Particulate matter sizes

Polycyclic aromatic hydrocarbons (PAHs) represent a class of compounds that contain two or more fused benzene rings. They are environmental pollutants and the most ubiquitous, benzo[a]pyrene (B[a]P), has been upgraded by the International Agency for Research on Cancer to a Group 1 or known human carcinogen [1]. PAHs are products of fossil fuel combustion they are a component of fine particulate matter (size 2.5pm) and as a consequence contaminate the air we breathe, the soil and water supply, and enter the food chain [2, 3]. They are also introduced artificially into smoked, cured, and barbecued food [4, 5], Finally, they are present as a complex mixture in tobacco smoke and second-hand smoke, and are suspect causative agents in human lung cancer [6]. 

The total suspended particulate (TSP) measuring networks, managed by local and state agencies, currently numbering about 250 sites, measure lead via official Federal methods (40 CFR Part 40, Appendix G) in particulate matter sized up to 30 pm. The retention of the TSP networks is driven by the regulatory stmctore of the previous and current ambient air lead primary and secondary standards. Locations of these sites are depicted in U.S. EPA (2006, Ch. 3). 

The calculation shows how rapidly a droplet changes in diameter with time as it flows toward the plasma flame. At 40°C, a droplet loses 90% of its size within alxtut 1.5 sec, in which time the sweep gas has flowed only about 8 cm along the tube leading to the plasma flame. Typical desolvation chambers operate at 150°C and, at these temperatures, similar changes in diameter will be complete within a few milliseconds. The droplets of sample solution lose almost all of their solvent (dry out) to give only residual sample (solute) particulate matter before reaching the plasma flame. 

When a liquid or solid substance is emitted to the air as particulate matter, its properties and effects may be changed. As a substance is broken up into smaller and smaller particles, more of its surface area is exposed to the air. Under these circumstances, the substance, whatever its chemical composition, tends to combine physically or chemically with other particles or gases in the atmosphere. The resulting combinations are frequently unpredictable. Very small aerosol particles (from 0.001 to 0.1 Im) can act as condensation nuclei to facilitate the condensation of water vapor, thus promoting the formation of fog and ground mist. Particles less than 2 or 3 [Lm in size (about half by weight of the particles suspended in urban air) can penetrate the mucous membrane and attract and convey harmful chemicals such as sulfur dioxide. In order to address the special concerns related to the effects of very fine, iuhalable particulates, EPA replaced its ambient air standards for total suspended particulates (TSP) with standards for particlute matter less than 10 [Lm in size (PM, ). 

Although it is entirely possible for erosion-corrosion to occur in the absence of entrained particulate, it is common to find erosion-corrosion accelerated by a dilute dispersion of fine particulate matter (sand, silt, gas bubbles) entrained in the fluid. The character of the particulate, and even the fluid itself, substantially influences the effect. Eight major characteristics are influential particle shape, particle size, particle density, particle hardness, particle size distribution, angle of impact, impact velocity, and fluid viscosity. 

Much of the concern about particulate matter in the atmosphere arises because particles of certain size ranges can be inhaled and retained by the human respiratory system. There is also concern because particulate matter in the atmosphere absorbs and scatters incoming solar radiation. For a detailed discussion of the human respiratory system and the defenses it provides against exposure of the lungs to particulate matter, see Chapter 7. 

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. 

Because there has been no recent analysis of the relationship between the concentration of total suspended particulate matter in the air of cities with populations of different sizes, we are forced to use data for the decade... 

The industries which produce and handle various stone products emit considerable amounts of particulate matter at every stage of the operation. These particulates may include fine mineral dusts of a size to cause damage to the lungs. The threshold values for such dusts have been set quite low to prevent disabling diseases for the worker. 

The three major characteristics of particulate pollutants in the ambient atmosphere are total mass concentration, size distribution, and chemical composition. In the United States, the PM q concentration, particulate matter with an aerodynamic diameter <10 /nm, is the quantity measured for an air quality standard to protect human health from effects caused by inhalation of suspended particulate matter. As shown in Chapter 7, the size distribution of particulate pollutants is very important in understanding... 

Fig. 14-6. Schematic diagram of a four-stage cascade impactor. Source Giever, P. M., Particulate matter sampling and sizing, in "Air Pollution," 3rd ed., Vol. lil (A. C. Stem, ed.). Academic Press, New York, 1976, p. 41,...

The concentration of indoor pollutants is a function of removal processes such as dilution, filtration, and destruction. Dilution is a function of the air exchange rate and the ambient air quality. Gases and particulate matter may also be removed from indoor air by deposition on surfaces. Filtration systems are part of many ventilahon systems. As air is circulated by the air-conditioning system it passes through a filter which can remove some of the particulate matter. The removal efficiency depends on particle size. In addition, some reactive gases like NOj and SOj are readily adsorbed on interior surfaces of a building or home. 

The most common monitoring of particulate matter is for light attenuation (opacity). Less frequently used methods exist for monitoring mass concentration, size distribution, and 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. 

The particles most likely to cause adverse health effects are the fine particulates, in particular, particles smaller than 10 p and 2.5 mm in aerodynamic diameter, respectively. They are sampled using (a) a high-volume sampler with a size-selective inlet using a quartz filter or (b) a dichotomous sampler that operates at a slower flow rate, separating on a Teflon filter particles smaller than 2.5 mm and sizes between 2.5 mm and 10 mm. No generally accepted conversion method exists between TSP and PM,o, which may constitute between 40% and 70% of TSP. In 1987, the USEPA switched its air quality standards from TSP to PMk,. PM,q standards have also been adopted in, for example, Brazil, Japan, and the Philippines. In light of the emerging evidence on the health impacts of fine particulates, the USEPA has proposed that U.S. ambient standards for airborne particulates be defined in terms of fine particulate matter. 

List several types of air cleaning devices that can be used to remove airborne particulate matter. Rank these in order of their collection efficiency and typical maximum size particle capture. 

The term fluid applies to both liquids and gases, including liquids and gases containing particulate matter of various sizes. 

Fumes Small solid particulate matter normally spherical in shape and ranging in size from 0.001 to 1 xni. 

Particle size distribution A method of relating the size or weight of particulate matter, e.g., 50% with diameters in the... 

Particulate matter Matter consisting of particulate liquid and solid substances ranging in size from 0.0002 pm to 500 pm in diameter. 

Respirable particles Particulate matter of such a size that it can pass through the body defences and into the lungs, where, depending on its nature, it will either deposit itself or be exhaled. 

Sieving The use of sieves for the collecting of particulate matter or for the grading by size of particulate matter for classification purposes. 

All comhustion processes produce particulate matter. Amounts and size distribution of the particulates emitted depend on a number of factors, including fuel burned, type ofboiler, and effectiveness of collection devices. 

The first method used for wear particle analysis is routine monitoring and trending of the solids content of machine lubricant. In simple terms the quantity, composition and size of particulate matter in the lubricating oil is indicative of the mechanical condition of the machine. A normal machine will contain low levels of solids with a size less than 10 microns. As the machine s condition degrades, the number and size of particulate matter will increase. 

---