Static and dynamic light scattering by aerosols in a controlled environment

Abstract

Aerosols are defined as particles suspended in air or any other gaseous medium. These particles may be solid (dust, smoke, fume etc.) or liquid (mist, fog etc.). They range in size from 0.01 micrometers to several tens of micrometers, for example cigarette smoke particles are in the middle of this size range and typical cloud drops are 10 or more micrometers in diameter. Because of their particle nature they are also called “particulate matter” and in literature one often encounters terms like PM2.5 and PM10, which are used for particles smaller than 2.5 micrometers and 10 micrometers respectively. These particles can be classified under two headings: (i) dispersion aerosols, formed by condensation of supersaturated vapor or due to chemical reaction in the gas phase. The particles, which serve as nuclei for condensation are termed as condensation nuclei or cloud condensation nuclei. All aerosol particles are formed either by mechanical processes or by condensation of gases and vapors. Mechanical processes producing aerosols may be natural, like windblown dust, sea salt spray, and volcanoes, or man-made, such as industrial activities, burning of fossil fuels, and the alteration of natural surface cover. The particles produced by mechanical processes in general are coarse with a size of a few micrometers while fine submicrometer particles are formed by condensation. Aerosol particles larger than about 1 micrometer in size are produced by windblown dust and sea salt from sea spray and bursting bubbles.