[1] Mass concentrations of elemental carbon (EC) in fine mode and mixing ratios of carbon monoxide (CO) were measured at the University of Tokyo campus in Tokyo in different seasons in [2003][2004][2005]. Measurements of EC were made using a semicontinuous thermal-optical analyzer. The mass concentrations of nonvolatile aerosol measured by the calibrated scanning mobility particle sizer combined with a heated inlet agreed with the independent EC measurements with a systematic difference of about 4%, demonstrating that the mass concentrations of nonvolatile aerosol well represent those for EC. A majority of the nonvolatile aerosol and therefore EC mass concentration was in volume equivalent diameters between 50 and 200 nm, peaking at around 130 nm. The correlation of EC and CO was generally compact throughout the measurement period because of the similarity in sources. The slope of the EC-CO correlation (DEC/DCO) is therefore a useful parameter in validating EC emission inventories. The EC concentration and DEC/DCO showed distinct diurnal variation. On weekdays, EC and DEC/DCO reached maximum values of about 3 mg m À3 and 9 ng m À3 /parts per billion by volume, respectively, in the early morning (0400-0800 local time), when the traffic density of heavy-duty trucks with diesel engines was highest. In addition, these values were lower by a factor of 2 on Sundays. The heavy truck traffic showed similar diurnal and weekday/weekend variations, indicating that exhaust from diesel engines is an important source of EC. Monthly mean DEC/DCO showed a seasonal variation, reaching broad maximum values in spring-autumn and reaching minimum values in midwinter, following the seasonal variation in temperature, as observed in Maryland, United States (Chen et al., 2001). This temperature dependence is likely due to the temperature dependence of EC emissions from diesel engines on intake air temperature. More stringent regulation of emissions of particles from diesel cars started in the Tokyo Metropolitan Area in October 2003. The DEC/DCO values did not change, however, exceeding the natural variability (10%) after 1 year from the start of the new regulations, when the temperature dependence is taken into account. This indicates that the regulation of particle emissions in the Tokyo Metropolitan Area was not effective in reducing the EC concentrations after 1 year.

[1] Semicontinuous measurements of water-soluble organic carbon (WSOC) and organic carbon (OC) in PM 2.5 were made at Gosan, Korea, in March-April 2005. On average, the WSOC/OC mass ratio for all air masses observed at Gosan was 0.30 ± 0.12. WSOC correlated well with CO (r 2 = 0.54) in Chinese outflow, suggesting that a major part of the observed WSOC and/or their precursors was of combustion origin. The relationship between the increase of WSOC and O 3 suggests that the observed WSOC was mostly secondary product. To interpret the measured organic compounds, thermal analyses of organic standards were made in the laboratory. Thermograms of a single standard of water-soluble organic species showed that carbon that evolved at high temperatures (600°-870°C) was generally associated with water-soluble compounds having high molecular weights (MWs) on the order of hundreds, while carbon that evolved at low temperatures (<300°C) generally had MWs of less than $180 g mol À1 . Positive matrix factorization (PMF) analysis revealed three organic compound groups (low, medium, and highly refractory compounds) based on the OC thermograms. On average, highly and low refractory compound groups accounted for 79% and 21% of the WSOC mass, respectively, at Gosan. Highly refractory compound groups significantly contributed to WSOC regardless of air mass origin. The results of the laboratory experiments imply that a large fraction of these highly refractory compound groups was likely associated with high MW compounds. For water-insoluble organic carbon(=OC-WSOC), medium and low refractory compound groups accounted for 60% and 40%, respectively, consistent with the results of the laboratory experiments.

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