A study on the impact of mountainous terrain on transboundary and local pollution

The area around the Japanese Alps, which is the focus of this study, is located at the center of Japan's main island and surrounded by mountains with multiple basins. Here, we investigated the effect of mountains on aerosol blocking with respect to transboundary pollution and estimated the effect of the mountain source with respect to local pollution using observations and simulations. A regional chemical transport model was employed for the study. To investigate the effect of mountains, simulations were conducted with and without mountains. From the results of these simulations, we estimated the mountain effects. The presence of mountains was found to increase or decrease aerosol concentration in some cases. However, when averaged over the simulation period, the results showed that mountains effectively reduce aerosol concentrations. On the days when aerosol concentrations increased due to the mountain effect, meteorological conditions with high local emissions and the basin effect acted synergistically to accelerate the increase in aerosol concentrations.