Showing papers by "Yutaka Kondo published in 2013"

Bounding the role of black carbon in the climate system: A scientific assessment

Abstract: Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption; influence on liquid, mixed phase, and ice clouds; and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related, namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr−1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models and should be increased by a factor of almost 3. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W m−2 with 90% uncertainty bounds of (+0.08, +1.27) W m−2. Total direct forcing by all black carbon sources, without subtracting the preindustrial background, is estimated as +0.88 (+0.17, +1.48) W m−2. Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 W m−2 with 90% uncertainty bounds of +0.17 to +2.1 W m−2. Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1 W m−2, is the second most important human emission in terms of its climate forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short-lived species that may either cool or warm climate. Climate forcings from co-emitted species are estimated and used in the framework described herein. When the principal effects of short-lived co-emissions, including cooling agents such as sulfur dioxide, are included in net forcing, energy-related sources (fossil fuel and biofuel) have an industrial-era climate forcing of +0.22 (−0.50 to +1.08) W m−2 during the first year after emission. For a few of these sources, such as diesel engines and possibly residential biofuels, warming is strong enough that eliminating all short-lived emissions from these sources would reduce net climate forcing (i.e., produce cooling). When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all short-lived species from black-carbon-rich sources becomes slightly negative (−0.06 W m−2 with 90% uncertainty bounds of −1.45 to +1.29 W m−2). The uncertainties in net climate forcing from black-carbon-rich sources are substantial, largely due to lack of knowledge about cloud interactions with both black carbon and co-emitted organic carbon. In prioritizing potential black-carbon mitigation actions, non-science factors, such as technical feasibility, costs, policy design, and implementation feasibility play important roles. The major sources of black carbon are presently in different stages with regard to the feasibility for near-term mitigation. This assessment, by evaluating the large number and complexity of the associated physical and radiative processes in black-carbon climate forcing, sets a baseline from which to improve future climate forcing estimates.

Development and validation of a black carbon mixing state resolved three-dimensional model: Aging processes and radiative impact

Abstract: [1] A new two-dimensional aerosol bin scheme, which resolves both aerosol size and black carbon (BC) mixing state for BC aging processes (e.g., condensation and coagulation) with 12 size × 10 mixing state bins, has been developed and implemented into the WRF-chem model (MS-resolved WRF-chem). The mixing state of BC simulated by this model is compared with direct measurements over the East Asian region in spring 2009. Model simulations generally reproduce the observed features of the BC mixing state, such as the size-dependent number fractions of BC-containing and BC-free particles and the coating thickness of BC-containing particles. This result shows that the model can simulate realistic BC mixing states in the atmosphere if condensation and coagulation processes are calculated explicitly with the detailed treatment of BC mixing state. Sensitivity simulations show that the condensation process is dominant for the growth of thinly coated BC particles, while the coagulation process is necessary to produce thickly coated BC particles. Off-line optical and radiative calculations assuming an average mixing state for each size bin show that the domain- and period-averaged absorption coefficient and heating rate by aerosols are overestimated by 30–40% in the boundary layer, compared with a benchmark simulation with the detailed treatment of mixing state. The absolute value of aerosol radiative forcing is also overestimated (10%, 3 W m–2) at the surface. However, these overestimations are reduced considerably when all the parameters (including mass and number concentration) are calculated with the simple treatment of mixing state. This is because the overestimation of radiative parameters due to higher absorption efficiency (compared with the benchmark simulation) is largely canceled by the underestimation of BC concentrations due to efficient wet removal processes. The overall errors in radiative forcing can be much smaller because of this cancellation, but for the wrong reasons.

Comparison of Black Carbon Mass Concentrations Observed by Multi-Angle Absorption Photometer (MAAP) and Continuous Soot-Monitoring System (COSMOS) on Fukue Island and in Tokyo, Japan

Abstract: Reducing uncertainties associated with measurements of black carbon (BC) particles is critical for improved quantification of their impacts on climate and health. We compared BC measurements using a continuous soot-monitoring system (COSMOS) and a multi-angle absorption photometer (MAAP) to assess their uncertainties. We found that measurements by COSMOS and MAAP instruments correlate strongly to each other, and their hourly ratio showed minimal temporal variations, but the MAAP values were systematically higher by a factor of 1.56 ± 0.19 (1σ), based on simultaneous observations on Fukue, a remote island in Japan, for about a year. This factor was almost independent of the air mass origins and seasons. Measurements in central Tokyo for about 2 months also yielded a similar relationship, with a systematic difference factor of ∼1.8. It is likely that the systematic differences are caused by differences in the conditions/protocols in the thermal/optical BC determinations used for calibration of each optical ...

Evaluation of a Method to Measure Black Carbon Particles Suspended in Rainwater and Snow Samples

Abstract: We conducted a detailed evaluation of a method for measuring the mass concentrations and size distributions of black carbon (BC) particles in rainwater and snow. The method uses an ultrasonic nebulizer (USN) and a single particle soot photometer (SP2). The USN disperses sample water into micron-size droplets at a constant rate and then dries them to release BC particles into the air. The masses of individual BC particles are measured by the SP2, using the laser-induced incandescence technique. The loss of BC particles during the extraction from liquid water to air depends on their sizes. We determined the size-dependent extraction efficiency using polystyrene latex (PSL) spheres with 12 different diameters between 107 and 1025 nm. The PSL concentrations in water were measured by the light extinction at 532 nm. The extraction efficiency of the USN showed a broad maximum of about 10% in the diameter range 200–500 nm and decreased substantially at larger sizes. The accuracy and reproducibility of the measure...

Vertical transport mechanisms of black carbon over East Asia in spring during the A-FORCE aircraft campaign

Abstract: [1] Mechanisms of vertical transport of black carbon (BC) aerosols and their three-dimensional transport pathways over East Asia in spring were examined through numerical simulations for the Aerosol Radiative Forcing in East Asia (A-FORCE) aircraft campaign in March–April 2009 using a modified version of the Community Multiscale Air Quality (CMAQ) modeling system. The simulations reproduced the spatial distributions of mass concentration of BC and its transport efficiency observed by the A-FORCE campaign reasonably well, including its vertical and latitudinal gradients and dependency on precipitation amount that air parcels experienced during the transport. During the A-FORCE period, two types of pronounced upward BC mass fluxes from the planetary boundary layer (PBL) to the free troposphere were found over northeastern and inland-southern China. Over northeastern China, cyclones with modest precipitation were the primary uplifting mechanism of BC. Over inland-southern China, both cumulus convection and orographic uplifting along the slopes of the Tibetan Plateau played important roles in the upward transport of BC, despite its efficient wet deposition due to a large amount of precipitation supported by an abundant moisture supply by the low-level southerlies. In addition to the midlatitude (35–45°N) eastward outflow within the PBL (21% BC removal by precipitation during transport), the uplifting of BC over northeastern and inland-southern China and the subsequent BC transport by the midlatitude lower tropospheric (50% BC removal) and subtropical (25–35°N) midtropospheric westerlies (67% BC removal), respectively, provided the major transport pathways for BC export from continental East Asia to the Pacific.

Seasonal variations of Asian black carbon outflow to the Pacific: Contribution from anthropogenic sources in China and biomass burning sources in Siberia and Southeast Asia

Abstract: [1] The Community Multiscale Air Quality model with a source and process tagged method (CMAQ/PASCAL) was used to understand source regions and types (anthropogenic (AN) and biomass burning (BB)) of Asian black carbon (BC) outflow to the Pacific during 2008–2010. The model simulations generally reproduced absolute concentrations and temporal (seasonal, monthly, and day-to-day) variations of BC mass concentrations, observed by both surface and aircraft measurements in outflow regions in East Asia. These model simulations show that both the total eastward flux and transport efficiency (fractions transported from sources) of BC are highest during spring (26 kg s−1 and 33% at 150°E) and lowest during summer (8 kg s−1 and 20% at 150°E). These seasonal variations of Asian BC outflow are generally controlled by transport patterns (monsoons, frontal passages, and convection) and emissions from the following three sources: (1) AN emissions from China (China AN), (2) BB emissions from Southeast Asia and South China (SEA BB) during February–April, and (3) BB emissions from Siberia and Kazakhstan (Siberia BB) during April–July. In our simulations, China AN dominates the total eastward BC flux on a 3 year average (61%, 17%, and 6% from China AN, Siberia BB, and SEA BB, respectively, at 150°E). In contrast, SEA and Siberia BB account for 30–50% of the total eastward BC flux (150°E and 175°E) during spring and summer, and they increase the seasonal variability of the Asian BC outflow flux. BC from Siberia BB is also found to be transported to the Pacific more efficiently than BC from other sources. Although the magnitudes of BB emissions are highly uncertain, our results suggest that the control of Siberia BB will be important in terms of the transboundary transport of BC to the Pacific, North America, and the Arctic.

Top-down estimate of China's black carbon emissions using surface observations: Sensitivity to observation representativeness and transport model error

Abstract: [1] This study examines the sensitivity of “top-down” quantification of Chinese black carbon (BC) emissions to the temporal resolution of surface observations and to the transport model error associated with the grid resolution and wet deposition. At two rural sites (Miyun in North China Plain and Chongming in Yangtze River Delta), the model-inferred emission bias based on hourly BC observations can differ by up to 41% from that based on monthly mean observations. This difference relates to the intrinsic inability of the grid-based model in simulating high pollution plumes, which often exert a larger influence on the arithmetic mean of observations at monthly time steps. Adopting the variation of BC to carbon monoxide correlation slope with precipitation as a suitable measure to evaluate the model's wet deposition, we found that wet removal of BC in the model was too weak, due in part to the model's underestimation of large precipitation events. After filtering out the observations during high pollution plumes and large precipitation events for which the transport model error should not be translated into the emission error, the inferred emission bias changed from −11% (without filtering) to −2% (with filtering) at the Miyun site, and from −22% to +1% at the Chongming site. Using surface BC observations from three more rural sites (located in Northeast, Central, and Central South China, respectively) as constraints, our top-down estimate of total BC emissions over China was 1.80 ± 0.65 Tg/yr in 2006, 0.5% lower than the bottom-up inventory of Zhang et al. (2009) but with smaller uncertainty.

Seasonal variations of black carbon observed at the remote mountain site Happo in Japan

Abstract: [1] The emission of black carbon (BC) from East Asia and its long-range transport strongly influence the mass concentration of BC (MBC) over the western Pacific. However, reliable and long-term BC data are still limited in this region, especially at elevated altitudes. In this study, we present accurate measurements of MBC using a continuous soot monitoring system at Happo, a remote mountain site at an altitude of about 1.8 km in Japan, from August 2007 to August 2009. The annual average MBC at Happo was about 0.26 ± 0.18 (1σ) µg m−3. The monthly average MBC values exhibited similar seasonal variations during both years, with minimum values in winter. Around 40% of the air sampled at the site was of free tropospheric (FT) origin, with about 10% originating in North China (NC) origin, respectively. The MBC values for FT (0.24 µg m−3) and NC (0.23 µg m−3) air were representative of the MBC values (0.26 µg m−3) at 1.8 km height in the western Pacific, which are strongly influenced by BC emissions in North China. The MBC values calculated using a regional-scale model reproduced well the MBC observed at Happo. The model predicted that BC transported from northern China alone contributed ~53% to the measured MBC, consistent with trajectory analysis. The comparison of model-calculated and observed MBC values indicates that the minimum values of MBC in winter were caused by the suppressed upward transport of BC over the Asian continent. Biomass burning in Siberia substantially increased MBC in the spring of 2008.

Evaluation of a Heated-Inlet for Calibration of the SP2

Abstract: Black carbon (BC) calibration standards, such as fullerene soot, are routinely used to calibrate single-particle soot photometer (SP2) instruments. Impurities in BC standards create uncertainties in these calibrations, and thus it is desirable to remove non-BC compounds from the aerosol, though removal processes must not significantly alter BC microphysical properties. We present a series of experiments using mobility- and mass-selected fullerene soot particles to assess the performance of a high-temperature denuder system for treating BC prior to SP2 analysis. Particle mass, incandescence, and scattering properties were measured by tandem aerosol particle mass analyzers and an SP2, after thermal treatment at a range of temperatures and residence times (RT). For a longer RT (e.g., ∼6 s at 300°C), monodisperse fullerene soot particles of initial mass 1.4 fg decreased in mass with increasing temperature, by 3% at 300°C to 15% at 600°C. Mass losses were similar for fullerene soot particles of initial mass 10...

Size-resolved measurement of the mixing state of soot in the megacity Beijing, China: Diurnal cycle, aging and parameterization

Abstract: In the summer of 2006, measurements of the mixing state of non-volatile particles were carried out at a suburban site of Beijing in the North China Plain by using a VTDMA. In this study, we perform an in-depth analysis of VTDMA results, focusing on the following topics: (1) comparison of the mixing state of soot measured by a VTDMA and the aerosol hygroscopicity mixing state determined by a CCN (cloud condensation nuclei) counter; (2) diurnal variation and evolution of soot mixing state at different size ranges; (3) calculation of kex→in and the influence of emissions on it; and (4) potential parameterization methods.

Seasonal variations of Asian black carbon outflow to the Pacific: Contribution from anthropogenic sources in China and biomass burning sources in Siberia and Southeast Asia

Abstract: [1] The Community Multiscale Air Quality model with a source and process tagged method (CMAQ/PASCAL) was used to understand source regions and types (anthropogenic (AN) and biomass burning (BB)) of Asian black carbon (BC) outflow to the Pacific during 2008–2010. The model simulations generally reproduced absolute concentrations and temporal (seasonal, monthly, and day-to-day) variations of BC mass concentrations, observed by both surface and aircraft measurements in outflow regions in East Asia. These model simulations show that both the total eastward flux and transport efficiency (fractions transported from sources) of BC are highest during spring (26 kg s−1 and 33% at 150°E) and lowest during summer (8 kg s−1 and 20% at 150°E). These seasonal variations of Asian BC outflow are generally controlled by transport patterns (monsoons, frontal passages, and convection) and emissions from the following three sources: (1) AN emissions from China (China AN), (2) BB emissions from Southeast Asia and South China (SEA BB) during February–April, and (3) BB emissions from Siberia and Kazakhstan (Siberia BB) during April–July. In our simulations, China AN dominates the total eastward BC flux on a 3 year average (61%, 17%, and 6% from China AN, Siberia BB, and SEA BB, respectively, at 150°E). In contrast, SEA and Siberia BB account for 30–50% of the total eastward BC flux (150°E and 175°E) during spring and summer, and they increase the seasonal variability of the Asian BC outflow flux. BC from Siberia BB is also found to be transported to the Pacific more efficiently than BC from other sources. Although the magnitudes of BB emissions are highly uncertain, our results suggest that the control of Siberia BB will be important in terms of the transboundary transport of BC to the Pacific, North America, and the Arctic.

Condensation Particle Counters Combined with a Low-Pressure Impactor for Fast Measurement of Mode-Segregated Aerosol Number Concentration

Abstract: An integrated airborne system comprising two condensation particle counters (CPCs, models 3771 and 3772, TSI Inc.) and a low-pressure impactor (LPI) has been developed (LPI-CPCs) for fast measurement of mode-segregated aerosol number concentration. The CPC 3771 is connected to the LPI to measure aerosol number concentrations below 0.17 μm in aerodynamic diameter, while the CPC 3772 directly measures the total aerosol number concentration. The former approximately corresponds to the Aitken mode fraction of the aerosol number concentration. The key concept is that the cutoff diameter of the LPI (aerodynamic diameter at which the transmission efficiency is 50%) is controlled by simultaneously modifying the pressure and flow rate through the LPI. The instrument was deployed onboard the King Air B200T aircraft during the Aerosol Radiative Forcing in East Asia (A-FORCE) conducted over the western Pacific in the spring of 2009. The results from the aircraft measurements, together with those from laboratory exper...

A new theoretical method for calculating temperature and water vapor saturation ratio in an expansion cloud chamber

Abstract: Received 15 November 2012; revised 17 May 2013; accepted 22 May 2013; published 26 June 2013. [1] The expansion cloud chamber is a widely used apparatus for investigating the dynamics of condensational growth of aerosols and clouds. Theoretical calculations of temperature T and water vapor saturation ratio S are necessary for quantitative interpretations of experimental data obtained from the expansion cloud chamber. In this paper, we revisit the thermodynamics associated with the underlying assumptions for calculating the time-dependent temperature T(t) and saturation ratio S(t) in an expansion chamber as a function of experimentally observable parameters. We introduce an intuitive and robust method, the virtual path (VP) method, by which changes in the thermodynamic state of a moist air parcel containing cloud droplets are schematically represented on a thermodynamic diagram. The validity of the VP method is confirmed by comparisons with the differential equation (DE) method, which is a numerical simulation of real physical processes according to the time evolution equations involving T and S. In contrast to the conventional DE method, the governing equations of the VP method do not involve time t, an irrelevant parameter in the framework of classical thermodynamics. The VP method is advantageous compared to the DE method because the former is applicable to the raw experimental data acquired with a finite time resolution, allowing a robust calculation of the T and S values and the errors that are only caused by the measurement errors of the input data.

Corona-Imaging Colorimetric Method for Accurate Measurement of the Size of Water Droplets in an Expansion Chamber

Abstract: Accurate and time-resolved measurement of the size of water droplets is a prerequisite for the study of the microphysical processes of cloud formation by using an expansion chamber. We developed a droplet sizing method that uses color images of coronae observed under illumination of a white-light beam, also known as the corona-imaging colorimetry (CIC) method. In the CIC method, RGB data from images obtained by a commercial digital camera are converted into standard colorimetric parameters. The droplet size is estimated by optimizing the agreement of the measured colorimetric parameters with those estimated from Mie theory. For polystyrene latex spheres suspended in water, the particles size estimated by the CIC method agrees to within 2% of the predetermined value. We apply this method to the time-resolved measurement of the size of water droplets formed in an expansion chamber. The CIC method is technically simple and enables accurate and instantaneous measurements of the size of droplets with diameters...