Showing papers by "Yutaka Kondo published in 2008"

Atmospheric hydrogen peroxide and organic hydroperoxides during PRIDE-PRD'06, China: their concentration, formation mechanism and contribution to secondary aerosols

Abstract: . Atmospheric hydrogen peroxide (H2O2) and organic hydroperoxides were measured from 18 to 30 July in 2006 during the PRIDE-PRD'06 campaign at Backgarden, a rural site located 48 km north of Guangzhou, a mega-city in southern China. A ground-based instrument was used as a scrubbing coil collector to sample ambient air, followed by on-site analysis by high-performance liquid chromatography (HPLC) coupled with post-column derivatization and fluorescence detection. The H2O2 mixing ratio over the 13 days ranged from below the detection limit to a maximum of 4.6 ppbv, with a mean (and standard deviation) of (1.26±1.24) ppbv during the daytime (08:00–20:00 LT). Methyl hydroperoxide (MHP), with a maximum of 0.8 ppbv and a mean (and standard deviation) of (0.28±0.10) ppbv during the daytime, was the dominant organic hydroperoxide. Other organic peroxides, including bis-hydroxymethyl hydroperoxide (BHMP), peroxyacetic acid (PAA), hydroxymethyl hydroperoxide (HMHP), 1-hydroxy-ethyl hydroperoxide (1-HEHP) and ethyl hydroperoxide (EHP), were detected occasionally. The concentration of H2O2 exhibited a pronounced diurnal variation on sunny days, with a peak mixing ratio in the afternoon (12:00–18:00 LT), but lacked an explicit diurnal cycle on cloudy days. Sometimes a second peak mixing ratio of H2O2 was observed during the evening, suggesting that H2O2 was produced by the ozonolysis of alkenes. The diurnal variation profile of MHP was, in general, consistent with that of H2O2. The estimation indicated that in the morning the H2O2 detected was formed mostly through local photochemical activity, with the rest probably attributable to vertical transport. It is notable that relatively high levels of H2O2 and MHP were found in polluted air. The unexpectedly high level of HO2 radicals detected in this region can account for the production of hydroperoxides, while the moderate level of NOx suppressed the formation of hydroperoxides. High concentrations of hydroperoxides were detected in samples of rainwater collected in a heavy shower on 25 July when a typhoon passed through, indicating that a considerable mixing ratio of hydroperoxides, particularly MHP, resided above the boundary layer, which might be transported on a regional scale and further influence the redistribution of HOx and ROx radicals. It was found that hydroperoxides, in particular H2O2, play an important role in the formation of secondary sulfate in the aerosol phase, where the heterogeneous reaction might contribute substantially. A negative correlation between hydroperoxides and water-soluble organic compounds (WSOC), a considerable fraction of the secondary organic aerosol (SOA), was observed, possibly providing field evidence for the importance of hydroperoxides in the formation of SOA found in previous laboratory studies. We suggest that hydroperoxides act as an important link between sulfate and organic aerosols, which needs further study and should be considered in current atmospheric models.

Radiative impact of mixing state of black carbon aerosol in Asian outflow

Abstract: [1] The radiative impact of the mixing state of black carbon (BC) aerosol is investigated in Asian outflow. The mixing state and size distribution of BC aerosol were measured with a ground-based single-particle soot photometer at a remote island (Fukue) in Japan in spring 2007. The mass concentration of BC in Asian continental air masses reached 0.5 μg m−3, with a mass median diameter of 200–220 nm. The median value of the shell/core diameter ratio increased to ∼1.6 in Asian continental and maritime air masses with a core diameter of 200 nm, while in free tropospheric and Japanese air masses it was 1.3–1.4. On the basis of theoretical calculations using the size distribution and mixing state of BC aerosol, scattering and absorption properties of PM1 aerosols were calculated under both dry and ambient conditions, considering the hygroscopic growth of aerosols. It was estimated that internal mixing enhanced the BC absorption by a factor of 1.5–1.6 compared to external mixing. The calculated absorption coefficient was 2–3 times higher in Asian continental air masses than in clean air. Coatings reduced the single-scattering albedo (SSA) of PM1 aerosol by 0.01–0.02, which indicates the importance of the mixing state of BC aerosol in evaluating its radiative influence. The SSA was sensitive to changes in air mass type, with a value of ∼0.98 in Asian continental air masses and ∼0.95 in Japanese and free tropospheric air masses under ambient conditions.

Aerosol optical properties in a rural environment near the mega-city guangzhou, china: implications for regional air pollution, radiative forcing and remote sensing

Abstract: The scattering and absorption of solar radiation by atmospheric aerosols is a key element of the Earth's radiative energy balance and climate. The optical properties of aerosol particles are, however, highly variable and not well characterized, especially near newly emerging mega-cities. In this study, aerosol optical properties were measured at a rural site approximately 60 km northwest of the mega-city Guangzhou in southeast China. The measurements were part of the PRIDE-PRD2006 intensive campaign, covering the period of 1–30 July 2006. Scattering and absorption coefficients of dry aerosol particles with diameters up to 10 μm (PM 10 ) were determined with a three-wavelength integrating nephelometer and with a photoacoustic spectrometer, respectively. Averaged over the measurement campaign (arithmetic mean ± standard deviation), the total scattering coefficients were 200±133 Mm −1 (450 nm), 151±103 Mm −1 (550 nm) and 104±72 Mm −1 (700 nm) and the absorption coefficient was 34.3±26.5 Mm −1 (532 nm). The average Angstrom exponent was 1.46±0.21 (450 nm/700 nm) and the average single scattering albedo was 0.82±0.07 (532 nm) with minimum values as low as 0.5. The low single scattering albedo values indicate a high abundance, as well as strong sources, of light absorbing carbon (LAC). The ratio of LAC to CO concentration was highly variable throughout the campaign, indicating a complex mix of different combustion sources. The scattering and absorption coefficients, as well as the Angstrom exponent and single scattering albedo, exhibited pronounced diurnal cycles, which can be attributed to boundary layer mixing effects and enhanced nighttime emissions of LAC (diesel soot from regulated truck traffic). The daytime average mid-visible single scattering albedo of 0.87 appears to be more suitable for climate modeling purposes than the 24-h average of 0.82, as the latter value is strongly influenced by fresh emissions into a shallow nocturnal boundary layer. In spite of high photochemical activity during daytime, we found no evidence for strong local production of secondary aerosol mass. The average mass scattering efficiencies with respect to PM 10 and PM 1 concentrations derived from particle size distribution measurements were 2.8 m 2 g −1 and 4.1 m 2 g −1 , respectively. The Angstrom exponent exhibited a wavelength dependence (curvature) that was related to the ratio of fine and coarse particle mass (PM 1 /PM 10 ) as well as the surface mode diameter of the fine particle fraction. The results demonstrate consistency between in situ measurements and a remote sensing formalism with regard to the fine particle fraction and volume mode diameter, but there are also systematic deviations for the larger mode diameters. Thus we suggest that more data sets from in situ measurements of aerosol optical parameters and particle size distributions should be used to evaluate formalisms applied in aerosol remote sensing. Moreover, we observed a negative correlation between single scattering albedo and backscatter fraction, and we found that it affects the impact that these parameters have on aerosol radiative forcing efficiency and should be considered in model studies of the PRD and similarly polluted mega-city regions.

Cloud condensation nuclei activity at Jeju Island, Korea in spring 2005

Abstract: . We measured the number concentrations of cloud condensation nuclei (CCN) and the size distributions of CCN/CN (CN: condensation nuclei) ratios at supersaturations (SSs) of 0.097, 0.27, 0.58, and 0.97% at Jeju Island, Korea during March-April 2005. We made simultaneous measurements of aerosol inorganic ions, water-soluble organic carbon (WSOC), organic carbon (OC), and elemental carbon (EC) in PM2.5. The CCN/CN ratios increased with increasing particle diameter, and the diameter at CCN/CN=0.5 was defined as D50. D50 represents the activation dry diameter of atmospheric particles. The average D50 at SS=0.097% and 0.97% was 136±17 nm and 31±3 nm, respectively. The temporal variation of D50 at SS=0.097% was correlated with the mass fraction of water-soluble components (inorganic ions + WSOC), indicating that the temporal variation of CCN activity was mainly controlled by changes in the water-soluble components fraction. The critical dry diameter (Dcrit), which is the threshold dry diameter for CCN activation, was calculated from the observed aerosol chemical compositions by Kohler theory for comparison with D50. The D50 at SS=0.097% was correlated (r2=0.48) with calculated Dcrit, although Dcrit was larger than D50 by 20–29% on average. The systematic difference between D50 and Dcrit could be caused by the size dependence of the aerosol chemical compositions or surface tension lowering caused by the mixing of water-soluble organic compounds. This difference corresponds to a 27±14% uncertainty in the CCN number concentration estimated from the observed particle number size distribution.

Performance of a newly designed continuous soot monitoring system (COSMOS).

Abstract: We designed a continuous soot monitoring system (COSMOS) for fully automated, high-sensitivity, continuous measurement of light absorption by black carbon (BC) aerosols. The instrument monitors changes in transmittance across an automatically advancing quartz fiber filter tape using an LED at a 565 nm wavelength. To achieve measurements with high sensitivity and a lower detectable light absorption coefficient, COSMOS uses a double-convex lens and optical bundle pipes to maintain high light intensity and signal data are obtained at 1000 Hz. In addition, sampling flow rate and optical unit temperature are actively controlled. The inlet line for COSMOS is heated to 400 °C to effectively volatilize non-refractory aerosol components that are internally mixed with BC. In its current form, COSMOS provides BC light absorption measurements with a detection limit of 0.45 Mm−1 (0.045 µg m−3 for soot) for 10 min. The unit-to-unit variability is estimated to be within ±1%, demonstrating its high reproducibility. The absorption coefficients determined by COSMOS agreed with those by a particle soot absorption photometer (PSAP) to within 1% (r2 = 0.97). The precision (±0.60 Mm−1) for 10 min integrated data was better than that of PSAP and an aethalometer under our operating conditions. These results showed that COSMOS achieved both an improved detection limit and higher precision for the filter-based light absorption measurements of BC compared to the existing methods.

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

Abstract: [1] Net 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.

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

Abstract: [1] Measurements 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.

Dependence of size-resolved CCN spectra on the mixing state of nonvolatile cores observed in Tokyo

Abstract: [1] Size-resolved cloud condensation nuclei (CCN) spectra and volatility tandem differential mobility analyzer (VTDMA) measurements were made simultaneously in Tokyo in wintertime 2007 to characterize CCN activity near the urban center. Ambient particles with mobility diameters of 30–200 nm were investigated at supersaturations (SSs) of 0.32, 0.60, and 0.88%. The size distributions of the nonvolatile cores of size-selected particles measured by the VTDMA were bimodal; one mode showed relatively small changes ( 10% in peak diameter). The former mode is referred to as less volatile (LV), and the latter mode is called more volatile (MV). The main component of nonvolatile cores in Tokyo is known to be black carbon (BC). Therefore, it is likely that LV particles correspond to soot particles. The size-resolved CCN spectra were broader than those of (NH4)2SO4, indicating that the observed particles were not uniformly mixed. In addition, CCN/CN (CN: condensation nuclei) ratios were smaller than unity after the stepwise increase. A CCN-LV correlation analysis shows that for small ( 100 nm), the CCN-inactive fractions were close to the LV particle fractions, suggesting that CCN-inactive particles were composed of fresh soot.

Effects of urban pollution on UV spectral irradiances

Abstract: Spectral measurements of UV irradiances at Tokyo are compared with corresponding measurements at a pristine site (Lauder New Zealand) to identify the causes of the reductions in urban UV irradiances, and to quantify their effects. Tropospheric extinctions in Tokyo were found to be up to ~40% greater than at Lauder. Most of these differences can be explained by differences in cloud and aerosols, but ozone differences are also important in the summer. Examining spectral signatures of tropospheric transmission of both sites shows that reductions due to mean NO 2 and SO 2 amounts are generally small. However, at times the amount of NO 2 can be 10 times higher than the mean amount, and on these days it can decrease the UVA irradiance up to 40%. If SO 2 shows comparable day to day variability, it would contribute to significant reductions in UVB irradiances. The results indicate that at Tokyo, interactions between the larger burden of tropospheric ozone and aerosols also have a significant effect. These results have important implications for our ability to accurately retrieve surface UV irradiances at polluted sites from satellites that use backscattered UV. Supplementary data characterising these boundary layer effects are probably needed.

Photochemical evolution of submicron aerosol chemical composition in the Tokyo megacity region in summer

Abstract: [1] We investigate the chemical transformation of submicron aerosol in the Tokyo megacity region in summer. An Aerodyne quadrupole aerosol mass spectrometer (AMS) was deployed both at an urban site in Tokyo (35°39′N, 139°40′E) and a suburban site (downwind site) in Saitama (36°05′N, 139°33′E) in the summer of 2004. The temporal evolution of size-resolved chemical compositions of submicron (PM1) aerosols during photochemical smog episodes are investigated using the photochemical age derived from the combination of alkyl nitrate-to-hydrocarbon ratio and NOz/NOy ratio (where NOz is defined as the total reactive nitrogen oxides (NOy) excluding nitrogen oxides (NOx)). The photochemical age observed at the downwind site was about 12 h in most aged air. Organic aerosols (OA) and sulfate (SO42−) were major constituents of PM1 aerosols (40–50% and 20–30%, respectively) at both sites during the observation period and their fractions showed no large variation with the NOz/NOy ratio. Mass ratios of OA and SO42− to black carbon (BC) largely increased with the NOz/NOy ratio (by factors of ∼3 and ∼2, respectively), indicating the significance of secondary formation of these compounds in controlling PM1 mass concentrations. We also investigate the photochemical evolution of OA mass spectra observed by the AMS. The mass-to-charge ratio (m/z) peaks of organic compounds relative to BC mass generally showed an increase with the NOz/NOy ratio. These increasing trends vary significantly for different m/z peaks, suggesting the complexity of the temporal evolution of organic functional groups. The m/z 44 and 45 peaks, which are good markers of carboxylic groups in organic particles, showed larger increases than any other m/z peaks, suggesting an efficient formation of carboxylic functional groups on a timescale of hours during the measurement period.

Significant alteration in the hygroscopic properties of urban aerosol particles by the secondary formation of organics

Abstract: [1] The temporal variation in the hygroscopicity of urban aerosol particles was investigated in Tokyo based on the hygroscopic growth factor (g) measurement in the summer of 2004. For 100 nm particles, sporadic appearance of intermediately hygroscopic (1.11 ≤ g < 1.29) particles was observed when the oxygenated organic mass increased (r = 0.76), suggesting that the formation of secondary organics governs the hygroscopicity of these particles. During a photochemically active period in the daytime, the mode hygroscopicity of 100 nm particles above g = 1.11 rapidly decreased in a few hours. This is explained by the condensation of secondary organics on pre-existing particles that are highly hygroscopic (g ≥ 1.29) and are transported from outside the Tokyo metropolitan area. The observed rapid change in particle hygroscopicity suggests that the condensation of secondary organics increase the dry particle diameter at rates of 8–17 nm h−1.

Aerosol optical properties in a rural environment near the mega-city Guangzhou, China: implications for regional air pollution and radiative forcing

Abstract: The scattering and absorption of solar radiation by atmospheric aerosols is a key element of the Earth's radiative energy balance and climate. The optical properties of aerosol particles are, however, highly variable and not well characterized, especially near newly emerging mega-cities. In this study, aerosol optical properties were measured at a regional background site approximately 60 km northwest of the mega-city Guangzhou in southeast China. The measurements were part of the "Program of Regional Integrated Experiments of Air Quality over the Pearl River Delta" intensive campaign (PRIDE-PRD2006), covering the period of 1?30 July 2006. Scattering and absorption coefficients of dry aerosol particles with diameters up to 10 ?m (PM10) were determined with a three-wavelength integrating nephelometer and with a photoacoustic spectrometer, respectively. Averaged over the measurement campaign (arithmetic mean ±standard deviation), the total scattering coefficients were 200±133 Mm?1 (450 nm), 151±103 Mm?1 (550 nm) and 104±72 Mm?1 (700 nm) and the absorption coefficient was 34.3±26.5 Mm?1 (532 nm). The average Angstrom exponent was 1.46±0.21 (450 nm/700 nm) and the average single scattering albedo was 0.82±0.07 (532 nm) with minimum values as low as 0.5. The low single scattering albedo values indicate a high abundance of, as well as strong sources of light absorbing carbon (LAC). The ratio of LAC to CO concentration was highly variable throughout the campaign, indicating a complex mix of different combustion sources. The scattering and absorption coefficients, as well as the Angstrom exponent and single scattering albedo, exhibited pronounced diurnal cycles, which can be attributed to boundary layer mixing effects and enhanced nighttime emissions of LAC (diesel soot from regulated truck traffic). The daytime average single scattering albedo of 0.87 appears to be more suitable for climate modeling purposes than the 24-h average of 0.82, as the latter value is strongly influenced by fresh emissions into a shallow nocturnal boundary layer. In spite of high photochemical activity during daytime, we found no evidence for strong local production of secondary aerosol mass. The relatively low average mass scattering efficiency with respect to PM10 (2.84±0.037 m2 g?1, ?=550 nm) indicates a high proportion of mass in the coarse particle fraction (diameter >1 ?m). During high pollution episodes, however, the Angstrom exponent exhibited a dependence on wavelength, which indicates an enhancement of the fine particle fraction during these periods. A negative correlation between single scattering albedo and backscatter fraction was observed and found to affect the impact that these parameters have on aerosol radiative forcing efficiency.

Mechanisms that influence the formation of high‐ozone regions in the boundary layer downwind of the Asian continent in winter and spring

Abstract: [1] The seasonal variation of ozone (O3) in the boundary layer (BL) over the western Pacific is investigated using a chemistry-transport model. The model results for January and April–May 2002 were evaluated by comparison with PEACE aircraft observations. In January, strong northwesterlies efficiently transported NOx from the continent, leading to an O3 increase of approximately 5–10 ppbv over a distance of about 3000 km. In April, southwesterlies dominated due to anticyclone development over the western Pacific. Along this flow, O3 continued to be produced by NOx emitted from East Asia. This resulted in the formation of a high-O3 (> 50 ppbv) region extending along the coastal areas of East Asia. This seasonal change in O3 was driven in part by a change in the net O3 production rate due to increases in solar UV and H2O. Its exact response depended on the NOx values in the BL. The net O3 production rate increased between winter and spring over the Asian continent and decreased over the remote western Pacific. Model simulations show that about 25% of the total O3 (of 10–20 ppbv) increase over the coastal region of Northeast Asia was due to local production from NOx emissions from China, and the rest was due to changes in background levels as well as emissions from Korea, Japan, and east Siberia. Uplift of BL air over Asia, horizontal transport in the free troposphere, and subsidence were the principal mechanisms of transporting Asian O3 to the central and eastern North Pacific.

Calibration Plan of GOSAT

Abstract: M,**2. +. ,/¬9 ,**2. ,. ,0[Z¬+3 * ­[®ˆ ̄°±\\u2 2-*/ 2/*/ 3] ́zŒμ¶^· , + + * _ ̧`Ÿab1Ÿ ̄° SR 2+/23*. _ ̧c †o»d . 0 + * Japan Aerospace Exploration Agency, , + + Sengen, Tsukuba, Ibaraki -*/ 2/*/, Japan * Research Center for Advanced Science and Technology, The University of Tokyo, . 0 + Komaba, Meguro-ku, Tokyo +/23*., Japan ,**2 RSSJ Journal of The Remote Sensing Society of Japan Vol. ,2 No. , (,**2) pp. +32 ,*-

Aerosol collection system and apparatus and method for analyzing polynuclear aromatic hydrocarbon using the same

Abstract: PROBLEM TO BE SOLVED: To provide an improved aerosol collection system and provide an apparatus and a method capable of measuring PAHs in the atmosphere with high temporal resolution. SOLUTION: A plurality of fine holes are formed in the surface of a collecting plate of the aerosol collection system. Aerosol particles on the collecting plate of the aerosol collection system are rinsed off by a solvent and recovered to a container. Ultrasonic waves are applied to the solution recovered to the container to extract a PAHs solution from the inside of the aerosol. Water is added to the extracted PAHs solution having a small polarity to increase its polarity. The PAHs solution is concentrated by a concentration column. The concentrated PAHs solution is analyzed by a high-performance liquid chromatograph attached with a fluorescence detector or a mass detector in the apparatus and the method for analyzing polynuclear aromatic hydrocarbon. COPYRIGHT: (C)2008,JPO&INPIT