10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
A Compact, Battery-Operable, Dual-Channel, Water-Based Condensation Particle Counter
SUSANNE HERING, Gregory Lewis, David Workman, Aerosol Dynamics Inc.
Abstract Number: 995 Working Group: Instrumentation
Abstract A compact, dual-channel, water-based condensation particle counter is being developed to provide simultaneous measurements of ultrafine particle concentrations in two separate flow streams. The reported parameters are the airborne number concentration of ultrafine and fine particles in each channel of the system. The size range of detected particles extends from 7 nm to several micrometers in diameter. The time resolution is 1 second. Envisioned applications encompass those requiring simultaneous measurements in multiple size fractions, or in two distinct physical spaces. The long term goal is a battery powered instrument that is wearable.
As with other condensation particle counters, this system relies on condensational enlargement to grow ultrafine particles to optically detectable sizes. Yet in contrast to those now available, the instrument being developed here provides the following advantages: (1) it uses water, rather than alcohol, for the condensational enlargement; (2) it can be operated in any orientation; (3) it tolerates tipping and jostling; (4) it detects particles as small as 7 nm in diameter and (5) it is compact.
The approach is a self-sustaining water-based condensational growth system commonly referred to as “MAGIC” (moderated aerosol growth with internal water cycling). The MAGIC technology captures water vapor internally, allowing sustained operation without need of on-board reservoirs. The growth tube of the MAGIC system has a continuous water-wetted wick that spans three temperature regions, the middle one of which is warmer than the other two. Water evaporation from the warmed, middle section provides the water vapor that creates the supersaturation for particle activation and growth. The cooler, downstream section captures this water vapor, while maintaining supersaturated conditions needed for droplet growth. Capillary action transports the water captured by this stage, and by the initial stage, back to the warmed mid-section, providing sustained operation. MAGIC has no liquid reservoirs, and thus is insensitive to orientation and motion.
For the dual-channel device presented here, two identical MAGIC growth tube channels are used, both operated at a sample air flow of 100cm3/min. A common set of temperature controls ensures that the respective stages of each channel are operated at the same temperatures. Each growth channel is coupled to an independent optical detector which detects individual droplets to enumerate the number of concentration of condensationally enlarged particles. The optical detectors are newly developed and miniaturized to provide a compact system. The dual-channel growth tube and optics, excluding electronics and supporting components, measures approximately 6cm x 10cm x 10cm.
Laboratory evaluations have been conducted under a variety of temperature and relative humidity conditions. Testing with monodispersed aerosols has demonstrated a lower particle size limit of detection of 7nm for both sucrose and sulfate aerosols. The response is linear to the highest concentrations tested of 8x104/cm3. For sampling ambient air, the standard deviation between the two channels was 2%.