Coarse chemical composition

Airborne particulate matter, which includes dust, dirt, soot, smoke, and liquid droplets emitted into the air, is small enough to be suspended in the atmosphere. Airborne particulate matter may be a complex mixture of organic and inorganic substances. They can be characterized by their physical attributes, which influence their transport and deposition, and their chemical composition, which influences their effect on health. The physical attributes of airborne particulates include mass concentration and size distribution. Ambient levels of mass concentration are measured in micrograms per cubic meter (mg/m ) size attributes are usually measured in aerodynamic diameter. Particulate matter (PM) exceeding 2.5 microns (/i) in aerodynamic diameter is generally defined as coarse particles, while particles smaller than 2.5 mm (PMj,) are called fine particles. 

When considering the impact of uptake by aerosol, the chemical composition of the aerosol is also likely to be significant. Bates et al. (1998, 2001) measured strong variations in the chemical composition of the Aitken, accommodation and sea-salt dominated coarse modes that would influence the free radical uptake rates, particularly the extent of aerosol acidification. Without data on the size segregated aerosol chemical composition during SOAPEX-2 and the relevant laboratory data, it is not possible to calculate accurate accommodation coefficients. 

Mittal, et al. reported the proximate chemical composition of a number of different samples collected in the model card room at North Carolina State University (31). Samples in this study included a coarse trash which was comprised of relatively large, mostly lint-free particulate matter that fell to the floor of the condenser filter chamber in a Pneumafil filter system (Model FCV8-3MTRK) (31). The second sample set was separated by the sonic sifting procedure from the condenser trash. Another set of samples was collected from an electrostatic precipitator located in the air conditioning return of the model card room. Results of ash analyses are shown in Table VII. 

In the subsurface, kerosene volatilization is controlled by the physical and chemical properties of the solid phase and by the water content. Porosity is a major factor in defining the volatilization process. Galin et al. (1990) reported an experiment where neat kerosene at the saturation retention value was recovered from coarse, medium, and fine sands after 1, 5, and 14 days of incubation. The porosity of the sands decreased from coarse to fine. Figure 8.9 presents gas chromatographs obtained after kerosene volatilization. Note the loss of the more volatile hydrocarbons by evaporation in all sands 14 days after application and the lack of resemblance to the original kerosene. It is clear that the pore size of the sands affected the chemical composition of the remaining kerosene. For example, the fractions disap-... 

Some degree of fractionation as function of distance from the power station smoke stack is to be expected coarse particles will fall out in the immediate vicinity of the power station, whereas fine fly ash will be transported further, and gaseous emissions might be expected to be transported the furthest. Thus, from the point of view of environmental health, not only the chemical composition of emitted particles and aerosols, but also their size, is relevant (Teinemaa et al. 2002). As particulate matter is dominated by basic oxides (e.g., CaO) and gaseous emissions by acidic gases (e.g., CO2, SO2), this fractionation will influence the pH of... 

Chemical Composition Aerosol composition measurements have most frequently been made with little or no size resolution, most often by analysis of filter samples of the aggregate aerosol. Sample fractionation into coarse and fine fractions is achieved with a variety of dichotomous samplers. These instruments spread the collected sample over a relatively large area on a filter that can be analyzed directly or after extraction Time resolution is determined by the sample flow rate and the detection limits of the analytical techniques, but sampling times less than 1 h are rarely used even when the analytical techniques would permit them. These longer times are the result of experiment design rather than feasibility. Measurements of the distribution of chemical composition with respect to particle size have, until recently, been limited to particles larger than a few tenths of a micrometer in diameter and relatively low time resolution. One of the primary tools for composition-size distribution measurements is the cascade impactor. 

The most common way in aerosol science to represent PND data is in terms of various modes. Generally, these modes are nucleation (typically in the 1-30 nm range), Aitken (typically in the 20-100 nm range), accumulation (typically in the 30-300 nm range) and coarse (typically over 300 nm size range). Each mode contains different sources, size range, formation mechanisms, and chemical compositions [30],... 

In this particular example, estimates for both free energy parameters g and ga of the coarse-grained model are obtainable from more detailed molecular models albeit that strictly speaking they depend not only on the chemical composition and structure of the molecular building blocks but in principle also on the solvent properties. It is important to stress again for it is often ignored, the solvent molecules not only drive the assembly but have been shown to play an active role in structural reorganizations of supramolecular assemblies (Bouteiller et al., 2005 Jonkheijm et al., 2006). Ideally, their influence should not be absorbed in adjustable parameters as is almost always done. 

Nanomaterials are composed of structural entities - isotropic grains or particles, rods, wires, platelets, layers - of size, at least in one dimension, between 1 and 100 nm [1-3]. Larger particles are called submicron particles, smaller ones are known as clusters. Some physical properties of nanomaterials [4-6] differ from those of coarse-grained materials of the same chemical composition due to two essential features ... 

The different size modes reflect differences in particle sources, transformations, and sinks (Finlayson-Pitts and Pitts 2000). For example, coarse particles are generated by mechanical processes such as wind erosion of soil, wave action in the oceans, and abrasion of plant material. In contrast, many of the fine particles in the atmosphere are produced from either primary emissions from combustion sources or via atmospheric gas-to-particle conversions (i.e., new particle formation). The relative and absolute sizes of particle modes, as well as the number of modes, can vary greatly in different locations and at different times. In addition, the chemical composition of particles within one size... 

The coarse mode is largely composed of primary particles generated by mechanical pro-ce.sses such as soil dust raised by llie wind and/or vehicular traffic and construction activities. Coarse particles arc also emitted in gu.ses from industrial sources such as coal combustion and smelting. The coarse mode often peaks at about lO/tin. The chemical composition of the coarse mode is for the most part the sum of the chemical components of the primary aerosol emissions. However, there may be some contributions from gas-to-particle conversion, such as ammonium nitrate, as discussed below. 

Figures 7-6 and 7-7 show the burning rate of AP-HTPB composite propellants at 243 K and 343 K. The propellants are composed of bimodal fine or coarse AP particles with or without catalysts. The catalyst is 2,2-bis (ethylferrocenyl) propane (BEFP). The chemical compositions of the propellants are shown in Table 7-2. All burning rates increase linearly in a In p versus In r plot in the pressure range 1.5-5 MPa, and also increase with increasing initial propellant temperature at constant pressure 13. The burning rate increases with decreasing AP particle size, and the temperature sensitivity decreases with decreasing AP particle size, i.e., with increasing burning rate.

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