ABSTRACT
CONTENTS Introduction .....................................................................................................................41 Generation ........................................................................................................................47 Dispersion .........................................................................................................................47 Sampling and Characterization ........................................................................................ 49 References ........................................................................................................................ 50 Bibliography .................................................................................................................... 50
Introduction One cubic centimeter of atmospheric air contains approximately 2.5 × 1019 molecules. About 1000 of these molecules may be charged (ions). e molecules of N2, O2, and the various trace gases have sizes (diameters) of about 3 × 10−8 cm. e average distance between the molecules is about ten times the molecular size. In addition to the molecules and the ions, 1 cm3 of air also contains a substantial number of particles varying in size from a few times the molecular size to several microns (μm, 1 μm = 10−4 cm). In relatively clean air, there are about 1000 particles with diameters 0.001-50.0 μm while in polluted air there can be 100,000 or more, including pollen, bacteria, dust, and industrial emissions. ese particles, which can be both benefi cial and detrimental, arise from a number of natural sources as well as from the activities of the earth’s inhabitants. e particles can have complex chemical compositions and morphologies, and may even be radioactive or toxic. A suspension of particles in a gas is known as an aerosol. Atmospheric aerosol is of global interest and has an important impact on our lives.
