Masato Fukuda

Time-resolved measurements of water-soluble organic carbon in Tokyo

[1]xa0Semicontinuous measurements of submicron water-soluble organic carbon (WSOC) aerosol were made simultaneously with organic carbon (OC) and elemental carbon (EC) in the Tokyo urban area in winter, summer, and fall 2004. The measurements of WSOC and OC/EC were made every 6 min and 1 hour, respectively, using a particle-into-liquid sampler (PILS) with a total organic carbon (TOC) analyzer and with an EC-OC analyzer using a thermal-optical technique. The PILS and 12-hour integrated filter measurements of WSOC agreed to within 12%. The WSOC mass concentrations and WSOC/OC ratio showed diurnal variations with peaks at 1200–1400 LT in summer and later in the afternoon in winter. On average, the WSOC/OC ratio was 0.20 and 0.35 μg C/μg C for winter and summer/late fall, respectively. The difference in the winter and summer frequency distributions of the WSOC/OC ratio suggests that the sampled air masses in summer and fall were more photochemically processed than those in winter. Secondary organic carbon (SOC) concentrations were estimated using the EC-tracer method. The measured WSOC was highly correlated with the derived SOC (r2 = 0.61–0.79), with WSOC/SOC slopes of 0.67 to 0.75 μg C/μg C for each season. These results suggest that the WSOC and SOC were similar in their chemical characteristics in this study. Water-insoluble organic carbon (WIOC) ( = OC–WSOC) correlated well with EC and CO (r2 = 0.59–0.73). The diurnally averaged WIOC/EC ratios were nearly constant (1.1 ± 0.1 μg C/μg C) throughout the study periods, suggesting that motor vehicle emissions were an important source of WIOC. A dominant portion (about 90% or more) of the POC was water-insoluble, consistent with previous studies of POC.

Temporal variations of elemental carbon in Tokyo

[1]xa0Mass 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 2003–2005. 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 (ΔEC/ΔCO) is therefore a useful parameter in validating EC emission inventories. The EC concentration and ΔEC/ΔCO showed distinct diurnal variation. On weekdays, EC and ΔEC/ΔCO reached maximum values of about 3 μg m−3 and 9 ng m−3/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 ΔEC/ΔCO 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 ΔEC/ΔCO 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.

Seasonal and diurnal variations of submicron organic aerosol in Tokyo observed using the Aerodyne aerosol mass spectrometer

[1]xa0In situ measurements of trace gases and aerosols were conducted at an urban site in Tokyo (35°39′N, 139°40′E). The data obtained in summer (July–August 2003), fall (September–October 2003), and winter (February 2003 and January–February 2004) are used for the present analysis. Size-resolved chemical composition of nonrefractory (vaporized at 600°C under high vacuum) submicron aerosol was measured using an Aerodyne aerosol mass spectrometer (AMS). Organics are found to be the dominant component (40–60% of total nonrefractory aerosol mass) in all periods. Organic aerosol (OA) is classified by correlation with carbon monoxide (CO) and fragments of aliphatic and oxygenated organic compounds in the AMS mass spectra. Combustion-related organic aerosol (combustion OA) is defined as the primary organic aerosol (POA) fraction, as determined by a linear correlation with CO. Excess organic aerosol (excess OA) is defined by subtracting the combustion OA and the background OA from the total OA. The combustion OA and excess OA show good correlation (r2 = 0.65–0.85) with hydrocarbon-like organic aerosol (HOA) and oxygenated organic aerosol (OOA), respectively, which were derived from a custom principal component analysis. In the summer period the estimated excess OA concentrations show distinct diurnal variations and correlate with ozone (O3) during daytime. On average, the combustion OA does not exhibit a distinct diurnal variation for the summer, fall, and winter periods, while the excess OA shows a clear diurnal pattern (daytime peak at ∼1300 LT). At the daytime peak the excess OA is found to be at nearly the same concentration as the combustion OA for all seasons, suggesting that significant formation of secondary organic aerosol (SOA) occurred in daytime throughout the measurement period.

Urban photochemistry in central Tokyo: 1. Observed and modeled OH and HO2 radical concentrations during the winter and summer of 2004

[1]xa0We used laser-induced fluorescence to measure the concentrations of OH and HO2 radicals in central Tokyo during two intensive campaigns (IMPACT IV and IMPACT L) in January–February and July–August 2004. The estimated detection limit for the 10-min data was 1.3 × 105 cm−3 for the nighttime and 5.2 × 105 cm−3 for the daytime. The median values of the daytime peak concentrations of HO2 were 1.1 and 5.7 pptv for the winter and summer periods, respectively, while the values for OH were 1.5 × 106 and 6.3 × 106 cm−3. High HO2 mixing ratios (>50 pptv) were observed on a day in summer when O3 mixing ratios exceeded 100 ppbv. The average nighttime concentrations of HO2 were 0.7 and 2.6 pptv for the winter and summer periods, respectively, while the values for OH were 1.8 × 105 and 3.7 × 105 cm−3. A photochemical box model constrained by ancillary observations was able to reproduce daytime OH concentrations reasonably well for both periods, although daytime HO2 concentrations were underestimated in winter and overestimated in summer. Increasing the wintertime hydrocarbon concentrations in the model led to an increase in daytime HO2 concentrations, thereby showing better agreement with observations; however, the model continued to underestimate HO2 concentrations at high NO mixing ratios. This underestimate was most pronounced in the mornings of both periods and during the daytime in winter. We studied processes that are capable of explaining this discrepancy, including unknown reactions of HNO4 or an unidentified HOx source that is linearly scalable to the NO mixing ratio. The important processes in terms of producing radicals were the olefin + O3 reactions in the nighttime of both periods and during the daytime in winter, the photolysis of carbonyls in the daytime for both periods, and the photolysis of HONO during the daytime in winter (using measured HONO concentrations) and during mornings in summer (using estimated HONO concentrations).

Partitioning of HNO3 and particulate nitrate over Tokyo : Effect of vertical mixing

[1]xa0Ground-based measurements of gas-phase nitric acid (HNO3) and particulate nitrate (NO3−) were performed in Tokyo during 2003–2004. These measurements provide a comprehensive data set for investigating the diurnal and seasonal variations of gas-phase HNO3 and particulate NO3− and the thermodynamic equilibrium of these compounds. HNO3 and NO3− have distinct diurnal and seasonal variations, especially in summer. This study shows that the thermodynamic equilibrium of HNO3 and NO3− and the production rate of total nitrate (TNO3 = HNO3 + NO3−) are the major controlling factors affecting these seasonal and diurnal variations. A thermodynamic equilibrium model (ISORROPIA) is newly coupled with a one-dimensional (1-D) model to take into account the effect of vertical mixing during daytime on the partitioning of HNO3 and NO3− by constraining the TNO3 concentrations to the observations. The 1-D model reproduces the NO3−/TNO3 ratios observed during daytime, whereas the equilibrium model significantly underestimates these ratios. The agreement between the observed and calculated NO3−/TNO3 ratios is improved over the observed temperature range (1°–34°C) and relative humidity (18–95%) by the 1-D model. These results suggest the importance of vertical mixing in determining HNO3-NO3− partitioning in the boundary layer. It is also found that the mass accommodation coefficient for HNO3 needs to be approximately 0.1 to explain the observed HNO3-NO3− partitioning at the surface.

Evolution of submicron organic aerosol in polluted air exported from Tokyo

[1]xa0Ground-based measurements of aerosols and trace gases were conducted at an urban site in Tokyo (Komaba) and a site 50 km to the north (Kisai) during July–August 2004. An Aerodyne aerosol mass spectrometer (AMS) was deployed at each measurement site to investigate the chemical evolution of submicron organic aerosol (OA) in polluted air. The mass concentrations of OA at the Kisai site were systematically higher than those at the Komaba site and were correlated with ozone under southerly conditions. The rate of increase of OA at the Kisai site is investigated using the photochemical age derived from the ratio of alkyl nitrates to their parent hydrocarbons. The OA concentrations in processed air (age of 8–16 h) were 4–5 times larger than those in fresh emissions (age ∼ 0), suggesting that the OA concentrations can be significantly enhanced within ∼0.5 days under conditions of high photochemical activity.

Mismatch negativity and N2b attenuation as an indicator for dysfunction of the preattentive and controlled processing for deviance detection in schizophrenia: a topographic event-related potential study

The present study compares the amplitudes and topographic patterns of mismatch negativity (MMN) and N2b in schizophrenic patients and normal controls. Twenty-one schizophrenic outpatients and 19 normal volunteers participated in the study. Event-related potentials (ERPs) were recorded in a selective attention task. During the task, subjects were required to focus on one ear, counting deviant stimuli, those deviating in duration from a sequence of standard stimuli. MMN was significantly attenuated in the schizophrenics as compared with the normals in the frontocentral regions. In addition to MMN, the N2b amplitude was also reduced, which showed a significant correlation with the MMN amplitude in the schizophrenics. The late negativity elicited by the deviant stimuli in the unattended condition showed different topographical features between the groups. Whereas the normals showed a lateralized distribution with an ear-related asymmetry, similar to that of the N2b, the schizophrenics showed a frontal dominance, coinciding with the sustained negativity reported by Näätänen et al. (1982), which reflects the automatic preparation for detecting possible subsequent stimulus changes. The amplitude of the sustained negativity was significantly correlated with the performance level in the schizophrenics. The results indicated that although both preattentive and controlled processings are impaired, schizophrenic patients, presumably due to the deficient controlled processing, owe much to automatic processing in the deviant stimulus detection process.

Novel polymorphism in the promoter region of the tumor necrosis factor alpha gene : No association with narcolepsy

The striking evidence of almost 100% association of narcolepsy with human leukocyte antigens (HLA) DR2(DR15) antigen is an important clue to elucidate the molecular basis of this sleep disorder. The gene for tumor necrosis factor alpha (TNF alpha) is located in the HLA class II gene cluster. Recent studies have indicated that TNF alpha plays an important role in the regulation of normal human sleep, and regulation of this cytokine may be disturbed in narcolepsy. We searched for a mutation associated with narcolepsy in the promoter region of the TNF alpha gene by single-strand conformation polymorphism analysis. A novel polymorphism, C-850T, was found in narcoleptic patients. Genotype frequency was examined by restriction fragment length polymorphism method. No significant difference of genotype distribution was found between 92 patients with narcolepsy and 91 normal controls. These results do not support our hypothesis that genetic abnormality of TNF alpha production is pathogenetic for narcolepsy.

Formation and transport of oxidized reactive nitrogen, ozone, and secondary organic aerosol in Tokyo

[1]xa0Measurements of the major reactive nitrogen species (NOy)i (NOx, peroxyacyl nitrates, HNO3, and particulate nitrate (NO3−)), total reactive nitrogen (NOy), volatile organic compounds, OH and HO2, and organic aerosol were made near the urban center of Tokyo in different seasons of 2003–2004 to study the processes involving oxidized forms of reactive nitrogen and O3. Generally, NOx constituted the dominant fraction of NOy throughout the seasons. The NOx/NOy and HNO3/NOy ratios were lowest and highest, respectively, in summer, owing to the seasonally high OH concentration. The fraction of NOy that remained in the atmosphere after emission (RNOy) decreased with the decrease in the NOx/NOy ratio in summer and fall. It is likely that the median seasonal-diurnal variations of Ox = O3 + NO2 were controlled by those of the background O3 levels, photochemical O3 formation, and vertical transport. Ox showed large increases during midday under stagnant conditions in mid-August 2004. Their in situ production rates calculated by a box model were too slow to explain the observed increases. The high Ox was likely due to the accumulation of Ox from previous days in the upper part of the boundary layer (BL) followed by transport down to near the surface by mixing after sunrise. Considering the tight correlation between Ox and secondary organic aerosol (SOA), it is likely that SOA also accumulated during the course of sea-land breeze circulation in the BL.

Urban photochemistry in central Tokyo: 2. Rates and regimes of oxidant (O3 + NO2) production

[1]xa0Net photochemical production rates of oxidant (Ox = O3 + NO2), F-D(Ox), were determined in Tokyo during the winter and summer of 2004 using observed and calculated HO2 radical concentrations. In both cases, calculated RO2 (organic peroxy) radical concentrations were used. The rates calculated using the two HO2 data sets are similar. In summer, morning F-D(Ox) values on smog days (those with midday O3 concentrations exceeding 100 ppbv) were higher than those on smog-free days (with typical midday O3 concentrations of 30 ppbv); however, the amount of ozone produced in a single day, as estimated by integrating F-D(Ox) over the daytime, was not significantly different for the two periods. This analysis suggests that the occurrence of smog events in the city center cannot readily be explained by day-to-day variations in the strength of in situ photochemistry. On smog days, the coupling of photochemistry and meteorology appears to be important, as air masses in which oxidants accumulated over successive days arrive at the city center at approximately midday, transported by land-sea breeze circulation. The average maximum daytime F-D(Ox) values in summer, 11 and 13 ppbv h−1 using observed and calculated HO2 levels, respectively, were only 1.5 and 2.2 times higher than those in winter (8 and 6 ppbv h−1). In winter, an underestimation of HO2 levels at high NO concentrations resulted in an underestimation of F-D(Ox) when calculated using modeled HO2. While the model predicted a volatile organic compounds (VOC)-limited regime for Ox production in winter, F-D(Ox) based on observed HO2 did not show features of the VOC-limited regime and only steadily increased with increasing NO mixing ratio, even when it exceeded 20 ppbv. In summer, the dependence of F-D(Ox) on nonmethane hydrocarbons (NMHCs) and NOx concentrations was similar in the two cases, in which observed and calculated HO2 levels were used. A VOC-limited regime, predicted on smog-free days, changed to a NOx-limited regime on smog days. The F-D(Ox) values determined for Tokyo are also compared with values for other cities.