Because of rapid change in both their chemical and physical properties, concentrated (0.5 to 100 g/m³) aerosols, such as a diesel fuel-based military obscurant and tobacco smoke, represent a unique challenge to the analytical chemist. Sampling procedures must minize the alteration of phase concentrations of particular constituents. For example, collection of tobacco smoke particulate matter on glass fiber filters is limited to linear velocities of ∼100 cm/min to prevent evaporation of nicotine. Trapping of reactive constituents must be performed rapidly so as to prevent loss through side reactions with other smoke constituents.

Chemical characterization studies are directed at comparing laboratory generated test aerosols with those existing under field or “real world” conditions. For the diesel fuel aerosol, a tiered analytical scheme, high-performance liquid chromatographic (HPLC) fractionation followed by high resolution gas chromatography, has proved useful for the determination of major constituents. Limited comparisons have suggested that observed differences result from differences in fuel composition and sampling conditions, rather than generation procedures. For tobacco smoke, comparisons are made between the composition of smokes generated under standard conditions by smoking machines and that of smokes to which animals are actually exposed. In some cases, exposure smokes have been found to be depleted in particulate matter, relative to the vapor phase. However, gross changes in the composition of the particulate matter do not occur.

On-line instrumental monitoring of smoke concentrations provides an important adjunct to chemical measurements. An optical particle monitor measures back-scattered infrared radiation as being proportional to smoke concentration. Systems employing the particle sensor are being used now to quantitatively determine particle concentrations in tobacco smoke and diesel fuel aerosol inhalation toxicology studies.