Sachio Ohta

A chemical characterization of atmospheric aerosol in Sapporo

Monthly mean chemical composition of aerosol with diameter less than 8 μm was identified in Sapporo in 1982. The mass of aerosol was made up of nine components: elemental C, organics, SO42−, NO3−, NH4+, Cl−, Na+, soil particles and water. The concentrations of carbonaceous particles (elemental C and organics) was relatively high (12.7–16.0μ m−3) in autumn and winter (October–February) due to emission from domestic heating and comprised 36–41% of total aerosol mass. Higher concentration of soil particles was observed in spring (March–May) (9.7–13.1 μg m−3) and comprised 22–29% of total aerosol mass due to suspension by strong wind. On the other hand, the concentration of excess SO42− (non-sea salt SO42−), which ranged from 2.6–5.2 μg m−3, did not change remarkably with season, and the fraction of excess sulfate increased to 21% in summer (July–August) probably due to photochemical transformation from SO2. Nitrate concentration was far less than that of SO42− throughout the year in Sapporo.

Significance of direct and indirect radiative forcings of aerosols in the East China Sea region

� 8W /m 2 at the top of atmosphere (TOA) and � 10 to � 23 W/m 2 at Earth’s surface of Gosan (33.28N, 127.17E) and Amami-Oshima (28.15N, 129.30E) sites, though there is a large regional difference caused by changes in the aerosol optical thickness and single scattering albedo. The cloud forcing is estimated as � 20 to � 40 W/m 2 , so that the aerosol direct forcing can be comparable to the cloud radiative forcing at surface. However, the estimate of the aerosol direct forcing thus obtained strongly depends on the estimation method of the aerosol properties, especially on the single scattering albedo, generating a method difference about 40%. The radiative forcing of the aerosol indirect effect is roughly estimated from satellite method and SPRINTARS model as � 1t o� 3W /m 2 at both TOA and surface. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 1610 Global Change: Atmosphere (0315, 0325); 9320 Information Related to Geographic Region: Asia;

Activation capability of water soluble organic substances as CCN

Abstract The activation capability of seven dicarboxylic acid compounds, ammonium oxalate, malonic acid, succinic acid, glutaric acid, adipic acid, malic acid and phthalic acid, was determined by laboratory experiments, and predictability by the Kohler theory was discussed. Experimental results showed that ammonium oxalate had the highest capability comparable to that of ammonium sulfate, and malic acid and phthalic acid followed, whereas adipic acid exhibited the lowest capability close to that of an insoluble particle. Malonic acid and glutaric acid were considered to evaporate under normal experimental operations at 8–9% RH but exhibited high and moderate capability, respectively, under supplementary humid operations. The activation capability of succinic acid tended to depend on the laboratory temperatures but was possibly high, comparable to that of malic acid. Particulate drying, associated solute vaporization, morphology and hydrophobicity of particles could be key factors in the theoretical prediction and the interpretation of the experimental results.

Seasonal variation in the chemical composition of atmospheric aerosols and gaseous species in Sapporo, Japan

Abstract Simultaneous samplings of atmospheric aerosols and gaseous precursors (SO2, HNO3,NH3) were conducted during an 18-month period in Sapporo, Japan. The monthly mean mass concentration of particles less than 10 μm in diameter (suspended particulate matter: SPM) and their chemical composition were measured for aerosols collected at two sites located in northern and southwestern regions of the urban area. In the central part of the city, two-week mean concentrations of SO2, HNO3 and NH3 were measured by using tandem filter packs. Seasonal variations of the SPM mass concentrations and composition are discussed along with the results of the gas measurements. In both northern and southwestern regions of the urban area, more than 85% of the mass concentration of SPM is characterized by considering eight major components (elemental carbon, particulate organics, SO42− NO3−, Cl−, NH4, Na+ and soil particles). The concentration of elemental carbon indicates a winter maximum and summer minimum at both sites. Excess SO42− concentrations at the two sites exhibit very similar values throughout the year. An analysis of the concentration of SO2 suggests that the existence of secondarily formed sulfate in the atmosphere may contribute to this feature. Values of NO3− and NH4+ exhibit marked seasonal variations: winter maxima and summer minima. By comparison with the concentration of total. inorganic nitrate ([NO3] in aerosols + [HNO3]) measured in the central part of the city, the variations of NO3− and NH4+ are attributed to the change in the gas-particle phase between HNO3, NH3 and NH4NO3 The measurements of total ammonia ([NH4+] in aerosols + [NH3]) suggest that, in urban area, significant ammonia sources exist other than the ground surface. From the molar equivalence of Na+ and Cl− it was found that the Cl− in SPM aerosols is mostly derived from sea salt; the contribution from NH4Cl is small, even in winter. Furthermore, the measured seasonal variation of Cl− was largely influenced by the chlorine loss from sea salt.

Measurements of particulate carbon in urban and marine air in Japanese areas

Abstract A measurement method for particulate carbon in the atmosphere was developed and applied to carbon measurement in urban and marine air. The amount of particulate carbon collected on quartz fiber filter was determined by sample combustion to produce CO2, followed by catalytic conversion of CO2 to methane, and flame ionization detection. Organic and elemental carbon were separated by oxidation at 300°C. The detection limit of this method was 1 μg carbon 10 cm/t-2 of sample filter. The respective concentrations of atmospheric total and elemental carbons ranged from 1.2 to 3.1 μgC m/t-3 and 0.6 to 1.4 μgC m/t-3 at Hachijo-jima, and 0.8 to 2.5 μgC m/t-3 and 0.4 to 1.3 μgC m−3 at Chichi-jima, respectively in winter. On the Pacific coast of Japan in winter, away from Tokyo Bay, the total and elemental carbon concentrations were horizontally uniform with mean values of about 3 and l μgC m/t-3, respectively in particles with diameter less than 6 μm. In Sapporo they ranged from 4.4 to 14.5 μgC m/t-3 and 2.3 to 8.0 μgC m/t-3, respectively from January to December in 1982. In winter marine air, particulate elemental carbon comprised about 10% of total aerosol mass if sea-salt particles were excluded from the aerosol, and it was 9–23 % of total aerosol mass in Sapporo. The ratio of excess sulfate to elemental carbon could be a good indicator of the formation of sulfate in the atmosphere.

CO2 reduction to CH4 with H2 on photoirradiated TS-1

Abstract CO 2 reduction on reduced titanium silicalite (TS-1) with photoirradiation in the presence of H 2 was investigated in a closed circulation system. CO 2 was reduced to give CH 4 under u.v. irradiation, which TS-1 absorbs. The amount of the carbon species on TS-1 after photoirradiation indicated that all Ti atoms in the framework may act as a photocatalytic site. Infrared spectrum of TS-1 after the reaction showed that CH 2 and CH 3 were left on TS-1.

Optical and chemical properties of urban aerosols in Sendai and Sapporo, Japan

Abstract Simultaneous measurements of size distribution, complex refractive index and chemical components of urban aerosols were intermittently carried out in Sendai and Sapporo, Japan, for the period from February 1986 to June 1987. Applying an inversion-library method to the phase functions measured by a polar nephelometer, size distribution and complex refractive index were retrieved. On the other hand, chemical components were analysed for the aerosol samples on a quartz fiber filter and a Teflon filter collected by two high-volume samplers. Among various components, elemental carbon as well as water content is most effective for the optical properties and its effect is found to be qualitatively different between winter and the other seasons. This difference seems to depend on the contribution of coarse particles.

The causes of elevated concentrations of ozone in Sapporo

In order to investigate the causes of elevated concentrations of O3 in Sapporo which are observed under anticyclonic conditions in spring, we made measurements of O3 concentration at Teine mountain (43°04′N, 141°11′E, 1000m high) in the suburbs of Sapporo simultaneously with measurements of concentrations of HNO3, SO2, SO42−, NO3− and 7Be at ground level in the center of Sapporo in spring 1987. Ozone concentration at Teine mountain showed little diurnal variation. We found remarkably high positive correlation between O3 concentration and temperature at 850 mb, and positive correlation between concentrations of O3 and 7Be. No relationships were found between concentrations of O3 and PAN and between O3 concentration and ƒs (gas-particle distribution factor for S species). Backward trajectory on isentropic surface showed that the air parcel, which originally had existed in the western edge of the upper tropospheric cyclone, descended to the lower troposphere. The results indicate that elevated O3 concentrations in Sapporo in spring were mainly caused by downward transport of O3 from the middle troposphere rather than photochemical formation of O3 in the boundary layer (BL).

Evaluation of absorption properties of atmospheric aerosols at solar wavelengths based on chemical characterization

Abstract The imaginary part of the complex index of refraction of atmospheric aerosols was determined by calculation based on chemical characterization. Atmospheric aerosols in Sapporo were chemically characterized, and were estimated to be mainly composed of elemental C, organics, (NH4)2SO4, NH4NO3, sea salt and soil particles. Using the complex index of refraction of each chemical species, the volume extinction and scattering coefficients of the particles composed of the chemical species were calculated, using Mie scattering theory. The single scattering albedo of the aerosols was obtained as the ratio of the total volume scattering coefficient to the total volume extinction coefficient. The imaginary part of the complex index of refraction of the aerosols was determined by matching the calculated sigle scattering albedo for the aggregate aerosol to that calculated from the sum of the individual aerosol components. The monthly mean imaginary part of the complex index of refraction of aerosols in Sapporo ranged from 0.024 in August to 0.047 in February in 1982. The atmospheric solar heating rate was calculated by solving the equation of radiative transfer in turbid atmospheres. It was estimated that the atmospheric boundary layer in Sapporo was heated at the rate of 2.0–2.5°C day−1 in February as a result of absorption of visible solar radiation by aerosols.

On the rate of homogeneous nucleation in ternary systems

Abstract A kinetic theory of homogeneous nucleation in three component systems is developed by extending the theory of Stauffer (1976) in two component systems. The rotational transformation matrix of coordinates at the saddle point which is expressed by Eulerian angle is determined based on Stauffers speculation that the nucleation current at the saddle point becomes an eigenvector of a matrix involving derivatives of the formation energy and kinetic factors, and by assuming that the formation energy near the saddle point can be approximated due to a quadratic Taylor expansion. A steady-state homogeneous nucleation rate in ternary systems is derived, and if the experimental data on the partial pressure and the surface tension of ternary solution can be obtained, the nucleation rate can be calculated analytically.