These data can be presented in a histogram with the area of each bar representing the proportion of particles in that size bin, usually normalised by dividing the number of particles in a bin by the width of the interval so that the area of each bar is proportionate to the number of particles in the size range that it represents. Another approach splits the size range into intervals and finds the number (or proportion) of particles in each interval. However, this approach proves tedious to ascertain in aerosols with millions of particles and awkward to use. One approach to defining the particle size distribution uses a list of the sizes of every particle in a sample.
This distribution defines the relative amounts of particles, sorted according to size. However, more complicated particle-size distributions describe the sizes of the particles in a polydisperse aerosol. Each distribution is normalized so that the total area is 1000.įor a monodisperse aerosol, a single number-the particle diameter-suffices to describe the size of the particles. diameter distribution, a surface area vs. The same hypothetical log-normal aerosol distribution plotted, from top to bottom, as a number vs. Also commonly used is the aerodynamic diameter, d a. The equivalent volume diameter ( d e) is defined as the diameter of a sphere of the same volume as that of the irregular particle. The equivalent diameter is the diameter of a spherical particle with the same value of some physical property as the irregular particle.
Liquid droplets are almost always nearly spherical, but scientists use an equivalent diameter to characterize the properties of various shapes of solid particles, some very irregular. Most aerosols, however, as polydisperse colloidal systems, exhibit a range of particle sizes. A monodisperse aerosol, producible in the laboratory, contains particles of uniform size. Particle size has a major influence on particle properties, and the aerosol particle radius or diameter ( d p) is a key property used to characterise aerosols.Īerosols vary in their dispersity. Also commonly used is the number concentration ( N), the number of particles per unit volume, in units such as number per m 3 or number per cm 3. Environmental science and environmental health often use the mass concentration ( M), defined as the mass of particulate matter per unit volume, in units such as μg/m 3. There are several measures of aerosol concentration. Various types of aerosol, classified according to physical form and how they were generated, include dust, fume, mist, smoke and fog.
Key aerosol groups include sulfates, organic carbon, black carbon, nitrates, mineral dust, and sea salt, they usually clump together to form a complex mixture. Primary aerosols contain particles introduced directly into the gas secondary aerosols form through gas-to-particle conversion. This term developed analogously to the term hydrosol, a colloid system with water as the dispersed medium. Donnan presumably first used the term aerosol during World War I to describe an aero- solution, clouds of microscopic particles in air. Meteorologists usually refer them as particle matter - PM2.5 or PM10, depending on their size. An aerosol includes both the particles and the suspending gas, which is usually air. Most of the particles in this aerosol are nearly spherical.Īerosol is defined as a suspension system of solid or liquid particles in a gas. Photomicrograph made with a Scanning Electron Microscope (SEM): Fly ash particles at 2,000× magnification.
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