Filter collection

Typical new equipment design efficiencies are between 99 and 99.9%. Older existing equipment have a range of actual operating efficiencies of 95 to 99.9%. Several factors determine fabric filter collection efficiency. These include gas filtration velocity, particle characteristics, fabric characteristics, and cleaning mechanism. In general, collection efficiency increases with increasing filtration velocity and particle size. 

Ceramic Filter. The ceramic filter collects, volatilizes, and destroys particulates and condensible organics emitted from industrial process streams, such as paint spray, lost foam casting, condensible organics, tenter frames, and cured rubber... 

So far the discussion has revolved around completely automated dissolution. Meaning that media is prepared, dispensed into the vessels, tablets dropped, sampled, filtered, collected or read, and lines and vessels washed. This series of events must be reproduced multiple times without human intervention after it has been initiated (Fig. 3). 

Gatz (8) applied a principal components analysis to aerosol composition data for St. Louis, Mo taken as part of project METROMEX (13-1 t). Nearly 400 filters collected at 12 sites were analyzed for up... 

FIGURE 6.37 (a) Surface-level 03 at Alert, Canada, and (b) filter-collected bromide (f-Br) during an ozone depletion episode (adapted from Barrie el al., 1988). 

Fitz, D. R., G. J. Doyle, and J. N. Pitts, Jr., An Ultra-High Volume Sampler for the Multiple Filter Collection of Respirable Particulate Matter, J. Air Pollut. Control Assoc., 33, 877-879 (1983). 

Flessel, P., Y. Y. Wang, K.-I. Chang, J. J. Wesolowski, G. N. Guir-guls, I.-S. Kim, D. Levaggi, and W. Siu, "Seasonal Variations and Trends in Concentrations of Filter-Collected Polycyclic Aromatic Hydrocarbons (PAH) and Mutagenic Activity in the San Francisco Bay Area, J. Air Waste Manage. Assoc., 41, 276-281 (1991). 

Lee, F. S. C., W. R. Pierson, and J. Ezike, The Problem of PAH Degradation during Filter Collection of Airborne Particulates—An Evaluation of Several Commonly Used Filter Media, in Polynuclear Aromatic Hydrocarbons Chemical and Biological Effects... 

Air is drawn through a filter that consists of, or is coated with, a substance that takes up the species of interest. The filter is then extracted and the ions of interest are measured. For most species of interest, care must be taken to avoid interference from particles. For example, as discussed later, filter collection of HN03 will have a contribution from particulate nitrate if particles are not removed first. Figure 11.22 shows a typical filter pack used to measure gaseous HNO-, and NH-, (Anlauf et al., 1988). 

Filters collect liquid and solid particles by mechanisms including diffusion, impaction, interception, electrostatic attraction, and sedimentation onto the filter while allowing the gas to pass through. The types commonly used in atmospheric particulate collection are membranes, fibrous mats, or porous sheets. Different filter materials are used depending on the particular type of measurement being carried out, including Teflon, quartz fiber, nylon, silver, cellulose filters, glass fibers, and polycarbonate. The characteristics of each are summarized by Chow (1995). 

The distribution of estimated biases for these methods is shown in Figure 3. Except for a bias of zero, the methods tend to be distributed evenly in the -10% to 10% bias region. The high proportion of zero-bias methods may be explained by the number of filter collection methods which have 100% collection efficiency many of these methods use low-biased analysis techniques, particularly atomic absorption spectroscopy. 

Precipitation during the 12-hour period before filter collection decreased the radon concentration, as shown in Table II for three stability categories. The effect is especially apparent at high stabilities radon concentrations were almost two-fold lower during precepitation at sta-... 

Average monthly morning concentrations of radon in air increased with average monthly values of atmospheric stability during the 12 hours before filter collection, but there was appreciable scatter of values about lines of best fit. The squared correlation coefficient was 0.53 for a linear relation between radon concentration and stability. Lower correlations applied to stability values averaged over periods longer or shorter than 12 hours. Precipitation during the 12-hour period before collection decreased radon concentrations. 

PAN is a potential interferent with daytime concentration maxima that can coincide with the HN03 maxima. However, early work by Joseph and Spicer (23) and later work by Fahey et al. (24) indicated that PAN is not a significant interferent in HN03 measurements relying on nylon-filter collection. The change in nylon-filter composition introduces a small degree of uncertainty to this conclusion. 

Nylon after-filter Collect HNO3 Collection of volatilized PN retention of HONO retention of unidentified species yielding N03"... 

This approach was developed further by Bidleman and co-workers (65, 70-72) and included the use of filter-collected particles and PUF traps to operationally define the required parameters. For example, the predicted influence of temperature on the vapor-particle partitioning of fluoranthene... 

The detection limit for measuring a species by filter collection and subsequent analysis is determined either by the uncertainty in the filter blank, that is, the variability in the amount of a species in an unexposed filter, or by the limit of detection imposed by the analytical method. Most frequently, the limit of detection is determined by blank variability, thus care in preparation and handling of filters is important when using such systems for aircraft sampling, particularly if sampling is conducted in remote areas where concentrations are low. In this regard, it is crucial to establish the blank... 

Multifilter sampler (total nitrate, sulfate, and acidic chloride filter collection postflight aqueous extraction and ion chromatography 39... 

Descriptions of analytical methods for strong acid and acidic sulfate content of atmospheric aerosols have been reviewed (6-10). Methods for acidic aerosol determination are reviewed in this chapter according to the measurement principle either filter collection and post-collection extraction, deriv-atization or thermal treatment, and analysis or in situ collection (real-time or stepwise) and analysis. 

Short HO radical lifetimes in the dark prevent the collection of ambient air samples for later analysis, except perhaps for the case of filter collection techniques that use a spin-trapping reagent (28). Furthermore, rapid reactivity of HO with surfaces mandates careful attention to the sampling train used to move ambient air into a more amenable analysis environment. 

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