The character of single particle sulfate in Baltimore

Derek A. Lake, Michael P. Tolocka, Murray V. Johnston, Anthony S. Wexler

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


A major component of PM 2.5 in urban aerosol in the eastern United States is sulfate. The eastern US is heavily influenced by regional sources (e.g. coal combustion in the Ohio River Valley) and also by local sources. From March to December 2002, the Baltimore aerosol was characterized with the real-time single-particle mass spectrometer RSMS III. RSMS III is capable of simultaneous positive/negative ion detection of size selected particles between 45 and 1250 nm in diameter. The negative ion detection ability allows sulfate to be monitored. Particles were first sorted into two groups based on the negative ion spectra: (1) those with sulfate detected and (2) those with no sulfate detected. The two groups were further sub-divided by ART 2-a analysis of the positive ion spectra to determine which particle compositions are most/least likely to contain detectable sulfate. A separate analysis was also performed on the positive ion spectra to determine the presence/absence of specific metals in the group of particles with and without sulfate. The correlation of positive and negative ion spectra in this manner allows particle types that are strongly associated with sulfate to be distinguished from those which are not. Particle types strongly correlated with sulfate are nitrate, organic carbon/nitrate (OCAN) and vanadium. Particle types weakly associated with sulfate include carbon and potassium/sodium. Many particles contain both sulfate and nitrate, which suggests that they are acid neutralized. While laser ablation mass spectrometry has inherent limitations for particulate sulfate detection, the results presented here suggest that sulfate detection by this method is a reasonable indicator of particle source and atmospheric transformation.

Original languageEnglish (US)
Pages (from-to)5311-5320
Number of pages10
JournalAtmospheric Environment
Issue number31
StatePublished - Oct 2004
Externally publishedYes


  • Ambient aerosol
  • Particle classification
  • Particle size-composition
  • Real-time single-particle mass spectrometry
  • Single particle analysis
  • Sulfate

ASJC Scopus subject areas

  • Atmospheric Science
  • Environmental Science(all)
  • Pollution


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