluation for the influence of potential interferents (e.g., HONO). The DDM with NaCl-coated denuders would probably be nearly free of interference from HONO, but this conclusion requires evaluation. Because coarse particulate N03 must be excluded to achieve improved accuracy for HN03 and fine particulate N03, supplementary samplers are needed to obtain improved estimates of total as well as coarse particulate... 

Annular denuder Cyclone or impactor (Teflon) Same as with denuder Same as with filter pack method... 

When the inlet length is expressed in terms of number of gap widths , the difference between the flow in a tube and the flow in an annulus of narrow gap differs only by 25% [(0.05 - 0.04)/0.05]. This situation is an indication that the growth of the laminar boundary layers from the wall to the center of the channel is similar in both cases. Because duct friction coefficients, a measure of momentum transfer, do not vary by more than a factor of 2 for ducts of regular cross sections when expressed in terms of hydraulic diameters, the use of the inlet length for tubes or parallel plates can be expected to be a reasonable approximation for the inlet lengths of other cross sections under laminar flow conditions. In the annular denuder, the dimensionless inlet length for laminar flow development, L, can be expressed as... 

Direct determination of the phase distributions of semi-volatile polycyclic aromatic hydrocarbons using annular denuders. Atmospheric Environment, 29, 1719-33. 

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