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Abstract:

Tropospheric ozone, a major component of photochemical oxidant, has been the focus of attention as an air pollutant of concern for its effects on health and vegetation and also as a short-lived climate forcer (SLCF) along with methane and black carbon (BC). Computational simulations with atmospheric chemistry models are used for quantitative assessment of the environmental and climate impacts of ozone. The accuracy of the assessment depends on the quantitative accuracy of the chemistry model. 

Ozone is produced secondarily through tropospheric photochemistry whose core is a HO_x cycle mechanism formed by propagation reactions of OH, HO₂ and organic peroxy radicals (RO₂). It has been suggested that the HO_x cycle includes two processes being potential sources of error in ozone prediction. One is the heterogeneous uptake process of peroxy radicals (HO₂ and RO₂) onto clouds and aerosols, and the other is the reaction of OH radicals with unidentified and/or difficult-to-measure species. In both cases, the evaluation of ozone production may change by up to tens of percent with or without consideration according to the situation, and their incorporation into tropospheric ozone chemistry models remains a challenge. 

Our group developed a laser spectroscopy-based HO_x reactivity measurement system which enable us to quantitatively verify the heterogeneous uptake process of peroxy radicals onto clouds and aerosols by determining kinetic parameters, and also to investigate the sources of unidentified and difficult-to-measure OH reactive species through atmospheric observations and environmental chamber experiments. I will introduce a basic idea of the HO_x reactivity measurement system and recent findings relating to the ozone formation chemistry in this seminar.

Key words: Laser induced fluorescence, Uptake coefficient, unknown OH reactivity, photo chemical oxidant, HO_x cycle.