Fig. 6.

PALMS negative ion mass spectra of ice-crystal residual particles typical of homogeneous-freezing conditions in two different types of air masses. (Upper) A negative polarity spectrum obtained on November 16. This particle, as well as the background aerosol, had minimal organics, instead being relatively pristine sulfates. Conversely, Lower shows a negative polarity spectrum obtained on November 17 that also coexhibits several organic fragments (as did the background aerosol) with sulfate.