Peroxy radicals (hydroperoxy HO2 and organic peroxy RO2) play important roles in the photochemistry of troposphere. They are involved in the production and removal of ozone in the photochemical cycles and are closely related to atmospheric hydroxyl (OH) radical budget. In this work, a dual-channel peroxy radical chemical amplification (PERCA) instrument using diode laser cavity ring down spectroscopy (CRDS) is developed for measurements of the peroxy radicals. The ambient air is sampled into an amplification channel and a reference channel. In the amplification channel, HO2 and RO2 are first converted to NO2 via reactions with an excess amount of NO, and the OH and RO coproducts are recycled back to HO2 in subsequent reactions with an excess amount of CO and O2; the chain reactions of HO2 are repeated and amplify the level of NO2. The reference channel is for the background NO2 and O3. The NO2 concentrations from both channels are monitored simultaneously by two CRDS systems. The concentration of the amplified NO2 from HO2 and RO2 is determined as the difference between the amplification and the reference channel. The optimized amplification factor of the dual-channel PERCA-CRDS system is 180, calibrated using laboratory generated HO2 and CH3O2 radical sources. The detection sensitivity is shown to be ~4 ppt/10s (3s).  The results from ambient studies and environmental chamber studies will be discussed.

Measurements of peroxy radicals using dual-channel chemical amplification-cavity ringdown spectroscopy

243rd National Meeting (2012)

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