Journal of Geophysical Research Atmospheres · 2000 · 67 citations · 72 references
Radical EmissionEnvironmental MonitoringEngineeringAir Pollution MeasurementAtmospheric PhotochemistryAir QualityMarine ChemistryPollution MonitoringChemistryEnvironmental PhotochemistryEarth ScienceEnvironmental ChemistryRadical ConcentrationAtmospheric ScienceSummer 1998Environmental Analytical ChemistryOki IslandAnalytical ChemistryChemical MeasurementPhotochemistryDetection LimitAtmospheric ConditionEnvironmental AnalysisAir PollutionHo 2
The daytime variation of hydroperoxy (HO 2 ) radical concentration was observed by an instrument based on laser‐induced fluorescence with NO addition at Oki Island, Japan, in July/August 1998. Although OH was not detected due to the high detection limit of the instrument, HO 2 was determined with the detection limit of 0.8 parts per trillion by volume (pptv) (S/N = 2, integration time of 1 min). On average, HO 2 showed a maximum concentration of around 9 pptv in the early afternoon hours. During the field campaign, chemical species and meteorological parameters such as O 3 , CO, nonmethane hydrocarbons(C 2 ‐C 6 ), NO/NO 2 , HCHO/CH 3 CHO, SO 2 , HNO 3 and J (NO 2 ) were also observed. Unfortunately, the absolute value of J (O 1 D ) was not measured. Model calculations for radical concentrations were performed and they were compared to the observed hourly HO 2 concentrations. On August 9 the calculated HO 2 matched the observation very well within the uncertainties of observations (±26%, 1σ) and the model (±24%, 1σ). This indicates a good performance of model calculations in estimating HO 2 under certain conditions with plenty of isoprene. On other days, however, model usually overestimated HO 2 by a factor of 2, especially in the hours around noon. It is deduced that some important HO x loss chemistry is missing in the model. Although the cause of the discrepancy is not fully understood, possible mechanisms to explain the overestimation are studied. A hypothesis with additional loss of HO 2 would be more plausible than that with additional OH loss. The additional loss rate for HO 2 that can reduce the calculated HO 2 to the measured level was computed for each hour. Its variation correlated well with those of H 2 O and some photochemical products. The possibilities of HO 2 loss on aerosol surface, unknown acceleration of HO 2 reactions in the presence of high H 2 O, and HO 2 reactions with carbonyl species are discussed.
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