10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Application of New Butanol-based CPCs to City Air Monitoring and Comparative Instrument Characterization
Andrea Tiwari, Jacob Scheckman, Aaron Avenido, Juergen Spielvogel, AXEL ZERRATH, TSI Incorporated
Abstract Number: 703 Working Group: Instrumentation
Abstract Introduction The new Condensation Particle Counters (TSI model series 375x) have been applied to suburban air quality measurements in winter 2017/18 for further characterization and comparison to other established particle technologies.
Sampling was conducted through a rooftop environmental sampling system with PM10 sampling inlet and a multiple port flow splitter. Environmental data is available from an on-site weather station feeding data into a publicly accessible weather network.
The station is located in a mixed residential and light-industrial area and is close to freight railroad tracks, a railroad junction and an interstate highway, all located within one mile of the sampling location.
The collected data was reviewed with two goals in mind:
1) Observation of ambient air quality using a suite of instruments including the standard submicron sizer (SMPS), two supermicron sizers (APS, OPS) and real-time quartz-crystal microbalance MOUDI impactor (QCM-MOUDI). Particle size, number concentrations, mass concentrations, and mass distributions were all assessed.
2) Inter-comparison of particle counters; the set of three counters included two working fluids (water and butanol) as well as two cutpoints (2.5 and 7 nm).
Results Ambient air observations: - Particle number concentrations: Particle concentrations range from less than 5,000 #/cm³ to up to more than 100,000 #/cm³, depending on wind direction and time of the day, and the activities of local particle sources. This concentration range is typical for city air, and can now be measured accurately using CPC Model 3750, which has an upper concentration limit of 100,000 #/cm³, 10-fold higher than its predecessor. In addition to the upper concentration limit, the cutpoint size of the 3750 CPC – 7 nm – is also appropriate for conducting ambient sampling. Ambient sampling in Europe is governed by the CEN standard (CEN/TS 16796), which specifies that CPCs should have 50% counting efficiency at 7 nm. This cutpoint size is also relevant to ambient sampling in the US, where near-road monitoring frequently uses a 7 nm cutpoint CPC.
- Particle size distributions: The size distribution data recorded with an SMPS scanning from 11 to 478 nm, shows that the majority of particles is <100 nm (ultrafine particle fraction), with occasional events showing up to 200 nm sized particles. Since SMPS data provides insight into changes in particle size with time, it can be a useful supplement to CPC data in that it can suggest changes in particle sources.
Inter-comparison of several particle counters: - Sampling under stable conditions (average temperatures around -6 °C, low wind speed and wind direction mostly from NW) resulted in agreement between two different CPC models to better than 1%. The two models in question had different cutpoints – model 3750 at 7 nm and 3752 at 4 nm – which indicates that the vast majority of ambient particles were larger than 7 nm. The wind direction points to the aerosol being dominated by traffic, with influence from the nearby highway.
- Sampling under transient conditions (characterized by a wind direction change from west to southeast) resulted in agreement between two CPCs of the same cutpoint specification to within 1% with low scatter (r² of 0.94). These two Ultrafine CPCs measured approx. 9% higher number concentrations than the Standard CPC (model 3750 with 7 nm), suggesting that some particles in the ambient air were < 7 nm.
The observations described above support the laboratory instrument characterization results; data from both settings will be presented.