ARB Research Seminar
This page updated July 25, 2013
A Low-Cost, Ultra-Fine Particle Concentration Monitor
Susanne V. Hering, Ph.D., President, Aerosol Dynamics Inc.
September 08, 2006
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA
Ultra-fine particles have been associated with adverse health risks, yet their concentrations in occupied spaces are not well known. Levels in homes, offices and schools are influenced by both indoor and outdoor sources, as well as building ventilation and proximity to roadways. Monitoring of these micro-environments where people spend the majority of their time is important in the assessment of community exposures.
For the last thirty years, ultra-fine particle number concentrations have been measured using butanol-based condensation particle counters. For reasons of odor and toxicity, these monitors are not suitable for measurement in occupied spaces. In 2003 a new, water-based "growth tube" technology was introduced to enable ultra-fine particle measurement without using toxic substances. In 2005 this technology was adapted to a portable, micro-environmental monitor for ultra-fine particles. This micro-environmental, water-based condensation particle counter (ME-WCPC) has a lower size limit of 6 nm, a sampling rate of 0.12 L/min, and a passive water feed system. It is a 12-volt instrument, weighing 2.5 kg, with on-line data logging capability, and one-week unattended operation.
Reported here is the evaluation of the ME-WCPC under field conditions. Comparison is made to three types of butanol-based counters: TSI Models 3010, 3022 and 3025. Ambient sampling was done in Riverside and Berkeley, CA. Residential measurements were made at two homes, including one kitchen. Direct assessment of automotive emissions was made through measurements from the air duct of the Caldecott Freeway Tunnel. At all locations the collocated ME-WCPCs agreed with each other, with the square of the correlation coefficient above 0.97 and slopes near 1. For particle number concentrations below 200,000 cm-3, measurements from the ME-WCPC are within a few percent of those from the butaonol-based TSI-3022, and higher than those from the dilution-corrected TSI-3010, consistent with the differences in the lower particle size limits cutpoints of the instruments (7 nm for the TSI-3022, 10 nm for the TSI-3010). Differences among all instruments are observed at concentrations above 200,000 cm-3.
Susanne V. Hering, Ph.D., is the President of Aerosol Dynamics Inc., a company she founded in 1991 to pursue advancements in airborne particle measurements. Her company has developed several ambient aerosol monitoring instruments, including a laminar flow water-based condensation counter for ultrafine particles. Current activities include development of an aerosol GC-Mass Spectrometry system for the in-situ quantification of organic marker compounds, and an aerosol interface with laboratory-on-a-chip technology for the assay of inorganic ions in atmospheric aerosols. Dr. Hering received her PhD in Physics from the University of Washington in 1974, and completed postdoctoral studies in atmospheric aerosols at Caltech. She served as editor of the seventh edition of Air Sampling Instruments, a reference book published by the American Conference of Governmental Industrial Hygienists. She has been an active member of the American Association for Aerosol Research, serving 10 years on the Board, and twice as President.