An in-stack cascade impactor was used to determine the size distribution of particles, before and after emission control systems, of a coal-fired power plant, a steel plant, and a cotton gin. Samples were analyzed for total particulate matter and elemental metal content by graphite-furnace atomic absorption; Se was analyzed by neutron activation. A sharp decrease in the concentration and particle size was observed after the particulates passed through the control systems. Pronounced metal concentration and particle size relationships were found in the power plant and steel plant samples. The power plant outlet samples showed an increased concentration of Cr, Pb, Sb, Zn, and Se in the particle size range of 0-1 pm diameter. The particle removal efficiency of the baghouse and electrostatic precipitator control devices in this study was a t least 98% for submicrometer sized particles.Stationary emission sources can contribute significantly to the amount of primary particulate matter in air of anthropogenic origin, especially trace metals ( I , 2 ) . The effectiveness of particle control devices depends in large measure on the particle size of stack aerosols, yet, very little published information is available on the size distribution of particulates associated with stationary sources (3, 4). Particle size fractionating devices which can operate in a harsh stack environment have become available and should lead to a better understanding of particulate emissions (5-7). By applying methods similar to those used in determining the weight-size distribution of particles suspended in ambient air ( 8 ) , we have used a Pilat impactor ( 5 ) to determine the weight size distribution of total particulate matter and trace metal components in several stationary emission sources. Samples were collected both before and after the emission control devices to assess the aerosol removal efficiency. The sources tested included a coal-fired power plant equipped with an electrostatic precipitator, a cotton gin equipped with a wet scrubber, and an electric arc furnace ferro plant equipped with a baghouse control system. These studies were carried out as part of a source testing program on best controlled industries for developing emission standards on new stationary sources. Experimental MethodsDescription of the Cascade Impactor. A University of Washington Mark I11 source test cascade impactor was used aerodynamically to size and collect aerosols within stacks of selected stationary sources (9). The impactor consists of seven stages and a backup filter to collect unimpacted particles, all of which are housed in a stainless steel cylinder that can be inserted into a stack or duct through a 10.2-cm (4-in.) port. The Mark I11 version differs somewhat from previous designs (5, 1 0 ) in that the airstream passes through the center of "donut" shaped collection surfaces rather than around openings near the walls to minimize wall losses. The sampler fractionates particles in the size range of about 50-0.5-wm diameter, expressed as spheres of uni...