Ammonia and Ammonium Measurements from the Southeastern U. S.
Rick D. Saylor
Atmospheric Research & Analysis, Inc,
Snellville, GA USA
The Southeastern Aerosol Research and Characterization (SEARCH) study was designed and implemented in 1998-1999 in an effort to provide extensive long-term data on the sources and chemical characteristics of atmospheric particulate matter (PM) and gaseous precursors in the southeastern U. S. The SEARCH network is comprised of eight monitoring sites arranged into four urban (or suburban)/rural pairs located in four states in the southeast (Georgia, Alabama, Mississippi and Florida). Routine measurements at SEARCH sites include continuous trace gases (O3, SO2, CO, NO, NO2, HNO3 and NOy), surface meteorology, daily 24-hr integrated filter-based fine and coarse PM mass and composition, as well as semi-continuous PM2.5 mass and composition (including SO42-, NO3-, NH4+, organic and elemental carbon, and soil-derived components). Since 2004, gaseous ammonia (NH3) has been measured on a 24-hr integrated sampling schedule by citric acid impregnated annular denuders at all eight sites in the SEARCH network. Additionally, since mid-2007, continuous measurements of NH3 with a 5-minute temporal resolution have been made at three SEARCH sites (one urban [Atlanta, Georgia] and two rural [Yorkville, Georgia; Oak Grove, Mississippi]). The paper will present analyses of 24-hr integrated denuder-based NH3 measurements collected since 2004, as well as investigations of data from the recently initiated continuous NH3 instrument. Trends of NH3 in the southeast U.S. since 2004 will be examined and analyses of individual high NH3 concentration episodes will be presented. The importance of local confined animal feeding operations (CAFOs) as sources of NH3 will be demonstrated and analyses will be presented to investigate the possible processes that contribute to distinctive diurnal profiles that are observed at the urban/rural site pair in Georgia.