Measurement of atmospheric peroxy radicals in the polluted-urban air using a chemical amplification

Abstract

In September 2001, January 2002 and December 2003, we measured peroxy radicals (RO2) in urban polluted air using the Peroxy Radical Chemical Amplification (PERCA) method. Since the observation site in 2003 was much affected by automobile exhaust, during the observatiion the average NO x concentration exceeded 90 pptv. In this observation, the daytime RO2 cancentration was similar to that at other observation sites, and in the reported literature. However, in 2003 measurement, the nighttime RO 2 concentration was found to be below the detection limit (3.5 pptv) most of the time. This result was different from the other two measurements. Though a difference was not seen in the RO2 concentration in the observations of 2001 and 2002, the average O3 concentration was very different. These results obtained in this study for urban polluted air can not be explained based on general knowledge about atmospheric chemistry, especially concerning the correlation between the RO2 and O3 concentrations.