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A COMPARISON OF PARTICLE MASS SPECTROMETERS DURING THE 1999 ATLANTA SUPERSITES EXPERIMENT
Citation:
Middlebrook, A. M., D. M. Murphy, S. H. Lee, D. S. Thomson, K. A. Prather, R. J. Wenzel, D. Y. Liu, D. J. Phares, K. P. Rhoads, A. S. Wexler, M. V. Johnston, J. L. Jiminez, J. T. Jayne, D. R. Worsnop, I. Yourshaw, J. H. Seinfeld, R. C. Flagan, S. V. Hering, R. J. Weber, P. Jongejan, J. Slanina, AND P. K. Dasgupta. A COMPARISON OF PARTICLE MASS SPECTROMETERS DURING THE 1999 ATLANTA SUPERSITES EXPERIMENT. JOURNAL OF GEOPHYSICAL RESEARCH: ATMOSPHERES 108(D7):SOS 12-1 - 12-13, (2003).
Impact/Purpose:
The PM Supersites Program is an ambient monitoring program intended to address the scientific uncertainties associated with fine particulate matter. The main objectives of the Supersites Program are as follows: 1) characterize particulate matter in a way that contributes to the understanding of source-receptor relationships and supports development of State Implementation Plans (SIPs), 2) develop and test advanced measurement methods for potential use in national monitoring networks, and 3) support health and exposure studies by providing detailed chemical and physical data at one or more central monitoring sites.
The specific objectives of this task are to provide scientific review and coordination of the technical aspects of the Supersites Program. This includes coordination among all Supersites projects and other projects which support Supersites objectives, overseeing of the data management, and coordinating the communication of data analysis and modeling results to the scientific community and other stakeholders. Products include a number of peer-reviewed journal articles (approaching 200 or more), final reports from each project, a relational database than includes not only Supersites data, but most aerometric data collected in the continental US and SE Canada during the period July 2001 to August 2002, and a policy relevant findings synthesis entitled Key and Policy Relevant Findings from the Supersites Program and Related Studies. Also supporting the synthesis is a major international conference where results will be presented from air quality methods, measurements, modeling, and data analysis studies with similar objectives to the Supersites program and during the time period of the Supersites Program, i.e., the last 5-7 years.
Description:
During the Atlanta SuperSite Experiment, four particle mass spectrometers were operated together for the first time: NOAA's PALMS (Particle Analysis by Laser Mass Spectrometry), U. C. Riverside's ATOFMS (Aerosol Time-of-Flight Mass Spectrometry), U. Delaware's RSMS-II (Rapid Single-Particle Mass Spectrometer II), and Aerodyne's AMS (Aerosol Mass Spectrometer). Although these mass spectrometers are generally classified as similar instruments, they clearly have different characteristics due to their unique designs. One primary difference is related to the volatilization/ionization method: PALMS, ATOFMS, and RSMS-II utilize laser desorption/ionization whereas particles in the AMS instrument are volatilized by impaction onto a heated surface with the resulting components ionized by electron impact. Thus, mass spectral data from the AMS are representative of the ensemble of particles sampled and those from the laser-based instruments are representative of individual particles. A main difference among the laser-based mass spectrometers is that the RSMS-II instrument can obtain size-resolved single particle composition information for particles with aerodynamic diameters as small as 15 nm. The minimum sizes analyzed by ATOFMS and PALMS are about 0.2 and 0.35 um, respectively, in aerodynamic diameter. Furthermore, PALMS, ATOFMS, and RSMS-II use different laser ionization conditions. Despite these differences, the laser-based instruments found similar individual particle classifications and their relative fractions among comparable sized particles from Atlanta were broadly consistent. Finally, the AMS measurements of the nitrate/sulfate mole ratio were highly correlated with the quantitative semi-continuous measurements (r 2 = 0.93). In contrast, the PALMS nitrate/sulfate ion ratios were only moderately correlated (r 2 ~ 0.7).
This work was funded in part by the U.S. EPA, NARSTO (Southern Oxidants Study), and Georgia Institute of Technology (SCISSAP).