Inertial collection of fine particles using a high-volume rectangular geometry conventional impactor

This paper presents the development and evaluation of a high-volume rectangular geometry conventional impactor. Operating with a preselective inlet that removes particles larger than 2.5 μm in aerodynamic size, the impactor has been designed to sample ambient fine particles in the accumulation mode range (0.1 < dp < 2.5 μm). Particles are accelerated in a rectangular nozzle, 0.032 cm wide and 28 cm long, and impact on a filter medium attached on a porous glass frit, which is soaked in mineral oil. The impactor operates at a flow rate of 1000 l min−1 with a total pressure drop of 30 kPa. The performance of the slit-nozzle impactor was validated in laboratory and field tests. Laboratory experiments conducted with monodisperse fluorescent PSL particles showed that the aerodynamic diameter of the 50% cutpoint of the impactor is approximately 0.09 μm. Laboratory and field intercomparisons between the high-volume slit impactor and the microrifice uniform deposit impactor (MOUDI) showed that particulate nitrate and sulfate concentrations obtained with the two samples are in good agreement (within 10%). Finally, a comparison between the particulate nitrate concentrations obtained with high-volume impactor and the Harvard/EPA annular denuder system (HEADS) was conducted, using indoor air as the test aerosol. Results from this comparison indicated that losses of nitrate from the impactor are not substantial and range between 5 and 15%. Results from the laboratory and field tests suggest that the high-volume impactor presented in this study constitutes a major improvement in the field of high-volume fine particle sampling.