The development of a robust microwave-assisted acid digestion procedure followed by inductively coupled plasma-MS (ICP-MS) was presented to quantify rare earth elements (REE) in FCC catalysts and atmospheric fine particulate matter (PM2.5). At 200°C, 200 psig, acid digestion with 20 min dwell time effectively solubilized REE from six fresh catalysts, a spent catalyst, and PM2.5. This method was employed to measure 27 non-REE including Na, Mg, Al, Si, K, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Zr, Mo, Cd, Cs, Ba, Pb, and U. The method developed for FCC catalysts was successfully implemented to measure trace to ultra-trace concentrations of La, Ce, Pr, Nd, Sm, Gd, Eu, and Dy in ambient PM2.5 in an industrial area of Houston, TX. The results from apportionment of fine particulate matter levels at four air sampling stations in the Houston, TX, area to quantify the impact of emissions from a local refinery during a reported emission event were presented. This is an abstract of a paper presented at the AIChE Annual Meeting (Salt Lake City, UT 11/4-9/2007).