CHEMICAL-COMPOSITION OF SINGLE AEROSOL-PARTICLES AT IDAHO-HILL - NEGATIVE-ION MEASUREMENTS

The chemical compositions of single aerosol particles larger than 0.3 mu m optical diameter were measured at Idaho Hill using a laser ioniza tion mass spectrometer. The mass spectrometer can analyze either posit ive or negative ions; this paper covers the negative ion results. Sulf ate, nitrate, organics, O-, and OH- were the most common peaks observe d in the negative ion spectra. Other species identified in the negativ e ion spectra include silicon, chlorine, iodine, organic acids, and el emental carbon. Neither external nor internal mixing completely descri bes the particles: most of the particles were in various classes that were distinctly different from each other. All air masses had more tha n one class of particle present. However, most of the particle classes were in themselves mixtures. Sulfate was the most common negative ion in smaller particles whereas nitrate and complicated mixtures were mo re common in particles larger than about 0.7 mu m. However, nearly all types of particles were observed in all size ranges and wind conditio ns. Aerosol chemistry was not well correlated with gas phase chemistry . Certain combinations, such as nitrate and silicon, were frequently o bserved together in single particles. Sulfate and chlorine did not coe xist in the same particles, nor did silicon and elemental carbon. Smal l amounts of organics were present in most particles. Sulfate and nitr ate were usually, but not always, in different particles. The nitrate/ sulfate ratio estimated with the mass spectrometer data correlated wel l with filter measurements.