Why Alabama?

Ever wondered why the SOAS organizers picked the study site?  Definitely a legitimate question – why are we going to Alabama?  First, the SEARCH network consists of a series of monitoring locations situated in urban and rural areas throughout the southeastern US.  Near Brent, AL is a site that is not only located in a heavily forested area, but is also at times influenced by anthropogenic emissions.  This site will serve as the primary atmospheric composition monitoring location for the SOAS study.

map

SOAS ground site location (red star) with surrounding landcover: water (dark blue), lowland forest (light blue), upland forest (green), evergreen plantation (purple), cropland and urban (yellow).

The image below provides a sample snapshot of the site selection process. Dr. Delphine Farmer, Assistant Professor at Colorado State University, is going over vegetation maps made by the Forest Service.   The edge of the circle in the map (right side/cut off) is at a 5 mi. radius from the SEARCH site as the center.

Delphine Farmer going over vegetation maps made by the Forest Service (img: Carlton)

Some other sites that we considered for this project included Ft. Leonard Wood, MO, Look Rock, NC, Coweeta, NC, and Duke Forest, NC.  But these were our rationales for picking the Alabama site:

  • It is a site with strong anthropogenic/biogenic contrasts. At times, we observe largely biogenic air masses and other times we also observe biogenic air masses that have been influenced by a range of NOx emissions.
  • Minor influence of wildfires. We have selected our experiment to be from June-July, which historically has not been a period of significant wildfire or prescribed burning activity.
  • Range of aerosol acidity conditions, due to a range of SO2 and sulfate levels. In recent years, SO2 emissions have decreased substantially in the southeast US. This site experiences a range of sulfate concentrations, but variability in aerosol acidity is not well-known.
  • To reduce confounding variables, air masses with high ammonia should be distinct from SO2 and NOx influenced air masses. There are few ammonia emission sources in this area.
  • To focus on isoprene chemistry, isolate a location with a high isoprene:terpene emission ratio. Most southeastern US locations include a mixture of conifers and deciduous trees. However, the areas immediately surrounding the site contains predominantly isoprene emitters. It is possible to situate a flux tower within a deciduous forest canopy very near to the SEARCH site.

These requirements support the science goals described in the SOAS white paper.