Itaru Sano

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.

Aerosol retrieval based on combination use of POLDER and GLI data

This work proposes an approach to retrieve aerosol properties based on combination of multi-sensor data. Here both data provided by POLDER (Polarization and Directionality of Earth Reflectances) and GLI (Global Imager) mounted on Japanese satellite ADEOS-2(Advance Earth Observing Satellite-2), which was operating during April to October in 2003, are examined. POLDER sensor has such a unique facility as directional polarization measurements with three channels, and GLI provides high-resolution images over the wide range of wavelength from near ultra violet to the thermal infrared. This fact looks promising that combining both sensor data presents effective information of aerosols. A proposed algorithm for aerosol retrieval over the land, in addition to forgoing POLDER oriented procedure, involves following processes as: 1) classification of non-absorbing and absorbing aerosols based on GLI data in the near ultra violet and the violet channels. 2) a forgoing POLDER oriented procedure. 3) atmospheric correction for NDVI.

Atmospheric correction for land observing sensor AVNIR-2

An algorithm for atmospheric correction of space based data given by AVNIR-2 sensor mounted on the land observing satellite ALOS is described here. Our procedure is based on the multiple scattering calculations in an Earth atmospheresurface system. The atmospheric constituents are roughly divided into gas molecules and aerosols. It is well known that the aerosol characteristics vary with time and place. This fact indicates that an aerosol retrieval problem should be solved before atmospheric correction of satellite data. Accordingly the atmospheric correction is treated step by step in this work. At the first step, atmospheric correction by gas molecules alone, what one calls Rayleigh correction, is considered. Then Rayleigh correction including the Earth surface height is dealt with. Finally atmospheric correction by both of gas molecules and aerosols is taken into account. In this phase, the aerosol properties are retrieved from the ground-based AERONET (Aerosol Robotics Network) data. The processed images after atmospheric correction according to the above three steps are compared with one another. It is shown that our atmospheric correction presents the improved satellite images.

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.

Atmospheric particles over an urban area

For monitoring of urban atmospheric particles, simultaneous measurements of aerosols and suspended particulate matter (SPM) have been undertaken at Kinki University Campus, Higashi-Osaka, Japan, since 2004. The relationship between PM2.5 concentrations and aerosol properties obtained from radiometry using a multi-spectral photometer located as a NASA/AERONET station is examined in this work. It is found a linear correlation between aerosol optical thickness and PM2.5 concentrations for both ordinary days and days with dust events. This fact indicates that aerosol characteristics can be estimated from SPM data, and vice versa. Combining radiometric aerosol information with surface-level particulate mass measurements is useful in studying air quality and aerosol properties. It is of interest to mention that the largest dust event recorded among our long-term observations was detected during the spring of 2006.