ABSTRACT
Time-integrated samples obtained by the type of instruments described in Chapter 12 are usually sufficient in most cases. However, it is sometimes necessary to obtain measurements rapidly to estimate hazard levels or to evaluate control systems. Such measurements can also help in determining how the time-integrated measurements can be obtained optimally to provide the most useful information. Direct reading instruments can be used to determine a variety of aerosol properties. In some cases, the inertial properties of the aerosol are relevant, and hence it becomes important to measure the particle aerodynamic diameter. The mass concentration of a healthrelevant aerosol fraction is clearly of interest, and hence several instruments have been developed for such measurements. In recent years, the surface area concentration and the number concentration of aerosol particles have also been thought to be relevant to human exposures that can cause health effects.
