Vertical Structure, Transport, and Mixing of Ozone and Aerosols Observed During NEAQS/ICARTT 2004

During the 2004 New England Air Quality Study (NEAQS), which was conducted within the framework of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field experiment, airborne and shipborne lidar remote sensing instruments were deployed to characterize the 3-dimensional structure of ozone, aerosol, and low-level wind fields in the New England region. The 2004 measurements confirmed findings from the smaller-scale NEAQS 2002 experiment: the vertical structure and transport patterns of pollutant plumes from the Boston and New York City urban areas are strongly modified when they are advected over the Gulf of Maine. Because of strong vertical wind shear and a very stable atmosphere over the cold ocean water the plumes tend to get sheared apart and the resulting pieces of the plumes stay confined in layers aloft, isolated from the surface. Most notably, ozone concentrations aloft are very often significantly higher than ozone levels near the ocean surface. These elevated pollution plumes over the Gulf of Maine can affect air quality in coastal New England only when they are transported back over land. This can be accomplished by the large-scale flow or by local circulations such as the sea breeze. Once over land the elevated plumes may impact surface air quality by direct transport to higher terrain (e.g., Cadillac Mountain, ME) or by being fumigated down to the surface. Alternatively, but probably more rarely, an elevated pollution plume over the ocean may be mixed down to the surface by mechanically generated turbulence and then transported back to land within the marine boundary layer. We will use airborne and shipborne lidar remote sensing data to characterize the vertical distribution of ozone and aerosols over coastal New England, in particular the difference in plume structure over land and water. We will also show observational evidence for several of the processes described above that may mix down and transport concentrated pollution plumes aloft to coastal areas of New England.