Sampling Aerosol By In Situ Versus Standard Methods: Some Results From Recent Experiments And Developmental Work

Recent work comparing results of sampling aerosol through ductwork, with impactors, and by other standard methods versus in situ methods are presented for three aerosol environments: Airborne measurements of atmospheric aerosol, at high temperatures inside a smoke stack, and in a laboratory environment at very high concentrations. The airborne work involves the comparison of particle size distributions measured by an in situ sizing instrument inside a wind tunnel with that obtained through ductwork using an isokinetic intake. The results show a sharp decrease in particle numbers measured in the ductwork at sizes above a few microns, in all cases, with negligible losses in the submicron range. A water cooled in-stack particle size spectrometer is being developed for the EPA. In situ measured size distributions will be compared to impactor samples and integrated extinction coefficients with transmissometer opacity values. A high concentration in situ measuring laboratory instrument is described which can perform measurements in the 0.3 to 6.0 µm size range at concentrations up to 107cm-3 without dilution.