Instantaneous Aerosol Mobility Sizing

The concentration and size of atmospheric particles are critical to assessing their effects on human health and on Earthĺs climate. Particle size is especially important as it affects particle transport in the atmosphere, patterns of deposition in the lung, aerosol cloud interactions, and dynamics of key aerosol processes such as new particle formation. DOE specifically points to the need for an affordable means of characterizing airborne particle size distributions in urban environments. The ôAerosol Mobility Imagingö (AMI) system of this project provides nearly instantaneous aerosol size distributions in the critical8-400 nm size range, which cannot be probed by optical methods. AMI uses a parallel plate mobility separator coupled to an extraction growth cell and imaging system. Airborne particles are spatially separated in accordance with their electrical mobility, and those closest to the high voltage electrode are extracted, condensationally enlarged along their flow trajectories, and imaged. By using a parallel plate separator with a complex electrode, we can vary the size of the extracted particles across the extraction slit, such that the complete size spectrum is captured in each image. No scanning is required. The time response of the system is controlled by aerosol transport in the flow lines and is of the order of 1-2s. Through our Phase I efforts we have addressed key feasibility questions. We showed that particles at the exit of a parallel plate mobility separator can be extracted, focused, condensationally enlarged, and imaged while maintaining their relative positions. We demonstrated that a single image can capture a complete particle size distribution from fifteen nanometers to a few hundred nanometers. We demonstrated the capability of a bipolar separator for simultaneous classification of positively and negatively charged particles. The Phase II effort will produce a validated, integrated system for rapid ambient aerosol size distribution measurements in the diameter range of 8-400nm, including assessment of measurement precision, and accuracy Component design will be optimized using numerical modeling tools and mechanical design will aim for a fully integrated design of the components. Laboratory validation tests will be conducted with size-selected aerosols. Transfer functions will be characterized and data analysis tools will be developed. System validation also includes side-by-side tests against more traditional methods while sampling ambient air. Commercial applications span a wide range of industrial and laboratory research uses for which rapid measurements of aerosol size distributions are needed. The AMI system could potentially replace many scanning mobility particle sizing systems, which have become standard aerosol equipment in laboratories and industry.