Dr. Kanaya of the Atmospheric Composition Research Program, Frontier Research Center for Global Change, received the Chemical Society of Japan Award For Young Chemists for FY2004. The Chemical Society of Japan, a 36,000-member organization with a history of 127 years, gives the award every year to 10 or less young researchers (limited to those aged less than 35) for their outstanding research accomplishment in fundamentals and applications of chemistry. His receiving is based upon the "Elucidation of the Tropospheric Chemistry Mechanism by Measuring the OH and HO₂ Radical Concentration in the Atmosphere". In the troposphere, the OH radical is the most important "cleansing agent", whose chemical reactions initiate the transformation of many trace gases (NO_x and hydrocarbons etc.) into water-soluble species, which are then easily removed from the atmosphere. Simultaneously, the OH radical is essential in controlling the atmospheric burden of methane and O₃, both of which are the important greenhouse gases. Despite these key roles, its very low concentrations in the atmosphere had kept us away from characterizing its behavior through direct observations. Kanaya started developing a laser-induced fluorescence instrument for measuring both OH and its reservoir HO₂ in the atmosphere as a graduate student in the University of Tokyo and completed it in JAMSTEC. In the last stage of the development, much effort was put in optimizing the fluorescence detector and finally, the detection limit of as low as 2x10⁵ cm^-3 (mixing ratio of 0.008 _pptv, with 1-min. integration) was achieved. This performance is comparable to or even higher than those of the similar instruments developed by other research groups in the US, UK, and Germany.
The instrument was set up at clean remote islands (Oki, Okinawa, and Rishiri) and in Tokyo, where the OH and HO₂ concentrations were observed to study their chemical production and loss processes in detail. The observed concentration levels were compared with those predicted by a photochemical box model employing a tropospheric chemistry mechanism. At Oki and Rishiri Islands, the model significantly overpredicted the daytime HO₂ levels by up to a factor of 2, suggesting that some important processes were still missing from our current knowledge of the tropospheric chemical reactions.
Kanaya has proposed several hypotheses possibly explaining the discrepancy, including that the HO₂ radical is lost on the aerosol surfaces by heterogeneous reactions and that the OH and HO₂ radical concentrations are influenced by halogen chemistry. Particularly, IO radical, if produced via the photolysis of organoiodine species emitted from marine ecosystem (mainly by seaweeds) into the atmosphere, could react with HO₂ rapidly, influencing the concentrations of OH and HO₂. The hypothesis regarding the iodine chemistry has recently been verified by the observations in Ireland.
During the observations, it was also found that the OH and HO₂, believed to be present only during daytime when the sun provides UV photon fluxes, could be present even in the nighttime at measurable concentrations, due to the dark reactions of O₃ with olefins such as monoterpenes (C₁₀H₁₆), a class of hydrocarbons mainly emitted from coniferous forests. It is exciting to find that both marine and terrestrial ecosystems could affect the radical chemistry near the Earth's surface.
Since an observational program for atmospheric composition has not started in IORGC, the above works were conducted within FRCGC mostly supported by outside grants including "Grant-in-aid for Scientific Research" and "Research Revolution 2002"by MEXT. Kanaya mentions, "Although the atmospheric chemistry mechanisms have recently been integrated into global model simulations to predict future global warming, many parts of them are still highly uncertain. For better prediction, more observational studies are necessary to test and improve the mechanisms, especially for those related to aerosol chemistry and physics whose importance in the Earth's radiative budget has widely been recognized."