NASA - National Aeronautics and Space Administration

The development of a new high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is reported. The high-resolution capabilities of this instrument allow the direct separation of most ions from inorganic and organic species at the same nominal m/z, the quantification of several types of organic fragments (CxHy, CxHyOz, CxHyNp, CxHyOzNp), and the direct identification of organic nitrogen and organosulfur content. This real-time instrument is field-deployable, and its high time resolution (0.5 Hz has been demonstrated) makes it well-suited for studies in which time resolution is critical, such as aircraft studies. The instrument has two ion optical modes: a single-reflection configuration offers higher sensitivity and lower resolving power (up to ∼2100 at m/z 200), and a two-reflectron configuration yields higher resolving power (up to ∼4300 at m/z 200) with lower sensitivity. The instrument also allows the determination of the size distributions of all ions. One-minute detection limits for submicrometer aerosol are <0.04 µg m-3 for all species in the high-sensitivity mode and <0.4 µg m-3 in the highresolution mode. Examples of ambient aerosol data are presented from the SOAR-1 study in Riverside, CA, in which the spectra of ambient organic species are dominated by CxHy and CxHyOz fragments, and different organic and inorganic fragments at the same nominal m/z show different size distributions. Data are also presented from the MIRAGE C-130 aircraft study near Mexico City, showing high correlation with independent measurements of surrogate aerosol mass concentration.