Particulate using measured ambient

Black smoke (BS) is a particulate measure that typically contains at least 50% respirable particulates smaller than 4.5 mm in aerodynamic diameter, sampled by the British smokeshade (BS) method. The reflectance of light is measured by the darkness of the stain caused by particulates on a white filter paper. The result of BS sampling depends on the density of the stain and the optical properties of the particulates. Because the method is based on reflectance from elemental carbon, its use is recommended in areas where coal smoke from domestic fires is the dominant component of ambient particulates. 

Receptor models are used to determine the source contributions to ambient particulate matter loadings at a sampling site based on common properties between source and receptor. This is in contrast to a source model which starts with emission rates and meteorological measurements to predict an ambient concentration. 

Nearly 23 years of hourly observations on particulate matter concentrations have been collected at downtown Los Angeles and at six other sites in the Los Angeles area using a tape sampler calibrated to read in Km units. The design of these samplers is as described by Hall (20). Ambient air is drawn through a one square-inch (5.07 cm ) area of filter paper at a rate of 25 ft per hour (11.8 1pm) for 51.5 min of each hour. The darkness of the spot developed on the filter is measured by the ratio of the intensity of the reflected light from clean white filter paper, R, to reflected light from the aerosol deposit, R. As used by tfie air pollution control district, the Km unit is related to reflectance by the formula (21). 

As discussed in Chapter 9.C, ambient particulate matter contains inorganic elements and ions, including trace metals, as well as graphitic (elemental) carbon and a wide variety of organic compounds and water. Techniques in common use to measure these species are discussed very briefly here. For further details of the principles behind these techniques, the reader should consult instrumental analysis texts (e.g., Skoog et al., 1998). Specific applications of various methods to particles in the atmosphere are described in the book edited by Spurny (1986) as well as the references at the end of this chapter. 

Inorganic ions such as NHj, SO4-, and NO are major components of ambient particulate matter and a wide variety of methods have been used to measure their concentrations. A few of the methods most commonly used are summarized in Table 11.12 and discussed briefly in the following sections. 

The difference between IGC and conventional analytical gas-solid chromatography is the adsorption of a known adsorptive mobile phase (vapour) on an unknown adsorbent stationary phase (solid state sample). Depending on experiment setup, IGC can be used at finite or infinite dilution concentrations of the adsorptive mobile phase. The latter method is excellent for the determination of surface energetics and heat of sorption of particulate materials [3]. With IGC at finite dilution, it is possible to measure sorption isotherms for the determination of surface area and porosity [4], The benefits of using dynamic techniques are faster equilibrium times at ambient temperatures. 

Practical methods also have been reported for semicon-tinuous measurement of nitrate and carbon in particles from ambient air. For example, an instrument for nitrate monitoring uses collection of particles on an impactor surface, followed by flash volatilization and determination of the nitrate present using a chemiluminescence technique. Ion chromatographs also have been adopted for semicontinuous determination of gaseous and particulate nitrate. Real-time carbon analyzers also are available, one of which uses differential thermal analysis of impactor-collected material. 

It would be desirable to have simple tests capable of characterising the fluidisation behaviour or flowability of particulate materials on the basis of their bulk properties. To this end, Carr19 developed a system to characterise bulk solids with respect to flowability. Table 6 summarises the properties which are determined. In Carr s method a numerical value is assigned to the results of each of these tests, and is summed to produce a relative flowability index for that particular bulk material. Given the extensive use of these empirical techniques in academia and industry, a brief review on the subject is reported here. Nevertheless, it should be emphasised that these techniques allow measurements of the flow-ability or cohesion of materials solely in their stationary or compressed status and at ambient conditions. A direct relationship between these... 

Brown, R.J.C., Yardley, R.E., Brown, A.S., Milton, M.J.T. Sample matrix and critical interference effects on the recovery and accuracy of concentration measurements of arsenic in ambient particulate samples using ICP-MS. J. Anal. At. Spectrom. 19, 703-705 (2004)... 

The relation between ambient levels and precursor emissions is somewhat easier to identify for particulates than for ozone, because the chemical composition of individual particulates provides evidence for their origin sulfate particulates are associated with sulfur dioxide emissions organic particulates with specific VOCs, and so on. A variety of statistical methods have been used to identify source types for particulates based on chemical composition, especially in terms of trace metal components (e.g., Henry, 1992 Seinfeld and Pandis, 1998). This type of analysis requires sophisticated measurements of the chemical composition of individual particulates, rather than the more common measurement of summed concentrations. Statistical methods have also been used to gain information about ozone and ozone precursors (e.g., Buhr et al., 1995 Stehr et al., 2000). 

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