10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Real-time QCM MOUDI for Ambient Aerosol Monitoring
MODI CHEN, Francisco Romay, Robert Anderson, H. Dirk Felton, TSI Incorporated
Abstract Number: 1614 Working Group: Instrumentation
Abstract The recently developed Real Time QCM (Quartz Crystal Microbalance) MOUDI (TSI Model 140) was evaluated at the Queens College air sampling station operated by the New York State Department of Environmental Conservation. This evaluation started in December, 2017. Ambient air was sampled from the roof of the site through a PM10 inlet into the instrument at a flow rate of 10 L/min. The temperature inside the sampling site, where the QCM MOUDI was located, was conditioned and maintained at 24 °C. The RH conditioner of the QCM MOUDI had a control set point of 65 %. Therefore, the ambient aerosol sampled by the QCM MOUD was always maintained at 24 °C and 65 % RH, regardless of the outdoor temperature and RH. The performance of the QCM MOUDI was very stable even during the days when the outdoor air temperature was below -10 °C.
The initial data collected during the first two months of measurements was compared with results from a Tapered Element Oscillating Microbalance (TEOM Model 1405 DF) for PM2.5 mass concentrations, and with results from a TSI 3783 water CPC, which measures the total particle number concentration of particles larger than 7 nm. The QCM MOUDI collected particles between 45 nm and 2.5 μm in six size fractions with 15 min time resolution. The total mass collected on all the QCM stages was converted to the PM2.5 mass concentration and was compared with the hourly PM2.5 values measured by the TEOM. The TEOM data showed very abrupt changes from hour to hour. When ambient particle concentration was low, the TEOM sometimes showed negative PM2.5 values for hours. PM2.5 values measured by QCM MOUDI showed less abrupt changes over time, and seemed to report very reasonable PM2.5 values as low as 3 μg/m3. The CPC number concentration data was also compared with the QCM MOUDI to check the overall time trends. PM2.5 measured by both QCM MOUDI and TEOM followed similar trends when compared to the total particle concentration reported by the CPC most of the time. The QCM MOUDI data was further compared with daily FRM filter measurements to confirm its accuracy. These preliminary results show that QCM MOUDI has higher time resolution than the TEOM. It is also suitable for measuring the size resolved mass concentration of PM2.5 even at very low particle concentration levels.