Abstract
Abstract. OH reactivity is one of key indicators which reflect impacts of photochemical reactions in the atmosphere. An observation campaign has been conducted in the summer of 2007 at the heart of Tokyo metropolitan area to measure OH reactivity. The total OH reactivity measured directly by the laser-induced pump and probe technique was higher than the sum of the OH reactivity calculated from concentrations and reaction rate coefficients of individual species measured in this campaign. And then, three-dimensional air quality simulation has been conducted to evaluate the simulation performance on the total OH reactivity including "missing sinks", which correspond to the difference between the measured and calculated total OH reactivity. The simulated OH reactivity is significantly underestimated because the OH reactivity of volatile organic compounds (VOCs) and missing sinks are underestimated. When scaling factors are applied to input emissions and boundary concentrations, a good agreement is observed between the simulated and measured concentrations of VOCs. However, the simulated OH reactivity of missing sinks is still underestimated. Therefore, impacts of unidentified missing sinks are investigated through sensitivity analyses. In the cases that unknown secondary products are assumed to account for unidentified missing sinks, they tend to suppress formation of secondary aerosol components and enhance formation of ozone. In the cases that unidentified primary emitted species are assumed to account for unidentified missing sinks, a variety of impacts may be observed, which could serve as precursors of secondary organic aerosols (SOA) and significantly increase SOA formation. Missing sinks are considered to play an important role in the atmosphere over Tokyo metropolitan area.
Highlights
Air quality in Japan has been improved, some problems are still remained unresolved
To validate the simulations in terms of photochemical reactions, we have examined whether the simulation can reproduce the measured total OH reactivity including missing sinks
We have developed a three-dimensional air quality simulation framework which consists of the Weather Research and Forecasting (WRF) model for meteorology, the Community Multi-scale Air Quality (CMAQ) modeling system for pollutant concentrations, and emission inventory models
Summary
Air quality in Japan has been improved, some problems are still remained unresolved. Total OH reactivity is one of key indicators which reflect the impacts of identified and unidentified species on photochemical reactions and secondary products It is useful as an indicator to validate the three-dimensional air quality simulations in terms of complex photochemical reactions. We have conducted sensitivity analyses to investigate the impacts of missing sinks on photochemical reactions and secondary products. Total OH reactivity was measured at New York City (Ren et al, 2003), Mexico City (Shirley et al, 2006), Mainz (Sinha et al, 2008), and Guangzhou (Hofzumahaus et al, 2009) Most of these studies have implied existence of missing sinks in the atmosphere.
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