In Session 5 we also discussed smaller scale flow. For example, pollutants that are emitted near the ocean or large body of water (many factories are near large water sources) may be blown inland during the day due to the formation of a sea breeze. At night, the reverse may occur due to the land breeze. Possibly most importantly, we learned about the microscale flow of air due to obstructions and surface heating. These small scale motions lead to the development of turbulent eddies that increase friction in the lower atmosphere and affect pollution transport away from the source. And what about pollution in urban areas? We discussed urban flow and its complexity. For example, pollution will accumulate in high concentrations on the lee side of a building in a closed circulation cavity.
Numerical models have only recently been able to accurately simulate flow patterns on the mesoscale level. Microscale simulations are currently too complex for any models to simulate. It is necessary to realize that the flow patterns around buildings and through street canyons are too small for models to predict effectively. Currently, models lump urban areas together and treat them as a single body. In the future, researchers may develop numerical models that can be useful on the smallest levels. However, there are numerical models that are used for the purpose of simulating pollutant dispersion from a factory smoke stack. Such models have become very useful in the air quality community.
Finally, we learned a little about how model grids work and the importance of a practical grid size for meteorological models. Naturally, this is also important for air quality models, as many of them work on the same principles. In the next session, we will take atmospheric motion to another level and discuss stability, which has an enormous impact on the vertical transport and dispersion of pollutants.
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