A study of the relationship between photochemical ozone and its precursor emissions of nitrogen oxides and hydrocarbons in Tokyo and surrounding areas

The relationship between emission intensity of (nitrogen oxides) (NOx), NC non-methane hydrocarbons (NMHC) and O3 concentration covering the Kanto area (Tokyo and surrounding prefectures) were investigated based on data analysis and model simulation. The observed trend in NOx concentration increased and the NMHC/NOx ratio and NMHC concentration decreased from 1978 to 1990. These emission changes will act to change the place where the maximum ozone is observed in the Kanto area. The fact is that the location of the daily maximum oxidant concentration has moved further from the emission areas. To clarify the temporal and areal distribution of photochemical air pollution in the Kanto area, the Urban Airshed Model (UAM) was applied. Assuming 25% decrease in NMHC and 50% increase in NOx emission intensities, simulation result showed almost the same maximum O3 value compared with the base-case simulation for 1981. On the other hand, the time when the maximum value appeared changed from 1400JST to 1600JST. Higher concentrations of oxidants were usually observed near the shore in the morning, and moved inland following sea breeze penetration. Under these meteorological conditions, the time shift obtained by the UAM simulation corresponds to the observed areal shift of the daily maximum O3 concentration.