Nitrate and oxidized organic ions in single particle mass spectra during the 1999 Atlanta Supersite Project

Abstract

We measured the chemical components of 0.35–2.5 μm diameter aerosols with a Particle Analysis by Laser Mass Spectrometry (PALMS) instrument during the Atlanta Supersite Project in August 1999. This paper presents the results for nitrate and oxidized organics. More than 20% of the negative ion spectra of single particles contained nitrate ion peaks. Nitrate peaks showed a clear maximum during the morning at the time of high ambient relative humidity. Nitrate peaks also had a small local maximum during the afternoon when the gas‐phase HNO3 concentrations were high. This afternoon maximum was more significant for the particles containing soot/hydrocarbons or aluminosilicate components than for the typical organic/sulfate particles. About 45% of negative spectra contained ions indicative of the oxidized organics. Oxidized organic peaks showed a diurnal variation similar to the nitrate: a morning time maximum during the relative humidity maximum and a small maximum in the afternoon. However, in contrast to the nitrate peaks, the afternoon local maximum of oxidized organic peaks was apparent on the organic/sulfate particles. Both nitrate and oxidized organic peaks had larger ion fractions in particles with higher scattered light intensities.