fails to exit with the expired air. Thus, the dose is directly proportional to three variables: ventilation, pollutant concentration, and the fraction deposited.
First, consider ventilation . The standard 70-kg adult at rest breathes about 7.5 L/min (International Commission on Radiological Protection, 1975). However, a value of 20 L/min would be more appropriate for adults in indoor environments who periodically stand, walk, type, or perform other modest tasks. During heavy exercise, ventilation can increase by a factor of as much as 10, to exceed 100 L/min (International Commission on Radiological Protection, 1975).
For particles, collection efficiency (CE) is determined primarily by two factors: particle size and breathing pattern. If the geometric size, shape, and density of the individual particles or droplets are known, then the distribution of particle diameters can be described. Because it is a better predictor of the behavior of the particle in the respiratory tract, aerodynamic diameter rather than optical measurement is used to express the range of particle sizes. Aerodynamic diameter is defined as the diameter of a sphere of unit density that has the same settling velocity as the particle being measured. It may be expressed as the count median aerodynamic diameter (CMAD) or mass median aerodynamic diameter (MMAD). These are, respectively, the diameters for which half of the number (or mass) of the particles are less than that diameter and for which half exceed it.
The particles in mainstream cigarette smoke have been measured by several investigators using a variety of analytical devices. Because of the different apparatus and methods of smoke generation and dilution, results vary. However, to an order of magnitude, the findings are reasonably consistent. McCusker et al. (1983) used a device called the single particle aerodynamic relaxation time (SPART) analyzer to size mainstream particles from several brands of cigarettes, with and without filters. The MMAD for all brands averaged approximately 0.46 mm and was not markedly