Observation of the primary NO2 and NO oxidation near the trunk road in Tokyo

By the reinforcement of the vehicle emission reduction requirement in Japan, the nitrogen oxides (NOx) concentration in a roadside atmosphere decreased clearly recently. However, the ambient nitrogen dioxide (NO2) concentration does not show a substantial decrease.For the forecast of the improvement of the roadside NO2 by the motor vehicle emission regulation, we have been developing a roadside air quality simulation model. The chemical reactions of nitrogen oxide (NO) oxidation with ozone (O3), photodissociation of NO2, and O3 formation were included in this model. This study was carried out to clarify the NO2 behavior near roadside. Involving a spatial distribution of O3 concentration measurement, temporal and spatial variation of NO and NO2 was measured by the devices of chemiluminescence method which were prepared for each species. Concentration change was measured at the same time in four sites every 1 s to pay attention to a percentage of NO2/NOx which varied from route neighborhood to lee side way. The air flow of each sites was monitored by the ultrasonic 3D anemometer. The effect of NO2 concentration change due to the air stagnation or background ozone concentration was evaluated.From the cycle variation of potential ozone (PO) concentration as a function of the elapsed time of the traffic signal, the direct exhaust NO2 was estimated, and, around Noge intersection of Ring 8, Tokyo, 7.3% was obtained as primary NO2 fraction from vehicles. During an advection from the curbside site (0 m) to the 20 m remote site, more than 40% of NO oxidized and generate NO2 at 10 m height. At 3 m height, 7% of NO2 was generated and O3 was consumed in same quantity at the same time.