Automobile catalytic converters have been used for 30 years to greatly reduce air pollution worldwide, but small amounts of their metals have been detected in air, soil, plants, and waterway sediments. Now, elevated levels of metals emitted from catalytic converters have been measured at busy street intersections in Boston in the first major U.S. study of catalyst metals in urban aerosols (Environ. Sci. Technol. 2005, 39, 9464). Sebastien Rauch of Chalmers University of Technology, in Sweden, and coworkers used air filters to trap micrometer-sized particles containing the metals and analyzed the samples by inductively coupled plasma mass spectrometry. Average measured concentrations in Boston of platinum, palladium, rhodium, and osmium range from 0.07 to 8.1 pg/m3. These are not yet considered high enough to pose a serious health risk, but they indicate an emerging problem, given that the number of vehicles worldwide is expected to more than double in the next few decades, the researchers note. Established occupational exposure limits of the metals are 1–2 μg/m3.