A study on formation process of anthropogenic organic aerosol using a highly advanced mass spectrometer

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1. Improvement of the accuracy of the Aerosol Mass Spectrometer (AMS)The particle collection efficiency (CE) of the AMS depends on relative humidity (RH) in sample air. The temperature of the AMS inlet manifold was maintained at > 10℃ above the ambient dew point to dry particles in the sample air (RH in the inlet < 53%). Assuming CE = 0.5 for the AMS, the mass concentrations of inorganic species (nitrate, sulfate, chloride, and ammonium) measured by the AMS agree with those measured by an Ion Chromatography analyzer (PILS-IC) to within 〜20%.2. Analysis of the mass spectra of selected organic compoundsWe have evaluated the contribution of selected low molecular weight dicarboxylic acids (diacids) to the m/z 44 signal of the AMS mass spectrum. We used ambient measurement data obtained in Tokyo and laboratory experiment data obtained using authentic standards of the selected organic acids. We have reported for the first time that the selected organic acids could account for 14% of the observed m/z 44 signal on average during the measurement period.3. Investigation of the seasonal and diurnal variations of anthropogenic organic aerosol in TokyoIn situ measurements of trace gases and aerosols were conducted at an urban site in Tokyo. Organic aerosol (OA) is classified into primary organic aerosol (POA) and secondary organic aerosol (SOA) using correlation with carbon monoxide (CO). We have found that POA does not exhibit a distinct diurnal variation for the summer, fall, and winter periods, while SOA shows a clear diurnal pattern. We have also found that the OA concentrations can be significantly enhanced within 〜0.5 days under conditions of high photochemical activity.