ALBERT

Description: Three-dimensional structures of Asian dust transport in the planetary boundary layer (PBL) and free atmosphere occurring successively during the end of May 2007 were clarified using results of space-borne backscatter lidar, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and results simulated using a data-assimilated version of a dust transport model (RC4) based on a ground-based NIES lidar network. Assimilated results mitigated overestimation of dust concentration by reducing 17.4% of dust emissions and improved the root mean square difference (RMSD) of dust AOT between the model and NIES lidar by 31.2–66.9%. The dust layer depths, vertical and horizontal structure simulated by RC4 agreed with CALIOP from the dust source region to a long-range downwind region for which 3-D distribution of dust clouds had not been clarified previously. Based on CALIOP and RC4, two significant transport mechanisms of Asian dust in the PBL and free atmosphere were clarified: a low level dust outbreak within the dry slot region of a well developed low-pressure system, and formation of an elevated dust layer within the warm sector of a low-pressure system. Finally, the aging of pure dust particles was investigated using the particle depolarization ratio (PDR) at 532 nm and the color ratio (CR) at 1064 nm and 532 nm for the low-altitude dust transport case. Aerosols with high PDR were observed uniformly over the dust source region. As the dust cloud was transported to the eastern downwind regions, aerosols with low PDR and high CR were found in the layer of less than 1 km height, suggesting changes from the external to internal mixing state of spherical aerosols and dust in the surface layer.

Description: Simultaneous ground-based measurements of ozone (O3) and carbon monoxide (CO) were conducted in March 2005 as part of the East Asian Regional Experiment (EAREX) 2005 under the umbrella of the Atmospheric Brown Clouds (ABC) project. Multiple air quality monitoring networks were integrated by performing intercomparison of individual calibration standards and measurement techniques to ensure comparability of ambient measurements, along with providing consistently high time-resolution measurements of O3 and CO at the surface sites in East Asia. Ambient data collected from eight surface stations were compared with simulation results obtained by a regional chemical transport model to infer recent changes in CO emissions from East Asia. Our inverse estimates of the CO emissions from China up to 2005 suggested an increase of 16% since 2001, in good agreement with the recent MOPITT satellite observations and the bottom-up estimates up to 2006. The O3 enhancement relative to CO in continental pollution plumes traversed in the boundary layer were examined as a function of transport time from the Asian continent to the western Pacific Ocean. Comparison of the observed δO3/Δ CO ratios and their modeled spatial distributions suggests an increase in the Δ O3/Δ CO ratio due likely to en-route photochemical O3 formation during eastward transport, confirming that East Asia is an important O3 source region during spring.

Description: Detailed 3-D structures of Trans-Pacific Asian dust transport occurring during 5–15 May 2007 were investigated using the NASA/CALIOP vertical-resolved measurements and a three-dimensional aerosol model (SPRINTARS). Both CALIOP and SPRINTARS dust extinctions showed a good agreement along the way of the transport from the dust source regions across North Pacific into North America. A vertically two-layered dust distribution was observed over the northeastern Pacific and North America. The lower dust layer originated from a dust storm generated in the Gobi Desert on 5 May. It was transported at an altitude of around 4 km MSL and has mixed with Asian anthropogenic air pollutants during the course of transport. The upper dust layer mainly originated from a dust storm that occurred in the Taklimakan Desert 2–3 days after the Gobi dust storm generation. The upper dust cloud was transported in higher altitudes above the major clouds layer during the Trans-Pacific transport. It therefore has remained unmixed with the Asian air pollutants and almost unaffected by wet removal. The decay of its concentration level was small (only one-half after its long-distance transport crossing the Pacific). Our dust budget analysis revealed that the Asian dust flux passing through the longitude plane of 140° E was 2.1 Tg, and one third of that arrived North America. The cases analyzed in this study revealed that, while the Gobi Desert is an important source that can contribute to the long-range dust transport, the Taklimakan Desert appears to be another important source that can contribute to the dust transport occurring particularly at high altitudes.

Description: Detailed 3-D structures of Trans-Pacific Asian dust transport occurring during 5–15 May 2007 were investigated using the NASA/CALIOP vertical-resolved measurements and a three-dimensional aerosol model (SPRINTARS). Both CALIOP and SPRINTARS dust extinctions showed a good agreement along the way of the transport from the dust source regions across North Pacific into North America. A vertically two-layered dust distribution was observed over the northeastern Pacific and North America. The lower dust layer originated from a dust storm generated in the Gobi Desert on 5 May. It was transported at an altitude of around 4 km MSL and has mixed with Asian anthropogenic air pollutants during the course of transport. The upper dust layer mainly originated from a dust storm that occurred in the Taklimakan Desert 2–3 days after the Gobi dust storm generation. The upper dust cloud was transported in higher altitudes above the major clouds layer during the Trans-Pacific transport. It therefore has remained unmixed with the Asian air pollutants and almost unaffected by wet removal. The decay of its concentration level was small (only one-half after its long-distance transport crossing the Pacific). Our dust budget analysis revealed that the Asian dust flux passing through the longitude plane of 140° E was 2.1 Tg, and one third of that arrived North America. The cases analyzed in this study revealed that, while the Gobi Desert is an important source that can contribute to the long-range dust transport, the Taklimakan Desert appears to be another important source that can contribute to the dust transport occurring particularly at high altitudes.

Description: An intense dust storm occurred during 19–20 May 2007 over the Taklimakan Desert in northwestern China. Over the following days, the space-borne lidar CALIOP tracked an optically thin, highly elevated, horizontally extensive dust veil that was transported intercontinentally over eastern Asia, the Pacific Ocean, North America, and the Atlantic Ocean. A global aerosol transport model (SPRINTARS) simulated the dust veil quite well and provided a three-dimensional view of the intercontinental dust transport. The SPRINTARS simulation revealed that the dust veil traveled at 4–10 km altitudes with a thickness of 1–4 km along the isentropic surface between 310 and 340 K. The transport speed was about 1500 km/day. The estimated dust amount exported to the Pacific was 30.8 Gg, of which 65% was deposited in the Pacific and 18% was transported to the North Atlantic. These results imply that dust veils can fertilize open oceans, add to background dust, and affect the radiative budget at high altitudes through scattering and absorption. The injection mechanism that lifts dust particles into the free atmosphere is important for understanding the formation of the dust veil and subsequent long-range transport. We used a regional dust transport model (RC4) to analyze the dust emission and injection over the source region. The RC4 analysis revealed that strong northeasterly surface winds associated with low pressures invaded the Taklimakan Desert through the eastern corridor. These winds then formed strong upslope wind along the high, steep mountainsides of the Tibetan Plateau and blew large amounts of dust into the air. The updraft lifted the dust particles farther into the upper troposphere (about 9 km above mean sea level, MSL), where westerlies are generally present. The unusual terrain surrounding the Taklimakan Desert played a key role in the injection of dust to the upper troposphere to form the dust veil.

Description: The NASA space-borne Mie-lidar system CALIPSO/CALIOP revealed that multiple large Asian dust layers with a horizontal scale of 2000–3000 km reached North America, occupying the full troposphere, in April 2010. This kind of dust layer transport has not been reported before. Our analysis of CALIOP data and global aerosol model results revealed that frequent dust emissions occurred in northwestern China because of stronger-than-average near-surface winds, and that strong stable westerly winds carried the Asian dust from northwestern China to the central Pacific Ocean. A negative pressure anomaly was located in the eastern Pacific Ocean, and the main dust transport path was split into two branches: a northern path and a southern path over North America. Northern-path dust was trapped and stagnant for a longer time than southern path dust and finally subsided under a high-pressure system. Dust along the southern path reached the central US. These complex conditions resulted in a multi-layered structure of dust over North America.

Description: Simultaneous ground-based measurements of ozone (O3) and carbon monoxide (CO) were conducted in March 2005 as part of the East Asian Regional Experiment (EAREX) 2005 under the umbrella of the Atmospheric Brown Clouds (ABC) project. Multiple air quality monitoring networks were integrated by performing intercomparison of individual calibration standards and measurement techniques to ensure comparability of ambient measurements, along with providing consistently high time-resolution measurements of O3 and CO at the surface sites in East Asia. Ambient data collected from eight surface stations were compared with simulation results obtained by a regional chemistry transport model to infer recent changes in CO emissions from East Asia. Our inverse estimates of the CO emissions from China up to 2005 suggested an increase of 16% since 2001, in good agreement with the recent MOPITT satellite observations and the bottom-up estimates up to 2006. The O3 enhancement relative to CO in continental pollution plumes traversed in the boundary layer were examined as a function of transport time from the Asian continent to the western Pacific Ocean. The observed ΔO3/ΔCO ratios show increasing tendency during eastward transport events due likely to en-route photochemical O3 formation, suggesting that East Asia is an important O3 source region during spring.

Description: Three-dimensional structures of Asian dust transport in the planetary boundary layer (PBL) and free atmosphere occurring successively during the end of May 2007 were clarified using results of space-borne backscatter lidar, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and results obtained using a data-assimilated version of a dust transport model (RC4) based on a ground-based NIES lidar network. The dust layer depths and the vertical and horizontal structure simulated by RC4 agreed with those of CALIOP observations from the dust source region to the far-downstream region. Two important transport mechanisms of Asian dust in the PBL and free atmosphere were clarified: a low-level dust outbreak within the dry slot region of a well-developed low-pressure system, and formation of an elevated dust layer within the warm sector of a low-pressure system. We also represent the aging of pure dust particles using the particle depolarization ratio (PDR) at 532 nm and the color ratio (CR) at 1064 nm and 532 nm. Aerosols with high PDR were observed uniformly over the dust source region. While the dust cloud was transported to the eastern downwind regions, aerosols with low PDR and high CR occur in the layer of less than 1 km height, suggesting a mixing state of spherical aerosols and dust in the surface layer.

Description: Anthropogenic SO2 emissions increased alongside economic development in China at a rate of 12.7% yr−1 from 2000 to 2005. However, under new Chinese government policy, SO2 emissions declined by 3.9% yr−1 between 2005 and 2009. Between 2000 and 2010, we found that the variability in the fine-mode (submicron) aerosol optical depth (AOD) over the oceans adjacent to East Asia increased by 3–8% yr−1 to a peak around 2005–2006 and subsequently decreased by 2–7% yr−1, based on observations by the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA's Terra satellite and simulations by a chemical transport model. This trend is consistent with ground-based observations of aerosol particles at a mountainous background observation site in central Japan. These fluctuations in SO2 emission intensity and fine-mode AOD are thought to reflect the widespread installation of fuel-gas desulfurization (FGD) devices in power plants in China, because aerosol sulfate is a major determinant of the fine-mode AOD in East Asia. Using a chemical transport model, we confirmed that the contribution of particulate sulfate to the fine-mode AOD is more than 70% of the annual mean and that the abovementioned fluctuation in fine-mode AOD is caused mainly by changes in SO2 emission rather than by other factors such as varying meteorological conditions in East Asia. A strong correlation was also found between satellite-retrieved SO2 vertical column density and bottom-up SO2 emissions, both of which were also consistent with observed fine-mode AOD trends. We propose a simplified approach for evaluating changes in SO2 emissions in China, combining the use of modeled sensitivity coefficients that describe the variation of fine-mode AOD with changes in SO2 emissions and satellite retrieval. Satellite measurements of fine-mode AOD above the Sea of Japan marked a 4.1% yr−1 decline between 2007 and 2010, which corresponded to the 9% yr−1 decline in SO2 emissions from China during the same period.

Description: We present an aerosol data assimilation system based on a global aerosol climate model (SPRINTARS – Spectral Radiation-Transport Model for Aerosol Species) and a four-dimensional variational data assimilation method (4D-Var). Its main purposes are to optimize emission estimates, improve composites, and obtain the best estimate of the radiative effects of aerosols in conjunction with observations. To reduce the huge computational cost caused by the iterative integrations in the models, we developed an offline model and a corresponding adjoint model, which are driven by pre-calculated meteorological, land, and soil data. The offline and adjoint model shortened the computational time of the inner loop by more than 30%. By comparing the results with a 1 yr simulation from the original online model, the consistency of the offline model was verified, with correlation coefficient R 〉 0.97 and absolute value of normalized mean bias NMB 〈 7% for the natural aerosol emissions and aerosol optical thickness (AOT) of individual aerosol species. Deviations between the offline and original online models are mainly associated with the time interpolation of the input meteorological variables in the offline model; the smaller variability and difference in the wind velocity near the surface and relative humidity cause negative and positive biases in the wind-blown aerosol emissions and AOTs of hygroscopic aerosols, respectively. The feasibility and capability of the developed system for aerosol inverse modelling was demonstrated in several inversion experiments based on the observing system simulation experiment framework. In the experiments, we used the simulated observation data sets of fine- and coarse-mode AOTs from sun-synchronous polar orbits to investigate the impact of the observational frequency (number of satellites) and coverage (land and ocean), and assigned aerosol emissions to control parameters. Observations over land have a notably positive impact on the performance of inverse modelling as compared with observations over ocean, implying that reliable observational information over land is important for inverse modelling of land-born aerosols. The experimental results also indicate that information that provides differentiations between aerosol species is crucial to inverse modelling over regions where various aerosol species coexist (e.g. industrialized regions and areas downwind of them).