| dc.description.abstract | Two-week sampling periods during the spring, summer, and fall of 2003, and the
winter of 2004 were conducted utilizing a tandem differential mobility analyzer
(TDMA) and, during the spring and summer, an aerodynamic particle sizer (APS), to
characterize the seasonal variability of the Big Bend regions aerosol optical properties.
Mass extinction efficiencies and relative humidity scattering enhancement factors were
calculated for both externally and internally mixed aerosol populations for all size
distributions collected, in an effort to possibly improve upon the default EPA mass
extinction efficiencies used for all Class 1 areas across the United States. The mass
extinction efficiencies calculated differed to some extent form the default values
employed by the EPA. Sulfate, nitrate, and light absorbing carbon (LAC) exhibited a
strong dependence on assumed mixing state, while, additionally, sulfate was also
dependent on the assumed dominant aerosol. Seasonal variability was seen with all
particle types, excluding LAC, with sulfate mass extinction efficiencies displaying the
greatest variability with season. Calculated back trajectories indicated that air masses
originating from the southeast had elevated mass extinction efficiencies, while,
conversely, air masses originating from the southwest and northwest had the smallest
mass extinction efficiencies. | en |
