Impactor samples system

Sampling. Four aerosol samples were collected isokinetically on July 26, 1979, at ports on the inlet duct of the ESP at Plant A two were taken with 62-mm fluoropore filters and two were taken with the University of Washington MKV Cascade impactor (1 ). At plant D, samples were collected over a 6-day period at ports both in the outlet duct of the ESP (i.e., upstream of the FGD system) and at the 91-m level of the stack. Eleven fluoropore filter, 1 MKV, and 4 MKIII impactor samples at each location, giving a total of 22 filter, and 8 MKIII samples. A single MKV sample was also collected in-stack at reduced pressure at plant D during the 6-day period. Polycarbonate material coated with apiezon L vacuum grease and 62 or 47-mm-diam, l-pm pore Fluoropore filters were used as back-up filters in the MKV impactor. 

Because a filter sample includes particles both larger and smaller than those retained in the human respiratory system (see Chapter 7, Section III), other types of samplers are used which allow measurement of the size ranges of particles retained in the respiratory system. Some of these are called dichotomous samplers because they allow separate measurement of the respirable and nonrespirable fractions of the total. Size-selective samplers rely on impactors, miniature cyclones, and other means. The United States has selected the size fraction below an aerodynamic diameter of 10 /xm (PMiq) for compliance with the air quality standard for airborne particulate matter. 

Figure 4.2 shows the complete CBMS II system. The main unit is comprised of three modules, the Biosampler Module, the Sample Introduction Module (SIM), and the Mass Spectrometer Module. The Biosampler Module houses the virtual impactor air particle concentrator and is only needed for the biological agent monitoring mode. The Sample Introduction Module contains the multiport sampling valve with its three input connections ... 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

All impactor and filter samples were analyzed for up to 45 elements by instrumental neutron activation analysis (INAA) as described by Heft ( ). Samples were irradiated simultaneously with standard flux monitors in the 3-MW Livermore pool reactor. The x-ray spectra of the radioactive species were taken with large-volume, high-resolution Ge(Li) spectrometer systems. The spectral data were transferred to a GDC 7600 computer and analyzed with the GAMANAL code (1 ), which incorporates a background-smoothing routine and fits the peaks with Gaussian and exponential functions. 

Frequently, a major limitation of DS-based collection systems is that they operate at substantially subquantitative collection efficiencies at the typical sampling rates used. This situation increases the probability of error because of large thermal variations that affect diffusive transport. For these reasons, should wet denuders (vide infra) prove to be viable continuous collection devices, they may well replace DS-based systems. Their ability to more quantitatively remove gases may also spur the development of combined gas-particle analyzer systems in which, for example, the acid gases are removed by the denuder and analyzed the particles are then collected by the impactor equivalent of a wet denuder, and the acidity associated with... 

The fact that fine atmospheric particles are enriched in a number of toxic trace species has been known since the early 1970s. Natusch and Wallace (20, 21) observed that the fine particles emitted by a variety of high-temperature combustion sources follow similar trends of enrichment with decreasing particle size as observed in the atmosphere, and they hypothesized that volatilization and condensation of the trace species was responsible for much of the enrichment. Subsequent studies of a number of high-temperature sources and fundamental studies of fine-particle formation in high-temperature systems have substantiated their conclusions. The principal instruments used in those studies were cascade impactors, which fractionate aerosol samples according to the aerodynamic size of the particles. A variety... 

The early history of Earth is greatly influenced by the probable impact of a Marssized body to form the Moon. Core-formation models suggest both Earth and the impactor were already differentiated by the time of the impact (Tonks Melosh 1992). The lack of a clear182W excess in uncontaminated lunar samples implies that the Moon-forming impact took place >50 Myr after the start of the Solar System (Touboul et al. 2007). The oldest known lunar samples are 150 Myr younger than CAIs, based on Sm-Nd dating (Touboul etal. 2007), which provides a lower limit on the Moon s age. 

Springer (5) using a sampling probe-impactor system for a similar cruise condition with an eight-cylinder Chevrolet engine. The reported im-pactor data, taken on a mass basis, was converted to a number basis here assuming a particulate density of 1.8 g/cm and normalized to gasoline consumption to facilitate comparison. 

One can turn these arguments around, however, and use the compositions of lunar samples to define the composition of Theia, assuming the impactor produced most of the material in the Moon (MacFarlane, 1989). Accordingly, the similarity in oxygen isotopes and trace siderophile abundances between the Earth and Moon provides evidence that Earth and Theia were neighboring planets made of an identical mix of materials with similar differentiation histories (Halliday and Porcelli, 2001). Their similarities could relate to proximity in the early solar system, increasing the probability of collision. 

Figure 6 Different inlets used to couple a cascade impactor to an aerosol delivery system. The inlets range in volume from 66 to 1080mL [92] and collect varying amounts of drug, depending on their volume. This in turn affects the amount of aerosol sampled by the impactor.

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