Diffusion denuder

Eatough, D. J., D. A. Eatough, L. Lewis, and E. A. Lewis, Fine Particulate Chemical Composition and Light Extinction at Canyonlands National Park Using Organic Particulate Material Concentrations Obtained with a Multisystem, Multichannel Diffusion Denuder Sampler, J. Geophys. Res., 101, 19515-19531 (1996). 

However, in at least one intercomparison study using diffusion denuders and transition flow reactors, different results were obtained for some important atmospheric gases such as S02, HNO-, and H+, where the TFR values were about 30, 80, and 85% higher, respectively, than those from the denuder system (Sickles et al., 1989) the researchers attributed these differences to biases in the TFR measurements. 

Durham, J. L L. L. Spiller, and T. G. Ellestad, Nitric Acid-Nitrate Aerosol Measurements by a Diffusion Denuder A Performance Evaluation, Atmos. Environ., 21, 589-598 (1987). 

Febo, A., C. Perrino, and I. Allegrini, Measurement of Nitrous Acid in Milan, Italy, by DOAS and Diffusion Denuders, Atmos. Environ., 30, 3599-3609 (1996). 

Fox, D. L L. Stockburger, W. Weathers, C. W. Spicer, G. I. Mackay, H. I. Schiff, D. J. Eatough, F. Mortensen, L. D. Hansen, P. B. Shepson, T. E. Kleindienst, and E. O. Edney, Intercomparison of Nitric Acid Diffusion Denuder Methods with Tunable Diode Laser Absorption Spectroscopy, Atmos. Environ., 22, 575-585 (1988). 

Design Parameters. In a diffusion denuder an airstream, in laminar flow, contacts a surface (e.g., the inner wall of a tube) coated with a sorptive or reactive trapping medium for the gaseous pollutant of interest. Fine particles, which have diffusion coefficients more than 4 orders of magnitude smaller than those for gases, penetrate the denuder with high efficiency. Forrest et al. (40) reported losses of 0.2-2.2% for particles between 0.3 and 0.6 xm and about 4-5% for 1- to 2- xm particles. 

The theoretical efficiency of a diffusion denuder for a gaseous pollutant can be calculated for various geometries with the assumption of a high probability for reaction and complete retention of the pollutant upon contact... 

Diffusion Denuders for Specific Organic Compounds. Diffusion de-nuder techniques have been applied successfully to sampling individual organic materials, including pesticides (82), nicotine (83, 84), and PAH compounds (63). The methodology and results relating to PAH compounds are detailed here. 

Johnson, N. D. Evaluation of a Diffusion Denuder Based Gas/Particle Sampler for Chlorinated Organic Compounds, Presented at the 1986 EPA/APCA Symposium on Measurement of Toxic and Related Air Pollutants, Research Triangle Park, NC, 1986. 

Three reviews describing applications of diffusion denuders have been published. The doctoral dissertation of Ferm (31) reflects considerable experience with single-tube denuders for the measurement of a variety of species. The review by Ali et al. (32) is extensive it provides an excellent historical and theoretical background and summarizes the literature based on the type of analyte gas determined. The focus of the most recent review, by Cheng (19), is diffusion batteries used for size discrimination of aerosols as well as diffusion denuders. Various physical designs are discussed in some detail in that review. 

When the denuder active surface is an inert porous membrane such that the analyte molecule must diffuse across the pores to be trapped by an absorber liquid, only a fraction of the membrane surface is porous, and the pores may also be tortuous. Consequently, collision at the membrane surface is not synonymous with uptake. Corsi et al. (45) developed a numerical solution for the collection efficiency observed for such a membrane-based diffusion denuder, hereinafter referred to as a diffusion scrubber (DS). Both groups of researchers dealing with the issue of less than unity uptake probability reached the conclusion that this value must be very much less than... 

The existing systems can be broadly classified into two groups systems that deal with a gaseous analyte, and systems that deal with the analyte in the liquid phase. To date, the first group is composed solely of thermodenuders, devices that rely on thermally cycled sorption-desorption steps. The second group includes wet diffusion denuder-scrubbers and devices that are cyclically sorbent-coated and washed. 

The principal implication of these studies for the accurate measurement of strong acids in gaseous and aerosol phases is that sampling must be performed in a way that does not disturb the equilibrium significantly in the process. This necessity has led to the development of the diffusion denuder sampler (61), which measures nitric acid after its removal to the walls of a... 

One procedure that is widely used to circumvent these complications is to remove ambient ammonia from the sampled air without removing particles by inserting one of several types of diffusion denuders upstream from the filter(s). In fact, in a recent Environmental Protection Agency (EPA)-sponsored intercomparison of methods for determination of strong acid content of aerosols, all but one protocol utilized an ammonia denuder (63), and all used an impactor or cyclone to remove coarse particles. The presence of this denuder clearly prevents neutralization of acidic aerosols by ammonia but also disturbs the gas-aerosol equilibrium between sulfate-nitrate aerosols and gaseous species. Ammonia and nitric acid are released from the depositing particles (64, 65) and must be collected downstream if accurate particulate ammonium and nitrate determinations are to be made. If equal amounts of ammonia and nitric acid are released, then the absolute [H+] (neq/m3) will not be altered. No specific evidence is available in the literature to demonstrate alteration of the observed [H+] as the result of reequilibration, but this area deserves further study. 

Eatough, D.J., A. Wadsworth, D.A. Eatough, J.W. Crawford, L.D. Hansen, and E.A. Lewis, 1993. A multi-system, multi-channel diffusion denuder sampler for the determination of fine particulate organic matter in the atmosphere. Atmos. Environ. 27 1213-1219. 

Gundel, L.A. and D.A. Lane. 1999. Sorbent-coated diffusion denuders for direct measurement of gas/particle partition by semivolatile organic compounds. In Lane, D.A., Ed., Gas and Particle Measurements of Atmospheric Organic Compounds. Gordon and Breach Science Publishers, Amsterdam, pp. 287-332. 

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