10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Comparison of the TSI 1-nm and Standard Scanning Mobility Particle Sizers during the Lake Michigan Ozone Study
MEGAN CHRISTIANSEN, Charles Stanier, Sherrie Elzey, Nathan Janechek, Nathan Bryngelson, Maynard Havlicek, Andrea Tiwari, University of Iowa
Abstract Number: 1575 Working Group: Instrumentation
Abstract During the Lake Michigan Ozone Study 2017 (LMOS 2017), the aerosol size distribution was measured for a 1-month period at Zion, Illinois, a site on the Western shore of Lake Michigan. The purpose of the field study was to establish an observational database for improved understanding and model-measurement evaluation of regional and local ozone episodes. Aerosols were monitored as a source apportionment and monitoring site characterization tool, together with extensive meteorology, remote sensing, and in-situ gas-phase monitoring. The study ran from May 22 – June 22, 2017.
The study was used as an opportunity to compare the widely used and well-established “long DMA” configuration of TSI’s Scanning Mobility Particle Sizer (SMPS™ with model 3081 DMA column paired with model 3785 CPC), against a newly developed commercially available model 3938E77 1-nm SMPS capable of 1-nm sizing. The 1-nm SMPS combines a model 3086 1-nm DMA, model 3777 Nano Enhancer with diethylene glycol working fluid, and model 3772 CPC with butanol working fluid. The 3777 Nano Enhancer uses diethylene glycol to pre-grow particles to ~ 100 nm for CPC detection.
During a majority of the sampling campaign, the 1-nm SMPS was well correlated with the standard SMPS in the overlapping size range of 12 to 32 nm. Preliminary data analysis indicates that within the overlapping range, the mean particle concentrations were 1956 cm^-3 (1-nm SMPS), 1272 cm^-3 (standard SMPS), with a correlation coefficient (r) of 0.93. The correlation coefficient is calculated based on paired hourly data pairs (n=537). Counts were significantly higher on the 1-nm SMPS at sizes less than 20 nm, with increasing divergence between the instruments as size decreased. This is in part due to differences in inlet flows and particle losses between the two instruments.
Several nucleation and growth events were detected with this 1-nm SMPS configuration, with particles detected down to 1.2 nm geometric mean diameter. These events will be placed in context with the 3D and 2D wind fields measured at the site (by SODAR and anemometer, respectively), as well as high time resolution radiation and gas-phase measurements (VOCs, NOx, SO2, nitric acid). The percentage of hours with number concentrations greater than 50 cm^-3 using the 1-nm SMPS in the 1 to 3, and 5 to 10 nm size ranges, was 28% and 73%, respectively.
Ongoing data analysis will further explore the above, as well as any differences in the size distribution caused by drying the standard SMPS while leaving the 1-nm SMPS undried. Finally, periods of very high, and seemingly non-physical, counts detected by the 1 nm SMPS will be explored.