Diagnosis of urban air quality by measurement of total OH reactivity

Comprehensive observations in the suburbs of Tokyo

Abstract

Total OH reactivity was measured by use of a laser-induced pump and probe technique in order to diagnose comprehensively the urban air quality in the suburbs of Tokyo. The concentrations of NO_xCO, O₃, NMHCs (non-methane hydrocarbons) and OVOCs (oxygenated volatile organic compounds) were observed simultaneously. The observations were conducted in July and August 2003, and in January and February 2004. The measured OH loss rates were usually higher than the calculated values, this was derived by using the measured concentrations of the trace species. The difference between the measured and calculated values in the summer observation was approximately 25 %. However, for the winter observation, the difference between the measured and calculated values was less than the difference between the summer values. In addition, while the difference observed in the summer correlated with the concentration of 0₃, no correlations were confirmed in the winter. This suggests that the secondary products of the photochemical reactions in the atmosphere would be a missing sink for the OH loss process.