Abstract: An apparatus and method for detecting medium and high atomic weight eleme includes a sampling mechanism for removing particles of an element to be detected from the aerosol and confining the particles to a selected geometry. The aerosol may, for example, be pumped through a filter with the particles being confined on a defined area of the filter. The selected geometry is then irradiated with x-rays to cause the particles to fluoresce and produce secondary x-rays. The secondary x-rays are detected and analyzed using criteria which determine the identity and concentration of the particles in the selected geometry. The air stream of the aerosol through the filter can be measured to determine the volume of aerosol from which the particles were removed as an aid in determining concentration.