Environ. Sci. Technol. 1993, 27, 2497-250 1
Development and Evaluation of a Glass Honeycomb DenuderIFilter Pack System To Collect Atmospheric Gases and Particles P. Koutrakis,' C. Sloutas, S. T. Ferguson, and J. M. Wolfson
Harvard University, School of Public Health, 665 Huntington Avenue, Boston, Massachusetts 021 15 James
D. Mullk and Robert M. Burton
U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711 Currently available annular denuder/filter pack technology has been extremely useful for atmospheric studies but has a relatively high cost for both instrumentation and operation. We have developed an alternative system which maintains and improves operational features while being more compact. The main, novel feature of the proposed system is the denuder component, which has a large number of small hexagonal glass tubes sealed inside an outer glass tube. The new system has the following advantages: (1)both the initial cost and the labor required for processing are much less than those of the annular denuder; (2) a length of only 3.8 cm yields the same collection capability as a length of 21 cm for the annular denuder, allowing a much more durable system; (3) this length also allows the use of several more denuders for simultaneous collection of a greater variety of gases; and (4) this new system is more convenient for large-scale monitoring studies. This paper presents the results from the performance evaluation of the impactor/honeycomb denuder/filter pack system. The tests include the impactor size cutoff determination, the honeycomb denuder efficiency and capacity measurements, and measurement of losses of acidic and basic gases on the sampler inlet surfaces.
Introduction During the last decade, diffusion denuders have been used in a variety of atmospheric monitoring studies to collect gaseous atmospheric pollutants (2,4-7). In these studies, glass or metallic hollow tubes were coated to selectively collect the different gases while allowing other gases and particles to penetrate. However, these tubular denuders presented high collection efficiencies only for low collection flow rates (less than 1 L/min). In 1983, Possanzini et al. developed an annular denuder that can efficiently collect atmospheric gas at considerably higher flows (higher than 10 L/min) (13). Use of a series of two annular denuders (coated with sodium carbonate and citric acid, respectively) makes possible the collection of both acidic gases, such as SO2, HN03, " 0 2 , and gas-phase Also, the use organic acids, and basic gases, such as "3. of a filter pack downstream from the annular denuder series allows the simultaneous collection of particles. In this paper we will discuss the development and evaluation of an impactor/honeycomb denuder/filter pack system, which includes features of the aluminum honeycomb/filter pack system we developed a few years ago (8). The main feature of the proposed system is the denuder component, which has a large number (212) of small hexagonal tubes sealed inside an outer glass tube. The new system is considerably smaller than the annular denuder system and can be easily used for large field studies 0013-938X/93/0927-2503$04.00/0
0 1993 Amerlcan Chemlcal Soclety
Filter Pack
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Flgure 1. Honeycomb denuder sampler.
(with lower shipping and field operation cost@. Therefore, the glass honeycomb denudedfilter pack system will be more suitable for use by many researchers for atmospheric sampling.
Methods and Materials SamplerDescription. The honeycombdenuderlfilter pack system, shown in Figure 1, has three essential features: (a) an impactor to remove coarse particles ( d , > 2.1 ym) from the air sample; (b) two glass honeycomb denuders; and (c) a two-stage filter pack to collect fine particles. The inlet has a short elutriator, which points downward to help exclude the largest particles. The circular array of nozzles for 10 L/min causes particles larger than 2.1 gm to impact on the impactor plate, a ring of sintered stainless steel coated with mineral oil. A transition section allows the sample air to flow smoothly and have uniform ffow through the individual honeycomb tubes of the first denuder. A Teflon (du Pont) coating minimizes interaction between internal surfaces and reactive gases. The first honeycomb denuder (coated with sodium carbonate/ glycerolto collect acid gases) is separated by an inert spacer from the second denuder (coated with citric acid/glycerol to collect basic gases). A stainless steel spring keeps the components in place. A third denuder can be used, if desired. The two-stage filter pack has a Teflon filter to collect fine particles (
