Coarse particles 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. 

This result may be deceptive, however, as we had to eliminate the many studies from Cols. 2 and 3 that contained no size Information, so the two sets of averages are not for the same populations of plants. A further problem with these data may also be the Inclusion of particles up to 2.5-pm dlam, whereas, recent studies (44, 46) indicate that the large changes of composition occur below about 0.5-pm dlam. Thus, our "fine" particles In Table IV Include particulate mass between 0.5 and 2.5 ym that Is chemically similar to larger particles, which reduces the Rvalues. We made the cut at 2.5 ym to develop components for separate CEBs of fine and coarse particles In ambient air, which are commonly divided at about that point. 

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. 

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.

Analysis of these data show that concentration of each chemical element was higher in TSP during Yellow sand cases than during non-Yellow sand cases by 2-3 orders. Most elements were indicated to have higher concentrations in coarse particles than in finer ones. This could be related both to the chemical composition of soil from the Gobi desert as the main source of coarse TSP and to the adsorption of heavy... 

The sources and chemical compositions of the fine and coarse urban particles are different. Coarse particles are generated by mechanical processes and consist of soil dust, seasalt, fly ash, tire wear particles, and so on. Aitken and accumulation mode particles contain primary particles from combustion sources and secondary aerosol material (sulfate, nitrate, ammonium, secondary organics) formed by chemical reactions resulting in gas-to-particle conversion (see Chapters 10 and 14). 

Our analysis so far has assumed that all particles in the aerosol population have similar chemical composition. Meng and Seinfeld (1996) numerically investigated cases where the aerosol population consists of two groups of particles with different compositions. They concluded that while the timescale of equilibration of the fine aerosol particles is indeed on the order of minutes or less, the coarse particles may require several hours or even days to achieve thermodynamic equilibrium with the surrounding atmosphere. 

Atmospheric aerosols consist of particles ranging in size from a few tens of angstroms (A) to several hundred micrometers. Particles less than 2.5 /xm in diameter are generally referred to as fine and those greater than 2.5 /xm diameter as coarse. The fine and coarse particle modes, in general, originate separately, are transformed separately, are removed from the atmosphere by different mechanisms, require different techniques for their removal from sources, have different chemical composition, have different optical properties, and differ significantly in their deposition patterns in the respiratory tract. Therefore the distinction between fine and coarse particles is a fundamental one in any discussion of the physics, chemistry, measurement, or health effects of aerosols. 

Potential Exposure to Airborne Particles Atmospheric particles of different sizes have been shown to act predominantiy as inflammatory or cytotoxic-apoptotic particles (1, 2). Testing urban samples collected using HVCI showed coarse particles (PM 10 to 2.5) to be more capable of causing cells to release inflammatory cytokines such as tumor necrosis factor alpha (TNFa), and interleukins 6 and 8 (IL6, IL8) than were fine (PM 2.5 to 0.2) particles. The smaller fine particles (PM 2.5 to 0.2) have less infiammatory potential (1,2,30). Perhaps the reason is because of less mass, or a greater possibility of altering the active surface of smaller particles. For example, if surface area is increased it will increase the potential to produce inflammation. For this reason fine particles have quite variable inflammatory potential. The degree to which specific chemical composition plays a role is not understood sufficiently at this time. 

Kim K-H, Kim MY (2003) The effects of Asian Dust on particulate matter fractionation in Seoul, Korea during spring 2001. Chemosphere 51(8) 707-721 Kim K-H, Choi G-H, Kang C-H, Lee J-H, Kim J-Y, Youn Y-H, Lee S-R (2003) The chemical composition of fine and coarse particles in relation with the Asian Dust events. Atmos Environ 37 753-765... 

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