Makiko Mukai

A study of anthropogenic impacts of the radiation budget and the cloud field in East Asia based on model simulations with GCM

[1] We investigated the effects of man-made air pollutants on the climate of East Asia, focusing on eastern China where anthropogenic aerosol concentrations are rapidly increasing. The increasing emission of anthropogenic aerosols causes serious air pollution episodes and various effects on the climate in this region. It is therefore necessary to quantify the contribution of aerosols to the change in the radiation budget and the cloud field. Our purpose of this study is to evaluate the sensitivity of anthropogenic aerosols and other anthropogenic factors such as greenhouse gas (GHG) upon the radiative forcing. Then an aerosol transport model coupled to a general circulation model and an ocean mixed-layer model was used to investigate the relationships among the anthropogenic aerosol forcing, GHG forcing, surface radiation budget, and cloud field. Our simulation results showed that copious anthropogenic aerosol loading causes significant decrease in the surface downward shortwave radiation flux (SDSWRF), which indicates that a direct effect of aerosols has the greatest influence on the surface radiation. It is found from our model simulations that low-level clouds increase but convective clouds decrease due to reduced convective activity caused by surface cooling when anthropogenic aerosol increases, and GHG increase has an insignificant effect on SDSWRF but a significant effect on the cloud field. In other word model simulations suggested that the aerosol forcing mainly causes a reduction of SDSWRF, whereas the change in the cloud field is influenced both anthropogenic aerosol and GHG effects. Thus this work demonstrated with sensitivity experiments the importance of aerosols to cause significant climate effects in the East Asian region, though further study is needed because our study is based on results from one specific model and limited data analysis.

Errata: Suspended particulate matter sampling at an urban AERONET site in Japan, part 2: relationship between column aerosol optical thickness and PM2.5concentration

The concentration of suspended particulate matter smaller than 2.5 μm (PM 2.5) was linearly correlated with the column aerosol optical thickness (AOT) based on simultaneous measurements at a NASA/AERONET station at Kinki University Campus, Higashi-Osaka, Japan, between March 2004 and June 2006. The correlation coefficient differed with the aerosol type, being maximal when PM 2.5 values were measured 120 minutes after AOT data for a dust episode, but almost independent of the time difference between measurements for anthropogenic aerosols. The obtained results were validated using data obtained at the Higashi-Osaka and Noto sites. Our results suggest that the PM 2.5 mass concentration can be estimated from the AOT, and vice versa, and hence a distribution map of PM 2.5 can be produced from the satellite-derived AOT map determined from the Aqua/MODIS sensor.

Suspended particulate matter sampling at an urban AERONET site in Japan, part 1: clustering analysis of aerosols

The aerosol properties of urban atmospheric particles have been analyzed for radiometry data obtained using a multi-spectral photometer located at a NASA/AERONET station at Kinki University Campus, Higashi-Osaka, Japan, since 2002. The suspended particulate matter has been simultaneously measured at the same AERONET site since 2004. Our measurements and a clustering analysis reveal the aerosol types over the industrial city of Higashi-Osaka. It is shown that aerosols at Higashi-Osaka can be classified into three categories: (1) ordinary, which represents the background clear atmosphere of Higashi-Osaka, (2) anthropogenic aerosol events, and (2) dust episodes called Kosa, when large amounts of soil dust are transported to Higashi-Osaka from the Chinese mainland on westerly winds, especially in spring. We also found that the linear correlation exists between column aerosol optical thickness and PM2.5 concentration, and the correlation is better within each aerosol cluster than overall.

Evaluation of air quality from space

The relationship between concentration of suspended particulate matter (PM2.5) and column aerosol optical thickness (AOT) is examined based on the simultaneous measurements at a NASA/AERONET station at Kinki University Campus, Higashi-Osaka, Japan since March in 2004. We drew the following results: 1. A strong linear correlation exists between PM2.5 and AOT, 2. The correlation is better within each type of aerosols as anthropogenic type and dust type than overall, 3. The correlation coefficients take the highest value in such a case that PM2.5 values are measured in 30-minutes behind after AOT data. These facts are explained with the model simulations. Our results highlight the possibility that the PM2.5 concentration can be estimated from the AOT, and vice versa. Moreover, combining radiometric aerosol information with surfacelevel particulate mass data appears to be a promising approach for gaining a better understanding of air quality and the atmospheric environment.

Improvement of PM2.5 analysis by using AOT and lidar data

Concentration of suspended particulate matter less than 2.5 μm (PM2.5) is a representative parameter of air quality. Simultaneous measurements of PM2.5 and the column aerosol optical thickness (AOT) have been performed at a NASA/AERONET station, Higashi-Osaka, Japan since March 2004. They successfully provide a linear correlation between PM2.5 and AOT. A Mie scattering lidar instrument was deployed at the same observational site in April, 2008. It provides us with the attenuated backscattering coefficients of aerosols at wavelengths of 0.532 and 1.064 μm, which indicate the vertical distribution of aerosols. This work intends to improve the correlation between AOT and PM2.5 by using the measurements of lidar.

Synthetic monitoring of Asian dust from space, ground and/or simulations

It is well known that the heavy soil dust has been transported from the China continent to Japan on westerly winds, especially in spring. It is also known that the increasing emissions of anthropogenic aerosols associated with continuing economic growth in Asia has caused serious air pollution over the wide range of East Asia. Accordingly the dust particles involve anthropogenic aerosols as well as soil dust. Thus aerosols in Asia are very complex due to mixing of small anthropogenic particles and large dust particles, which are called Asian dust. The satellite observation is an effective tool for global monitoring of the Asian dust. A new algorithm for detection of Asian dust from space is proposed based on the multispectral satellite (Terra/Aqua/MODIS) data. The derived space-based results are validated with the ground-based measurements and/or model simulations. The sun/sky photometry has been undertaken at NASA/AERONET stations at Higashi-Osaka in Japan, where the suspended particulate matter (SPM) sampling and NIES/LIDAR network equipment have been simultaneously working. In order to validate the satellite results with these surface-level data, an aerosol transportation model is available. In other word, the space-based and/or surface-based measurements are examined with the model simulations, and vice-versa.

Estimation algorithm for aerosol properties from CAI on GOSAT

Green house gases observational satellite (GOSAT) was successfully launched on 23 January in 2009 by JAXA. The satellite carries two sensors, Fourier Transform Spectrometer (FTS) and Cloud Aerosol Imager (CAI). The CAI has four observing wavelengths as 0.38, 0.67, 0.87 and 1.6 μm. It is shown here that this CAI/0.38μm is a unique observing band among usual sensors as MODIS and so on, and it is useful to distinguish the aerosol characteristics of absorbing (e.g., biomass burning) or non-absorbing (e.g., sulfate). In other word, this work proposed a space based retrieval algorithm for atmospheric aerosols including estimation of the optical constant for biomass burning particles. Our algorithm aims to apply the combination use of near UV data with GOAT/CAI, the violet data with Aqua/MODIS and near-IR polarization data with PARASOL/POLDER. In practice the algorithm has been partly examined by using ADEOS-2 / GLI data.

Evaluation of seasonal change of aerosol properties from satellite and simulations

A wide variety of aerosols are suspended in the atmosphere. Especially in East Asia, a huge amount of fossil fuel burning aerosols are emitted throughout the year. Further it seems that the characteristics of aerosols change with the season, and hence the influence impact of aerosols over the climate also varies according to the season. Thus an accurate estimation of seasonal aerosol properties is an urgent subject on the global climate problem. This work is based on the Moderate-resolution Imaging Spectroradiometer (MODIS) data and the simulation results with a three-dimensional aerosol transport-radiation model. It is of interest to mention that aerosol distribution explicitly shows the seasonal change. For example, aerosol concentration in summer is larger than that in winter from eastern China to Japan. This result is drawn from both MODIS data and model simulations. The model simulations suggest that the seasonal change is due to the variations in the photochemical reaction process and transportation process. MODIS data shows that the sulfate aerosols are much more dominant in summer than those in winter at Beijing which is influenced strongly by fossil fuel burning aerosols. This fact is also supported by model simulations. From the present study I can draw such a result in respect of surface radiation budget as the aerosol impact on the reduction of solar radiation is more dominant in summer than that in winter in East Asia.

Seasonal Change In Aerosol Effects In China Simulated By General Circulation Model

This study intends to investigate the seasonal change in anthropogenic aerosol effects in China, where anthropogenic aerosol are increasing with fossil fuel consumption increase, upon the climate change by the aerosols interacting with the radiation budget. For this purpose, we used an aerosol transport model coupled to a general circulation model. Our simulated results show significant seasonal variation between summer and winter aerosol optical thickness and the seasonal variation influences the aerosol effects on surface radiation. Aerosol direct and indirect effects are greater in summer than in winter due to large aerosol loading in summer especially in Northern China. In the other hand, the seasonal change in aerosol effects is small in Southern China. Because aerosol direct effect is slightly larger in winter and aerosol indirect effect is larger in summer. It is thought that the more noticeable amount of cloud is larger in summer over China.

Fine mode aerosols on a global scale

The retrieval algorithm for aerosol remote sensing has still some problems to be solved. For example, miss-leading of aerosol type selection has often happened due to the difficulties to detect the absorbing aerosols, such as carbonaceous and dust aerosols, over land. The POLDER polarization data are useful to estimate the aerosol information even over land region. This work intends to modify the satellite retrieval procedure by combining the model simulations. The result of numerical simulations is used as a priori information of existence of absorbing aerosols in the atmosphere. Our procedure, in practice, is applied to the POLDER observation period in April, 1997. As results, aerosol optical thickness at three wavelengths are retrieved, and then they are applied to estimate the mass concentration of fine mode aerosols based on the relationship between AOT by ground based sun photometry and PM2.5 sampling. It is found that in April of 1997 the bio-mass burning aerosols are heavily loaded over South East Asia.