Simultaneous multi-component measurements by MAX-DOAS in Okinawa, Japan

Since the spring of 2007, we have been making a continuous measurement by a new system based on the Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) at Cape Hedo, Okinawa, Japan (26.87N, 128.25E). Cape Hedo is a site of our planning network with the primary purpose of detecting changes of tropospheric composition, including both aerosols and trace gases. The MAX-DOAS instrument measures the ultraviolet/visible spectra of scattered sunlight at various elevation angles. The measured spectra are analyzed by a DOAS method and subsequently by a sophisticated retrieval algorithm utilizing the optimal estimation method and a Monte Carlo radiative transfer model to retrieve the vertical profile information of aerosol extinction coefficients (354 and 476 nm) and several trace gases (NO2, SO2, HCHO, CHOCHO, H2O, and O3) simultaneously. In this talk, we present our retrieval algorithm and discuss the retrieved quantities, in terms of their diurnal and seasonal variations. In addition, we show that the aerosol extinction at 476 nm was persistently high (greater than 0.2 km-1) for longer than 10 days in late July. This event is analyzed, in detail, together with MAX-DOAS trace gas data, MODIS aerosol data, a backward trajectory analysis, and a global model, to show that continental polluted airs can be transported to Cape Hedo even in summer.