Two portable aerosol time-of-flight mass spectrometers (ATOFMS) of identical design are described. These instruments are powerful new tools for providing temporal and spatial information on the origin, reactivity, and fate of atmospheric aerosols. Each is capable of analyzing the size and composition of individual particles from a polydisperse aerosol in real-time. Particles are introduced into the instrument through a particle beam interface, sized by measuring the delay time between two scattering lasers, and compositionally analyzed using a dual-polarity laser desorption/ionization time-of-flight mass spectrometer. These are the first dual-ion TOFMS instruments to utilize a dual reflectron design. The instruments measure 72 in. long × 28 in. wide × 60 in. high and weigh ∼500 lb. Pneumatic tires allow them to be transported through standard doorways, elevators, and handicap ramps, granting access to virtually any location. Furthermore, because of rugged construction they will be able to operate during transport by automobile, boat, or aircraft.

The heterogeneous replacement of chloride by nitrate in individual sea-salt particles was monitored continuously over time in the troposphere with the use of aerosol time-of-flight mass spectrometry. Modeling calculations show that the observed chloride displacement process is consistent with a heterogeneous chemical reaction between sea-salt particles and gas-phase nitric acid, leading to sodium nitrate production in the particle phase accompanied by liberation of gaseous HCl from the particles. Such single-particle measurements, combined with a single-particle model, make it possible to monitor and explain heterogeneous gas/particle chemistry as it occurs in the atmosphere.

This article is one of a series of Fourier transform mass spectrometry (FTMS) reviews that has appeared in this journal at ca. 3–4 year intervals. A comprehensive review of the recent theoretical developments, instrumental developments, electrospray ionization (ESI), and MALDI is given. Ion dissociation techniques are also discussed because of their contributions to gaining insight into chemical structure. Special sections have been devoted to discussing the emerging fields of surface analysis, polymer analysis, Buckminsterfullerenes (buckyballs), and hydrogen/deuterium exchange studies. This review, although not all‐inclusive, is intended to be a starting point for those wishing to learn more about the current status of FTMS, and also as a representative cross‐section of the literature for those familiar with the technique. © 1997 John Wiley & Sons, Inc.

Continuous measurements of single particle size and chemical composition in the atmosphere are made using aerosol time-of-flight mass spectrometers (ATOFMS) operated alongside more conventional reference air sampling instruments at a network of three urban air monitoring sites in southern California. Electrical aerosol analyzers and optical particle counters are employed to acquire continuous particle size distribution data, and inertial impactor and bulk filter samples with 4-h resolution are taken for determination of particle size and chemical composition. Filter and impactor samples also are taken upwind of the air basin at Santa Catalina Island in order to characterize background air quality. The airborne particle size and composition distribution as measured by the cascade impactors at inland sites differ from that over the ocean principally due to depletion of sea salt particles accompanied by the addition of fine carbon-containing particles and secondary aerosol nitrate. Data from the ATOFMS systems create a continuous time series of sodium-, ammonium-, nitrate-, and carbon-containing particle counts that provide a high-resolution view of differences in particle composition as a function of location in the air basin. Results show that the characteristic peak in the Los Angeles area aerosol mass distribution in the 0.2−0.3-μm size range observed during the 1987 SCAQS experiments has been reduced, consistent with reductions in diesel soot and elemental carbon emissions since that time.