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Abstract: Due to enforcing vehicle emission reduction requirements in Japan, particulate matter (PM) concentration, especially elemental carbon (EC) concentration in roadside atmosphere, obviously decreased in the last decade. In spite of the previous vehicle emission reduction, EC concentration was not shown a clear decrease, recently. To achieve the PM2.5 environmental standard, measurements based on emission source contribution are desirable. However, source apportionment of carbonaceous aerosol was ambiguous because chemical components are complicated, and the components change through photochemical reaction. The goal of this study is to determine source apportionment for carbonaceous aerosols. Examination of PM2.5 was performed in south Kanto including Tokyo in the summer of 2008 and the winter of 2009. Emissions from the industrial area around Tokyo Bay and the agricultural northern area showed transportation and accumulation due to the seasonal prevailing wind. The emissions formed a geographical distribution due to photochemical reactions. The characteristics of carbonaceous aerosol were obtained using carbon profile analysis and carbon isotope analysis, including the source information such as fossil fuel emission origin, vegetation origin, and combustion product, photochemical reaction product, etc. Soot-EC was found as a substance with fossil fuel origin which did not contain biomass combustion matter, and since it is stable, there was no observed difference by site and a uniform concentration was observed in winter. It became apparent from the carbon isotope analysis using 14C that the carbon from the biomass origin involved 29% in total carbon in the summer, and 48% in winter even at Kudan of central Tokyo. [Copyright &y& Elsevier]

Abstract: The Japanese Ministry of the Environment established a new PM2.5 air quality standard in September 2009, which has lead to increased public interest in air quality improvement. Concentrations of primary particles such as elemental carbon have decreased during the last decade, but secondary particles have become a major concern. When ground-based observations are carried out, the influence of neighboring emissions must be considered. At the same time, as much as possible, particles must be collected in places that will allow the average behavior of secondary particles to be understood. Making observations using aircraft in city skies is advantageous in that samples taken there are not influenced by local exhaust, such observations can cover a wide range at one time, and they are useful in understanding the spatial character of secondary particles. Using a helicopter for sampling, we measured the spatial variation of particle size distribution (0.5–10 μm) on the coastline and over inland areas in the South Kanto region, including the Tokyo metropolitan area, nine times in three days starting on July 30, 2008. The vertical profile of pollutant concentrations was approximately constant between the altitudes of 300 m and 600 m, but concentrations varied both temporally and spatially. Data gathered in level flights at an altitude of 600 m showed that the particle number concentration increased while the mean particle diameter decreased as we flew north (inland). The particle number concentration and its relationship with the mean particle diameter showed a well-organized distribution. A volumetric change of more than 3-fold was seen in the distribution of particles sampled in the inland area, whereas no clear volumetric change was seen in the distribution of particles sampled along the coast. The particle number concentration, mean particle diameter, and particle volume changed at rates of 0.74 cm−3 km−1, −0.48 nm km−1, and 0.057 μm3 cm−3 km−1, respectively, with increasing distance from the coastline. The incremental volumetric growth rates were seen to relate positively in proportion to the NO2 concentration in particular. [Copyright &y& Elsevier]

Abstract: By the reinforcement of the vehicle emission reduction requirement in Japan, the nitrogen oxides (NOx) concentration in a roadside atmosphere decreased clearly recently. However, the ambient nitrogen dioxide (NO2) concentration does not show a substantial decrease. For the forecast of the improvement of the roadside NO2 by the motor vehicle emission regulation, we have been developing a roadside air quality simulation model. The chemical reactions of nitrogen oxide (NO) oxidation with ozone (O3), photodissociation of NO2, and O3 formation were included in this model. This study was carried out to clarify the NO2 behavior near roadside. Involving a spatial distribution of O3 concentration measurement, temporal and spatial variation of NO and NO2 was measured by the devices of chemiluminescence method which were prepared for each species. Concentration change was measured at the same time in four sites every 1 s to pay attention to a percentage of NO2/NOx which varied from route neighborhood to lee side way. The air flow of each sites was monitored by the ultrasonic 3D anemometer. The effect of NO2 concentration change due to the air stagnation or background ozone concentration was evaluated. From the cycle variation of potential ozone (PO) concentration as a function of the elapsed time of the traffic signal, the direct exhaust NO2 was estimated, and, around Noge intersection of Ring 8, Tokyo, 7.3% was obtained as primary NO2 fraction from vehicles. During an advection from the curbside site (0 m) to the 20 m remote site, more than 40% of NO oxidized and generate NO2 at 10 m height. At 3 m height, 7% of NO2 was generated and O3 was consumed in same quantity at the same time. [Copyright &y& Elsevier]

Continuous monitoring of the concentration of atmospheric particulate matter was carried out for 7 years by both gravimetric method and β-ray attenuation method (BAM) from a building rooftop in the Tokyo metropolitan area. The two methods showed a different tendency in each season: the data observed by BAM were higher than those by the gravimetric method in summer, and this difference was reversed in winter. The volatilization of ammonium salts accounted for only 30% of the difference between the monitoring methods in summer. Thus, we considered the differences in the water content measured by each method. The concentration difference between methods increased when relative humidity exceeded the deliquescence point of ammonium sulfate in summer, and the water content was estimated to be 30%. However, differences in relative humidity did not explain why the data obtained by the gravimetric method exceeded BAM data by 20–30% in winter. We found that the gravimetric measurements generally exceeded BAM measurements in winter if the ambient absolute humidity during particle collection was higher than the absolute humidity during sample weighing. The water content of atmospheric aerosols greatly influences their mass concentrations. Care must be taken when using mass concentration data for purposes such as evaluating health effects. [Copyright &y& Elsevier]

Abstract: Non-methane hydrocarbons (NMHCs) are known to have an important role on air quality due to their high reactivity. NMHC analysis has been performed on 148 ambient air samples collected at five different sites in the Kanto area (Tokyo metropolitan area and surrounding six prefectures) of Japan in summer and winter of 2008, and fifty NMHCs have been determined and quantified. A field measurement campaign has been conducted at one of the busiest intersections in Tokyo metropolitan area in winter of 2008. NMHC emissions are evaluated through comparison of distributions of individual NMHCs emitted from motor vehicles, which are estimated from the measurements, with those determined from the current emissions inventory. The comparison revealed that the measured distributions of acetylene, ethylene and toluene showed a good agreement with those estimated from the emissions inventory (the values estimated from the measurements are a factor of 1.5, 0.56 and 2.3 larger than the emissions inventory in median, respectively), however, propane and isobutane are found to be significantly underestimated in the emissions inventory (the measured values were a factor of 18 and 5.1 larger than the emissions inventory, respectively). The significant underestimate of propane can be explained by that the current emissions inventory does not consider emissions from liquefied propane gas (LPG) fueled vehicles. However, for isobutane, reasons for the underestimate are still unclear. Another field measurement has been conducted in summer of 2008, where the air samples have been collected at three different sites on the ground and by a helicopter as well. Remarkable high concentrations of 1-butene and cis- and trans-2-butenes have been sporadically observed in the samples collected at Urayasu in the coastal area of Tokyo bay. Calculated propylene equivalent (PE) concentrations of butenes revealed that those have a significantly important role in ozone formation when the air plume is affected by emissions from their emission sources. The PE concentrations of butenes varied from 0.1 to 39 ppbC, and accounted for 1.5–75% of total PE concentrations at Urayasu. Most of the continuous air quality monitoring stations does not record concentrations of individual hydrocarbons, therefore, the importance of reactive and low concentration hydrocarbon such as butenes might be overlooked in the current emissions inventory and/or air quality model. In this paper, the reliability of NMHC emissions is evaluated based on the field measurements. Their possible impacts on air quality in the Kanto area are discussed as well, based on the calculated propylene equivalent concentrations. [Copyright &y& Elsevier]