A comparison of AMoN measurements with localized, arrayed passive NH3 samplers in Northern Utah

Randy Martin1 and Munkh Baasandorj2

In 1983, the National Atmospheric Deposition Program (NADP) established a National Trends Network (NTN) monitoring location in Utah’s Cache Valley (UT01) and the data have consistently shown wet deposition of ammonium (NH4+) among the highest in the nation.  Several airsheds in the region have been promulgated as PM2.5 non-attainment and the largest mass fraction of the local PM2.5 is most often ammonium nitrate (NH4NO3).  Denuder measurements at the Logan, UT regulatory site in 2003-04, found winter and summer NH3 concentrations averaged 9.2 ± 2.3 and 3.7 ± 0.4 µg/m3, respectively.  In the winter and summer of 2006, an array of 25 passive samplers was deployed throughout the Cache Valley for three different sample periods during each season.  The winter and summer valley-wide NH3 concentrations averaged 28.1±5.1 and 22.9±5.2 µg/m3, respectively.  More recently, during January and February of 2016, a slightly smaller version of the passive array was repeated in the Cache Valley, parallel to a study along the Wasatch Front, wherein 10 samplers were deployed at many of the same locations as the 2006 study for seven periods.  The spatial concentration contours from this study were found to be very similar to the previous study.  However, the valley-wide average NH3 concentrations were significantly greater with an overall average of 106 ± 22.7 µg/m3.  For comparison, the Wasatch Front NH3 concentrations averaged 14.2 ± 2.0 µg/m3.

The UT01 location was updated in 2011 to be a part of the NADP’s Ammonia Monitoring Network (AMoN).  At the same a site (UT97) was established in the Salt Lake valley.  In support of the NTN measurements, the AMoN data consistently indicated that the Cache Valley location had among the highest gas-phase NH3 measurements in the USA.  UT01’s annual average NH3 concentrations for 2012, 2013, and 2014 were 15.0 ± 1.7, 18.7 ± 1.9, and 15.8 ± 2.3 µg/m3, respectively.  During the same time period, UT97’s annual average concentrations were 4.0 ± 0.5, 3.9 ± 0.6, and 4.5 ± 0.4 µg/m3, respectively

  It is of interest to note that the data from UT01 are often flagged with the QR code “B”, meaning the data are valid but with minor problems.  The site is located on a Utah State University research farm and small quantities of livestock are often within the given boundary.  This presentation will examine the siting both UT01 and UT97 as to its representativeness of the given airsheds.


1Utah State University, randy.martin@usu.edu
2Utah Division of Air Quality, mbaasandorj@utah.gov