Atmospheric Transport of PM

1. Atmospheric Transport of PM Transport Mechanisms Influence of Transport on Source Regions Plume Transport Long Range Transport Resource Links Contact: Rudolf Husar, rhusar@mecf.wustl.edu

2. Transport Mechanisms • Pollutants are transported by the atmospheric flow field which consists of the mean flow and the fluctuating turbulent flow 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.

3. Influence of Transport on Source Regions Horizontal Dilution Vertical Dilution 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.

4. Plume Transport • Much of the man-made PM2.5 in the East is from SO2 emitted by power plants. 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.

5. Long Range Transport • In many remote areas of the US, high concentration of PM2.5 have been observed. Such events are have been attributhe Long range • Long range transport events occur when there is an airmass stagnation over a source region, such as the Ohio River Valley and the PM2.5 accumulates. Following the accumulation, the hazy airmass is transported to the receptor areas. • Satellite and surface observations of fine particles in hazy airmasses has provides a clear manifestation of long range pollutant transport over Eastern N. America.

6. Resource Links • Workbook Table of Contents • Comment and Feedback Page • Applications / Reports • Data sets used in the Applications • Methods and tools used in the Applications