Airborne particle parameters

Moller, M., I. Alfheim, S. Larssen, and A. Mikalsen, Muagenicity of Airborne Particles in Relation to Traffic and Air Pollution Parameters, Environ. Sci. Technol., 16, 221-225 (1982). 

Lingard JJN, Agus EL, Young DT, Andrews GE, Tomlin AS (2006) Observations of urban airborne particle number concentrations during rush-hour conditions analysis of the number based size distributions and modal parameters. J Environ Monit 8 1203-1218... 

One of the most important projects in progress in the field of hybrid receptor modeling is the Allegheny Mountain study by Pierson et al. of Ford Motor Co. (This Volume). Concentrations of many ions, major, minor and trace elements in airborne particles, rain, dew and fog and other parameters were measured at Allegheny Mt., PA and Laurel Hill, 35 km to the northwest, from 5 to 28 Aug 1983, approximately simultaneously with the Deep Creek Lake studies discussed above. These two huge data sets are now nearly complete and ready for detailed interpretations by the participants and other researchers in the field. In particular, Keeler is working with the Ford group to apply the Samson method to the data. 

Here the parameter v represents the real part of the index and k the imaginary part. The real part represents scattering and the imaginary part, absorption. Carbon particles, e.g., have a refractive index of about (2 - i). In general, for airborne particles, the real part of the refractive index for most materials lies between 1.0 and 1.6, and the imaginary part between 0 and 1. Refractive indices of various materials are given in Table 16.4. 

Miller, A, Alfheim, I., Larssen, S., and Mikalsen, A. Mutagenicity of airborne particles in relation to traffic and air pollution parameters 1982, Environ. Sci. Technol. 16, pp. 221-225. 

Table 3. Parameters Commonly Analyzed for in Airborne Particles...

Particle size emerges as a critical parameter in eqn (7) iv d ), thus if the settling distance is Im, a 50 pm-diameter sphere of SGl-0 will cover that distance at its terminal velocity in 13 s whereas a 10 pm diameter sphere of the same SG will require 5 5 min. Dorman has shown the change in with d outside the viscous range (i e up to 10" ) for a Imm-diameter sphere of SG 1 0 the terminal velocity at atmospheric pressure and 20°C is around 40m/s. Under comparable conditions a 0 1 pm-diameter sphere has a terminsd velocity of approximately 3 mm/h. Particle size therefore emerges as a dominant factor in the dynamics of airborne particles, and only the very smallest particles are capable of apparently motionless suspension in still air. 

In the case of significant accidental exposures, it will often be necessary to use parameter values in the calculation of tissue or organ equivalent doses and effective dose that ate specific to the conditions of exposure and to the individual. Similarly, in routine situations it may be necessary to take account of the particular circumstances of exposure rather than using default parameters. The new model for the respiratory tract [34] adopts an AMAD of 5 pm as a default particle size when no specific information is available. Regional deposition of airborne particles is subject to the mechanisms of sedimentation, impaction and diffusion. Deposition throughout the respiratory system and hence inhalation dose coefficients depend upon aerosol parameters, such as the AMAD. Similarly, ingestion dose coefficients depend upon the choice of an appropriate/j value. 

Particle density is an important parameter in defining the aerodynamic behaviour of airborne particles. Small quantities of selected batches (ca. Ig of FS3, FS4, FS5 and FS6) were placed in the sample chamber of a helium pycnometer (model 1305 Multivolume Helium Pycnometer, Micromeritics Ltd, Basingstoke, UK), and the particle density determined from the volume of helium displaced, assuming there were no inaccessible voids within the particles. The four measurements (each of which was the mean of 4 to 6 separate determinations (Table 3)) were within the density range of 2.91 to 3.26 X 1Q3 kg m-3 quoted for natrojarosite. These studies confirm the validity of the x-ray diffraction measurements, and also indicated that the particles were substantially free of internal voids. 

More accurate determination of reflective radiative surface emissivity The radiative emissivity of the composite surface, similarly to the heat transfer coefficient (4), is a function of the resin-char composition of the surface at any point during the combustion process, and is also affected by the surface profile and roughness. Hence it is not sufficient to use one value for this parameter in the model for the duration of the exposure event. However, characterizing the in-situ dynamic behavior of this parameter in a turbulent combustive atmosphere in the presence of soot, flame and airborne particles is a particularly challenging task, so that modelers may well be forced to rely on binary before/after shifts in the emissivity based on measurements made on the virgin resin-fiber composite and char-fiber residue respectively. 

Figure 4 Schematic representation of the relation between different parameters used to describe the size distribution of airborne particles. (From Ref 106.)...

The measurements of trace species—both gases and particles—and of atmospheric parameters that were measured during the Airborne Antarctic Ozone Expedition and the Airborne Arctic Stratospheric Experiment are given in Table I. These techniques have quite different requirements that are dictated by the detection technique and the way an air sample is handled. 

The link between exposure to air pollutants and adverse health effects is well established, but the causal biological mechanisms are not clear and this is especially the case for particulate matter health effects. Airborne particulate matter is extremely variable in chemical composition, size and morphology all parameters of possible health relevance. This and the different health endpoints affected by exposure to ambient PM make the situation very complex. It may well be that more than one particle characteristic is needed to effectively describe the harmful outcomes of exposure. Possible parameters under discussion are particle number concentration, which is dominated by particles below 100 nm in size the so-called ultrafines [33], particle surface area concentration, which is dominated by particles around 200-800 nm in diameter [34, 35], black carbon or black smoke [36], or the reactivity of particles with respect to redox reactions, or their potential to form radical oxidative species (ROS) [37]. These and some other alternative particulate indicators are currently discussed [38] and investigated in several large European and US studies such as ESCAPE and Transphorm2. 

Biological, chemical, and physical effects of airborne metals are a direct function of particle size, concentration, and composition. The major parameter governing the significance of natural and anthropogenic emissions of environmentally important metals is particle size. Metals associated with fine particulates are of concern particles larger than about 3-fjim aerodynamic equivalent diameter are minimally respirable, are ineffective in atmospheric interactions, and have a short air residence time. Seventeen environmentally important metals are identified arsenic, beryllium, cadmium, chromium, copper, iron, mercury, magnesium, manganese, nickel, lead, antimony, selenium, tin, vanadium, and zinc. This report reviews the major sources of these metals with emphasis on fine particulate emissions. 

The vortical method of coating deposition consists of immersion of the heated article in the fluidized bed of the polymer powder formed by blowing a gas flow through the porous bottom of a vessel containing the powder (Fig. 3.23). Under certain parameters of the gas flow, the immovable layer of powder particles poured into the vessel to the level Ho expands up to the level H. The particles acquire mobility and transfer into the airborne state. The criterion for this change is a constant value of the gas pressure differential in the powder bed volume [52]. 

Many of the transport properties of fine particles are comparable to those of gas ph2ise species. They migrate by convective diffusion and can remain in the air of a room for hours and even days, depending on the air exchange rate of the room. In the absence of thermophoretic forces or electric fields, they deposit with roughly equal propensity on all surface configurations and are more able to penetrate narrow spaces than coarse particles. The ratio of the surface accumulation rate (units of mass per unit area per unit time) to the airborne concentration (units of mass per unit volume) is a useful physical parameter that is commonly referred to as the deposition velocity (units of distance divided by time). The deposition velocity is the transfer... 

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