Characterization of aerosol particles in the Tokyo metropolitan area using two different particle mass spectrometers

Particle mass spectrometers of two types - a time-of-flight aerosol mass spectrometer (AMS) of Aerodyne Research Inc. and a laser desorption/ionization single particle aerosol mass spectrometer (LISPA-MS) developed at Nagoya University - were deployed to characterize aerosol particles in the Tokyo metropolitan area during the summer of 2008. Based on the ensemble measurements by AMS, equivalent mass concentration of organic aerosol, traced by mass-to-charge ratio (m/z) 44, showed a closer correlation with particulate nitrate and gas-phase odd oxygen, [O₃+NO₂], whereas equivalent mass concentration of organic aerosol, traced by m/z 57, did not. On a particle-by-particle basis, the relative signal peak area of various target species in the LISPA-MS spectra, which was calculated as the ion-signal fraction of the species relative to the total signal peak area summed over all the ion peaks in each spectrum, was used as a measure of the relative amount of the species. A rough qualitative agreement was obtained between the temporal variation observed in the LISPA-MS RCOO^- signal and that in the AMS m/z 44, but not the AMS m/z 57, in which the LISPA-MS RCOO^- signal was defined as the sum of the relative signal peak areas of 17 different negative-ion mass peaks used as markers of oxygenated organics. Analysis of the LISPA-MS spectra also showed that approximately 95% of the oxygen-containing organic particles contained nitrate, which is expected to be responsible in part for the correlation between AMS m/z 44 and AMS nitrate.