Section V - Sampling, Monitoring and Measuring of Fine Particulate Air Pollutants

Abstract

This chapter discusses the ways of sampling, monitoring, and measuring of fine particulate air pollutants. In a gas flow, the usual definition of particle size is the aerodynamic equivalent diameter. The aerodynamic equivalent diameter is the diameter of a spherical particle with a density of 1 gcm-3 that falls at the same rate as the particle. The Stokes particle diameter is the diameter of a sphere of equivalent uniform density that falls at the same speed as the particle. Some instruments such as the impactor, spiral centrifuges, and multiple cyclones measure aerodynamic diameter directly. Other indirect methods must be calibrated in terms of aerodynamic diameter. Indirect methods define a particle size that is based on some physical or chemical property of the particle other than its aerodynamic size. The electric-mobility analyzer classifies particles according to an equivalent drift velocity diameter. Optical counters measure the light-scattering area of a particle. The data obtained from these and other indirect analyzers must be transformed to obtain the aerodynamic equivalent diameter. The transformation requires knowledge of other particle properties that might not be available or easily measured.