Instantaneous Aerosol Mobility Sizing

With its Urban Integrated Field Laboratories research effort, DOE seeks affordable methods to characterize the urban atmosphere with high time and high spatial resolution. Aerosol size distributions are specifically named by DOE as a parameter that cannot be affordably monitored with currently available methods. The size and concentration of sub-micrometer and ultrafine aerosols are especially critical to evaluating the dynamics of aerosol processes, to identifying sources and origins of new particles and their role in cloud formation, as well evaluating human exposures important to health. Needed are means to map these concentrations with good time and spatial resolution.Vehicle-based platforms, such as instrumented Google street-view cars or mobile monitors, provide air quality data over a large urban environment. However, such ground-based mobile platforms require rapid time response, of the order of one second, as the sampled aerosol is constantly changing. For the critical ultrafine aerosol size range, which cannot be directly measured optically but instead is probed by electrical mobility, the current commercial methods do not have the necessary time resolution. Our approach separates airborne particles spatially in accordance with their electrical mobility, and then counts these particles as a function of their position (and hence size) through condensational growth and optical imaging. The complete size spectrum 10-500 nm size is captured with 10Hz resolution, making feasible accurate measurements on moving platforms.AMI technology uses an innovative approach to facilitate high time resolution measurements within a compact instrument size, representing a significant advance over existing commercially available technologies. Our Phase I project will experimentally evaluate three key components of this approach. First, we experimentally verify the capability of accurately capturing particle positions across the full width of the mobility separator. Second, we will determine the capacity for simultaneous measurement of positive and negative particle mobilities, as this approach has recently been shown to eliminate the need for bipolar ion source. Third, we will evaluate a new concept for the wide-size size range electrode, which has the potential to greatly reduce the required size and cost of the separator. These key steps will allow us in Phase II to design for cost-effective fabrication methods. Through establishing the efficacy of this innovative approach, we aim to provide a compact and affordable instrument for rapid, 1Hz, aerosol size distribution measurement over the critical size range of fine and ultrafine aerosols.Commercial applications span a wide range of industrial and laboratory research uses for which rapid measurements of aerosol size distributions are needed, such as near sources or on mobile platforms. As speed is always desired, our instrument could potentially replace many scanning mobility particle sizing systems, which have become standard aerosol equipment in laboratories and industry.