A Miniature Collector for Time-Resolved Aerosol Chemistry

ALEX TENG (1), Gregory Lewis (1) and Susanne Hering (1)

(1) Aerosol Dynamics Inc., Berkeley, CA

     Abstract Number: 423
     Last modified: November 13, 2009

Abstract
Time- and chemically- resolved data on fine, airborne particles are important for understanding particle sources, their effects on human health and their role in global climate. Especially important for epidemiology studies are complete data sets, with consistent, daily measurements. Also needed are compact, battery-powered instruments that can serve as personal monitors for time-resolved aerosol chemistry.

Utilizing the condensation technology of our water-based condensation particle counters, we have developed a miniature, sequential fine particle collector. Particles are activated and grown through water condensation in a laminar, differentially diffusive flow. Once grown, they are collected within a 30 µL well by means of impaction. Multiple wells are used to provide time-resolved, sequential samples. The instrument is 150mm long, weighs 400 g and requires 2Watts. To date it is capable of 8 sequential sample collections. We are working to interface with an ion chromatograph to automate the extraction, injection and data reduction of the samples.

With the laminar flow condensation approach, nanometer-sized particles are enlarged through water condensation to form 2-µm droplets that are readily collected. The droplets formed are uniform in diameter, independent of the input particle size, and nearly independent of input concentration. The supersaturation required for condensational growth is created by means of the differential rates of sensible heat and water vapor transport as a cool flow is introduced into a warm, wet-walled tube. Typically, this temperature differential is 25°C, enabling the capture of nanometer-sized particles without steam or temperature extremes. Once enlarged, the particles are deposited by impaction. The lower particle size cutpoint is 8-10nm, with greater than 95% collection for all particles above 20nm. The collector is efficient for both hydrophilic and hydrophobic particles, and collection efficiency remain high at the highest particle concentration tested of 10^5cm-3. Side-by-side comparisons with filter samples show equivalency for both sulfate and nitrate in ambient air, and for laboratory generated ammonium sulfate and ammonium nitrate.