Atmospheric Transport of PM. Transport Mechanisms Influence of Transport on Source Regions Plume Transport Long Range Transport Resource Links. Contact: Rudolf Husar, [email protected] Transport Mechanisms.
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The three major airmass source regions that influence North America are the northern Pacific, Arctic, and the tropical Atlantic. During the summer, the eastern US is influenced by the tropical airmass, from Gulf of Mexico.
The three transport processes that shape regional dispersion are wind shear, veer, and eddy motion. Homogeneous hazy airmasses are created through shear and veer at night followed by vigorous vertical mixing during the day.
Low wind speeds over a source region allows for pollutants to accumulate. High wind speeds ventilate a source region preventing local emissions from accumulating.
In urban areas, during the night and early morning, the emissions are trapped by poor ventilation. In the afternoon, vertical mixing and horizontal transport tend to dilute the concentrations.
Plume transport varies diurnally from a ribbon-like layer near the surface at night to well mixed plume during the daytime.
Even during the daytime mixing, individual power plant plumes remain coherent and have been tracked for 300+ km from the source.
Most of the plume mixing is due to nighttime lateral dispersion at night followed by daytime vertical mixing.