Aerosol Mobility Imager for Rapid Size Distribution Measurement

Atmospheric aerosols influence the earths radiation balance through direct scattering and absorption of radiation, and through alteration in the formation, brightness and extent of clouds. The concentrations and size distribution of aerosols aloft is important to these effects. Needed is a method to capture the size-resolved vertical profiles of those particles in the 10 600 nm size range that dominate the numbers of particles that are, or grow to become cloud condensation nuclei. Obtaining such data with finer spatial resolution requires rapid measurements, with averaging times of the order of one second or less. In collaboration with Brookhaven National Laboratory, Aerosol Dynamics will develop a mobility imaging system to provide complete size distributions for particles between 10 and 600 nm in diameter, with a time resolution of 1-10Hz. The instrument will be suitable for aircraft measurements, and will be available for use by DOE field campaign by spring 2014. This instrument combines two technologies, a two dimensional electrical mobility separator, and a laminar flow water condensation. Particles are separated spatially, enlarged through water condensation, and imaged onto a CCD array that instantly record their positions and number concentrations. This instrument enable the rapid measurement of ultrafine particle size distributions that is critically needed for measurements aloft, and for studies such as flow chambers or plume studies where particle concentrations change rapidly. The Phase I project achieved each of its objectives. A one-dimensional mobility separator and water condensation system provided clear separation of particles by size, with 1006% capture of particles between 10 nm and 100 nm in diameter. Data capture was 10Hz, and sizing and concentration was comparable to a 0.01Hz scanning mobility sizing system. These results demonstrate the feasibility of the approach. The Phase II project will extend the size range of the instrument through the adoption of a two-dimensional mobility separator, will optimize and characterize its performance over a range of operating temperatures, relative humidity values and altitudes, and will demonstrate the unit the field. The initial market for this instrument will be university and government research groups in the fields of atmospheric science, nanoparticle fabrication and pharmacology. Downstream markets will expand to industrial process monitoring, pharmacological testing and industrial hygiene.