HR: 0830h
AN: A21E-1024    [PDF]
TI: Single Particle Mass Spectroscopy: A Comparative Study Between Houston and NYC
AU: * Imre, D
EM: dan.imre@pnl.gov
AF: pnnl, MSIN K9-34, P.O. 999, richland, wa 99352
AU: Zelenyuk, A
EM: alla.zelenyuk@pnl.gov
AF: pnnl, MSIN K9-34, P.O. 999, richland, wa 99352
AB: We will present results from two field programs where our Single Particle Laser Ablation Time of Flight Mass Spectrometer (SPLAT-MS) was deployed. SPLAT-MS provides size and chemical composition of individual aerosol particles obtained by real-time sampling directly from ambient air. An aerodynamic lens is used to focus between 50 and 90 percent of entrained particles in the 50nm to 3.5micron into an extremely narrow beam. Two-stages of optical detection placed along the well-defined particle beam are used to detect the presence of an incoming particle, measure its velocity from which its aerodynamic diameter can be obtained, and start a clock to generate a trigger to fire the excimer laser. The excimer laser pulse is timed to be coincident with the particles' arrival at the entrance to time of flight MS. When the laser pulse hits the particle it generates ions that are subsequently analyzed in the TOF-MS. At present the instrument is capable of characterizing ~20 particles per second in the 50nm to 3.5micron size range. The combination of the high efficiency inlet with a carefully designed photon counting based optical detection system result in an extremely sensitive instrument that make it possible to characterize particles as small as 50nm with high efficiency. Under most ambient conditions there is a need to dilute the aerosol flow to keep the number of detected particles near 20p/second. A second just as important aspect of SPLAT-MS is SpectraMiner, the data analysis and visualization software that we have developed jointly with SUNYSB. This software makes it extremely easy to cluster the data and then visualize through an interactive interface that is the gateway to data exploration. With a simple click of the mouse one can drill into the data to view individual particle spectra, or alternatively view the data on a coarse scale. The software makes it easy to investigate correlation between classes of aerosols and other observables such as gas phase concentrations, wind direction etc. During 2 weeks of the month of September 2000 SPLAT-MS was sited on the 62nd floor of the Williams Tower located west of the Houston downtown, and west northwest of the ship channel. The high altitude of this site provided a unique opportunity to study particles in the free troposphere and within the boundary layer. A total of 250000 particles were characterized during this period. The smallest particle detected was a 47nm organic nitrate particle. The data show episodic behavior in particle composition that can be correlated with wind direction and gas phase compositions. SPLAT-MS participated in the PMTACS-NY 2001 study during the month of July 2001. We will present data obtained during the period of 8 days when a total of 280000 particles were detected and characterized. Since this was a ground site located relatively close to intense sources much of the observed data is impacted very local sources such as a bus passing by. We will present a comparison between the observations made in Houston and in NY.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0345 Pollution--urban and regional (0305)
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting