Effects Of Topography On Air Motion

Topography can affect micro- and mesoscale air motion near point and area sources. Most large urban centers in this country are located along sea (New York City and Los Angeles) and lake (Chicago and Detroit) coastal areas, and heavy industry is often located in river valleys, e.g., the Ohio River Valley. Local air flow patterns in these regions have a significant impact on pollution dispersion processes. For example, land-water mesoscale air circulation patterns develop from the differential heating and cooling of land and water surfaces. During the summer when skies are clear and prevailing winds are light, land surfaces heat more rapidly than water. The warm air rises and moves toward water. Because of the differences of temperature and pressure, air flows in from the water, and a sea or lake breeze forms. Over water, the warm air from the land cools and subsides to produce a weak circulation cell. At night, the more rapid radiational cooling of land surfaces results in a horizontal flow toward water, and a land breeze forms (Godish 1991).

Air flows downhill into valley floors, and the winds produced are called slope winds. As the air reaches the valley floor, it flows with the path of the river. This air movement is called the valley wind. The formation of valley wind lags several hours after slope winds. Because of a smaller vertical gradient, downriver valley winds are lighter and because of the large volume, cool dense air accumulates, flooding the valley floor and intensifying the surface inversion that is normally produced by radiative cooling (Godish 1991). The inversion deepens over the course of the night and reaches its maximum depth just before sunrise. The height of the inversion layer depends on the depth of the valley and the intensity of the radiative cooling process.

Mountains affect local air flow by increasing surface roughness and thereby decreasing wind speed. In addition, mountains and hills form physical barriers to air movement.

In summary, the atmospheric dispersion of air pollution emissions depends on the interplay of a number of factors which include (1) the physical and chemical nature of the pollutants, (2) meteorological parameters, (3) the location of the source relative to obstructions, and (4) downwind topography (Godish 1991).

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

Get My Free Ebook


Post a comment