A field measurement was conducted at the center of Tokyo metropolitan area in the summer, 2007. Total OH reactivity and concentrations of NOx, CO, O3, individual non-methane hydrocarbons (NMHCs) and oxygenated volatile organic compounds (OVOCs) were observed. Observation data obtained in this measurement was used to validate the 3-D air quality simulation.

We executed the 3-D air quality simulation with WRF-CMAQ to simulate pollutant concentrations for the period of the measurement. SAPRC99 was used for the chemical mechanism. Most of individual VOC species are lumped into several surrogate groups. Concentrations of each species and surrogate groups were compared with simulation results. Concentrations of heavier surrogate groups like ALK5 and ARO2 in SAPRC99 were mostly overestimated.

It must be noted that all of species lumped into heavier surrogate groups cannot be identified. Some unknown species may be omitted in emissions and/or observations. Influences of unknown species can be estimated from total OH reactivity. It is known that there is a gap between total OH reactivity and sum of OH reaction rates of identified VOC species, which is called missing sinks. Missing sinks correspond to unknown primary emitted species as well as secondary products from photochemical reactions. Secondary products are treated in the 3-D air quality simulation as surrogate groups. We investigated influences of unknown primary species and secondary products in terms of OH reactivity through sensitivity analyses in the simulation. It was found that they especially influence on secondary organic aerosol formation.

Underprediction of organic carbons is one of common issues in the 3-D air quality simulation. This study shows that unknown primary/secondary VOC species are important for organic carbons. The OH reactivity is powerful tool to estimate influences of unknown species.