Showing papers by "Yutaka Kondo published in 2010"

Dependence of Laser-Induced Incandescence on Physical Properties of Black Carbon Aerosols: Measurements and Theoretical Interpretation

Abstract: We used a single-particle soot photometer (SP2) to measure the mass of individual black carbon (BC) particles down to ∼ 0.5 fg by means of laser-induced incandescence with an intra-cavity, continuous-wave laser. The incandescence of nine different types of BC samples was investigated to provide a physical basis for choosing appropriate BC materials for SP2 calibration. We estimated the vaporization temperatures of these BC samples from the spectral dependence of incandescence at the limit of the small size parameter x, for which spectral dependence of emissivity is known a priori. The vaporization temperatures differed by less than 2.2% among the samples. For the x 1, the rate of ...

Amplification of Light Absorption of Black Carbon by Organic Coating

Abstract: Photo-absorption by black carbon (BC) aerosol is believed to be enhanced by the internal mixing of BC with volatile compounds. We investigate this effect quantitatively with laboratory experiments....

Oxidant (O3 + NO2) production processes and formation regimes in Beijing

Abstract: [1] For CareBeijing-2006, two sites were established in urban and suburban regions of Beijing in summer 2006. Observations of O3 and its precursors together with meteorological parameters at both sites are presented. Gross ozone production rate P(O3) and sensitivity to nitric oxides (NOx) and volatile organic compounds (VOCs) were investigated using an observation-based photochemical box model (OBM). P(O3) varied from nearly zero to 120 and 50 ppb h−1 for urban and suburban sites, respectively. These rates were greater than the accumulation rates of the observed oxidant (O3 + NO2) concentrations. The O3 episodes typically appeared under southerly wind conditions with high P(O3), especially at the urban site. Sensitivity studies with and without measured nitrous acid (HONO) as a model constraint suggested that the estimated P(O3) at both sites was strongly enhanced by radical production from HONO photolysis. Both NOx- and VOC-sensitive chemistries existed over time scales from hours to days at the two sites. The variation in O3-sensitive chemistry was relatively well explained by the ratio of the average daytime total VOC reactivity (kTVOC) to NO, with the transition chemistry corresponding to a kTVOC/NO value of 2–4 s−1 ppb−1. Pronounced diurnal variations in the O3 production regime were found. In the morning, conditions were always strongly VOC-limited, while in the afternoon, conditions were variable for different days and different sites. The model-calculated results were tested by measurements of H2O2, HNO3, total OH reactivity, and HOx radicals. The OBM was generally capable of correctly simulating the levels of P(O3), although it might tend to overpredict the VOC-sensitive chemistry.

Formation and Transport of Aerosols in Tokyo in Relation to Their Physical and Chemical Properties: A Review

Abstract: Large amounts of reactive gases and aerosols are emitted from urban areas. Megacities, including the Tokyo Metropolitan Area (TMA), are very large, concentrated sources of these species affecting local, regional, and global ozone (O3) and aerosol levels. Emissions strongly influence air quality and climate on these scales. In 2003-2004, we made intensive measurements of O3 and chemical composition of aerosol particles with diameters less than 1 µm (PM1 aerosol) together with their precursors for the first time in Tokyo, Japan, as a part of the series of Integrated Measurement Program for Aerosol and Oxidant Chemistry in Tokyo (IMPACT) campaigns. Using these data, we investigated the formation and transport processes of O3 and PM1 aerosols through the analysis of their temporal variations near the urban center of Tokyo and regions downwind. Key findings obtained in these studies are reviewed in this paper.

Spatial and temporal variations of aerosols around Beijing in summer 2006: 2. Local and column aerosol optical properties

Abstract: [1] Model calculations were conducted using the Weather Research and Forecasting model coupled with chemistry (WRF-chem) for the region around Beijing, China, in the summer of 2006, when the CAREBeijing-2006 intensive campaign was conducted. In this paper, we interpret aerosol optical properties in terms of aerosol mass concentrations and their chemical compositions by linking model calculations with measurements. The model calculations generally captured the observed variability of various surface and column aerosol optical parameters in and around Beijing. At the surface, the spatial and temporal variations of aerosol absorption and scattering coefficients corresponded well to those of elemental carbon and sulfate mass concentrations, respectively, and were controlled by local-scale (<100 km and <24 hours) and regional-scale (<500 km and <3 days) emissions, respectively. The contribution of secondary aerosols and their water uptake increased with altitude within the planetary boundary layer. This variation led to a considerable increase in column aerosol optical depth and was responsible for the differences in regional and temporal variations between surface and column aerosol optical properties around Beijing. These processes are expected to be common in other megacity regions as well. Model calculations, however, underestimated or overestimated the absolute levels of aerosol optical properties in and around Beijing by up to 60%. Sensitivity studies showed that these discrepancies were mostly due to the uncertainties in aerosol mixing state and aerosol density (affecting mass extinction efficiency) in the model calculations. Good agreement with measurements is achieved when these aerosol properties are accurately predicted or assumed; however, significant bias can result when these properties are inadequately treated, even if total aerosol mass concentrations are reproduced well in the model calculations.

Particle pollution in Beijing: features, source and secondary formation

Abstract: As the capital of China and a major mega city, Beijing has been experiencing great changes in recent years. Particulate pollution is reported to be the major air pollutant in Beijing for about 85% of days in the last 5 years (Beijing Environmental Bulletin, 2004-2008). Meanwhile totally 15 stages control measures for air pollution have been taken since 1998, and enhanced strongly for the 2008 Olympic Games. Although great effort has been made by Beijing’s government to mitigate atmospheric particulate pollution, PM10 levels are still over the target levels and have become the major air pollution problem in Beijing. Moreover, the presence of regional and secondary pollution has been recently recognized. Organic matter constitutes a major fraction of PM2.5 mass, and the difference in OC/EC ratios from other cities indicates a distinct source in Beijing. A two-year measurement of organic species and source apportionment by receptor models showed that coal combustion and cooking emissions are unique in Beijing. Coal combustion and vehicle emissions as well as various dusts are important sources for particle pollution in China. Secondary organic carbon comprises a major fraction of OC, with the highest contribution to total OC in summer (45%) and the lowest in winter (19%). However, because some uncertainties still exist, the contributions and formation mechanisms of secondary compounds will require intense investigation in the future. New particle formation events as a source of secondary aerosol are observed on about 20% of the days each year in Beijing, with the highest frequency in spring and lowest in summer. An optical closure study showed that a Mie model can acceptably reproduce the aerosol optical properties in Beijing. This study also highlights the importance of coating on soot in enhancing the aerosol absorption and scattering coefficients.