Ammonia Monitoring in the Upper Green River Basin, Wyoming

Florian M. Schwandner
Colorado State University,
Department of Atmospheric Sciences,
Fort Collins, CO USA

A 15-month ammonia air monitoring study was conducted at Boulder, Wyoming, in the Upper Green River Basin - a region experiencing rapid natural gas development with potential consequences of air quality and visibility impacts in the adjacent Class I Bridger Wilderness. The objective of this study is to characterize the local airborne nitrogen budget, specifically concentrations of ammonia and related gases and particles over one year. Samples were collected twice per week beginning December 15, 2006 and Ending May 31, 2008, using coated annular denuders and stacked filters in a URG sampler, analyzed at Colorado State University’s Atmospheric Science Department.

NH3 concentrations are variable throughout the year and below 1 ppbv for most of the monitoring period, peaking in August 2007 at 1.55 ppbv, with a yearly mean value of 0.24 ppbv. Concentrations are below or near detectable limits from December through February in 2007 and 2008. Elevated NH3 concentrations coincide with warmer summer months. A shift in ammonium nitrate equilibrium toward the gas phase might be responsible for some of this increase, although an increase in total reduced nitrogen (ammonium + ammonia) during the summer suggests that changes in emissions and or transport patterns are likely also important contributors.