The FOREWORD of aerosols has found wide popularity in most life styles of our population. Toxic aerosols present special problems which require accurate measurement of airborne particles and droplets so that their effect on health can be evaluated. Meaningful monitoring of aerosol particles usually must be performed in real time and at the site of exposure. Rigorous and exacting measurement conditions must be met. Thus, new and innovative methods and instrumentation are being developed to meet the rigorous monitoring criteria necessary to safeguard health. The dramatic increase in the number of food, drug and cosmetic products now consumed as aerosol spray products coupled with their measurement needs have prompted the Food and Drug Administration and the National Bureau of Standards to co-sponsor this Seminar on Aerosol Measurements to better define the needs and to stimulate the development of new methodology for making rapid and reliable aerosol measurements. Philip D. LaFleur, Acting Chief PREFACE in This seminar was organized to provide provide an opportunity for representatives of instrument manufacturers, research groups and government agencies to evaluate the latest developments instrumentation for making rapid measurements on aerosols. The incentive behind this effort is the realization that the popular uses of aerosols and the accompanying exposures are rapidly rising in frequency and importance. Over two billion spray cans are used each year to apply paints, insecticides, deodorants, oven cleaners and a host of other useful but toxic materials. The need to maintain quality control in spray applications and to monitor any potential hazards demands ability to measure aerosol particles accurately and reproducibly. an The particle sizes and concentrations encountered in aerosol sprays place such unusual demands on the measuring techniques that conventional instruments appear limited in their ability to provide the required dynamic range, resolution and accuracy. This workshop was directed, therefore, to a discussion of a representative selection of the newer aerosol instruments that are under development or have been completed recently. It is hoped that these proceedings will serve both to illustrate some of the latest approaches to aerosol instrument design and to stimulate the development of additional new concepts in the future. Wayne A. Cassatt, Coordinator SUMMARY The papers recorded in these proceedings describe several aerosol measuring instruments based upon a variety of operating principles. The physical phenomenon underlying these principles include laser light scattering, optical imaging, Doppler shift, electromobility, piezoelectric effect, and beta-ray absorption. Two review papers are included which describe several other phenomena upon which measurements based. Instruments designed around the first three principles have capabilities for detecting and sizing indivdual aerosol particles, but they have definite limitations regarding the concentrations and count rates that they can handle. Instruments based upon the latter three principles are much more adept at handling high concentrations but it is difficult, if not impossible, to detect and to size individual particles with them. Obviously, the principle to be employed and the specific design of the final instrument will depend upon the measurement requirements to be met. Those devices that rely upon the interaction between light and individual particles can be quite different in basic design and performance. Some measure intensity at one or two selected angles, others analyze the intensity pattern over large solid angles, and still others measure focused optical images. In all, some eight different instruments of this type were discussed here. In order to compare these instruments and their performances in a convenient fashion, they have been listed along with their specifications in table 1. This is by no means intended to be a complete list of the aerosol instruments on the market or under construction in various laboratories around the country. Rather, it is meant to be indicative of the state of the development in this field. Discussions among seminar attendees revealed that many questions remain to be answered before the more difficult aerosol measurement problems can be solved. For example, in the analysis of very dense aerosols questions arise concerning coincidence losses or agglomeration effects that may result from collisions between particles as they are drawn into the measuring volume. Volatilization or condensation effects may alter the size distribution if the measurements are made late in time. the lack of size resolution or sensitivity may prevent the detection of useful information. In some cases the lack of instrument portability or the length of time required for data processing may constitute serious handicaps. Finally, variations in particle shape or index of refraction can alter the instrument response and cause difficulties in interpretation. The developers of the instruments described in this seminar have quite successfully attacked and solved one or more of these problems with respect to aerosol spray measurements. On the other hand, it would appear that much remains to be done to produce an optimum device, especially if it is to be useful for general applications under a variety of conditions. Wayne A. Cassatt, Coordinator |