A Pulsed Condensation Particle Counter for Community Monitoring

SUSANNE HERING, Gregory S. Lewis, Steven Spielman, David Pariseau, Aerosol Dynamics Inc.

     Abstract Number: 13
     Working Group: Instrumentation and Methods

Abstract
As community monitoring of air pollutants becomes ever more widespread, it is important to develop instrumentation that can provide accurate and reliable data at a reasonable cost. Especially challenging is the monitoring of ultrafine or nanometer sized particles, as they are too small to be detected directly by optical sensors currently used for community monitoring. Reported here is a new type of condensation particle counter that targets this community measurement need. Referred to as the Pulsed Condensation Particle Counter (PCPC), this new instrument utilizes an quasi-adiabatic expansion coupled to single particle counting to monitor particle number concentrations in the 5-2000 nm size range. The PCPC introduces aerosol sample through an inlet valve into a Nafion-walled chamber surrounded by a water jacket. After a brief pause to allow for humidification, and with the inlet valve closed, a portion of the sample is extracted through an optical counter (Particles Plus LLC,. Stoughton MA). The resulting expansion creates a region of supersaturation leading to the condensational growth of the particles within the cell. The resulting droplets are individually counted as they exit the cell. The sample volume is determined from the change in pressure in the chamber during the expansion. This yields a 'first principles' measurement of ultrafine particle concentrations.

The particle size dependent detection efficiency was measured using monodispersed particles generated through electrical mobility classification with prototype for the TSI 3789 serving as reference. The PCPC detects particles as small as 5nm, with counting efficiencies above 80% for particles larger than 10nm, and above 95% for particles above 30nm. Ambient monitoring alongside a water-based condensation particle counter gives with a 5nm threshold yield regression slope above 0.9, and a correlation coefficient squared of 0.98.

This work was supported by NIEH under Grant number R44-ES031458, and through in-kind support from Particles Plus Inc.