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 RO₂ 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.