Abstract
We have developed a method for the direct estimation of the O3 induced HOx (OH, HO2) production rate within the atmosphere. HOx radicals produced from the reactions of O3 and ambient air constituents within a reaction tube were detected using a PERCA/LIF (PEroxy Radical Chemical Amplification/Laser Induced Fluorescence) method to measure the ROx (OH, HO2, RO2) concentration. The measured ROx concentration was found to vary as a function of the added O3 concentration. We have defined the HOx production rate as the unit concentration of O3 and unit of time (PHOx) as the slope of the measured ROx concentration at close to 0 ppbv O3 divided by the reaction time. To assess the ROx loss in our system, we performed a series of fundamental experiments based on the isoprene and ozone reaction. We compared the measured ROx concentration and the ROx concentration calculated using the MCM model (ver. 3.2) to derive the instrument function, K=0.42×[O3]0.048. The measured PHOx values are corrected according to K. To avoid variations in the PERCA signal due to natural fluctuations in the NO2 and O3 concentrations, a batch sampling method using a Tedlar bag was employed for the ambient PHOx measurements This instrument was successfully applied to measure the ambient PHOx and the ROx concentration within the Kyoto University campus for several days during July 2013. These observations demonstrated that PHOx and the ROx concentration were generally high during the daytime and low at night.
