amec CASTNET's NOy Monitoring Network Christopher M. Rogers, AMEC Kevin P. Mishoe. AMEC Melissa Puchalski, USEPA Dr. Greg Beachley, USEPA Introduction For more than 25 years, the Environmental Protection Agency's (EPA) Clean Air Status and Trends Network (CASTNET) has collected ambient measurements of nitric acid, nitrate, and ammonium concentrations using a filter pack. However, key contributors to the nitrogen budget have been missing from CASTNET, Two of these components are ammonia (NH3) and total reactive nitrogen (NOy). Missing NH3 measurements have been addressed by CASTNET's participation in NADP's Ammonia Monitoring Network (AMoN), which started in 2007. To develop a data set of NOy measurements, EPA has established an NOy monitoring network stretching from the east coast to the mountain west, which now features six EPA-sponsored CASTNET sites. In addition, NPS, a primary sponsor of CASTNET, features NO,, measurements at two of their CASTNET sites. EPA-Sponsored NOv Sites PND165 ROM206 #BVI130 #9ai16 PNF126 \ AMEC is installing an enhanced NOy monitoring system at BEL116, MD later this summer to further characterize total nitrogen. For more information, see Kevin Mishoe's talk Wednesday afternoon. Filter Pack Comparisons HN03 and particulate N03- are measured on CASTNET filter packs, and the sum is called total N03-. Because NOy is composed of HN03, particulate nitrate, and other gases and particles, a simple evaluation of the measurements is to compare the NOy concentrations with total N03- concentrations. The figures below shows comparisons of weekly average continuous NOy measurements with weekly filter pack total N03- concentrations collected at BVL130, IL. The NOy concentrations were consistently higher than the total N03- levels, as expected. The weekly total N03- concentrations, the average weekly NOy levels, and their ratios are listed for all six sites in the table below. These were calculated as the average of all valid weekly filter pack concentrations and the average of mean NOy values matching run time of the weekly filter packs. Ratios of NO., to total NO,- varied from 4.1 at BVL130 to 9.7 at BEL116, MD. Comparison of BVL130 Weekly Mean NOy and Total N03" Concentrations for 2013 Scatterplot of BVL130 Weekly Mean NOy and Total NO?" Concentrations for 2013 Summary of Total N03/NOy Measurements for 2013 Total N03 (ppb) NOy (ppb) Ratio HWF187, NY 0.2 0.7 4.3 BEL116, MD 0.8 7.4 9.7 PNF126, NC 0.3 1.5 5.3 BVL130, IL 1.2 4.4 4.1 ROM206, CO 0.1 1.2 9.5 PND165, WY 0.2 0.6 4.2 Results NOy is defined as NOx [nitrogen oxide + nitrogen dioxide] plus NOz [nitric acid, nitrous acid, peroxyacetyl nitrate (PAN), other organic nitrates, and nitrite], NOy and NO are sampled continuously and archived as 1-hour values. Typical concentrations at the six EPA- sponsored CASTNET sites measuring NOy range from an average of 0.6 parts per billion (ppb) at HWF187, NY and 0.7 ppb at PND165, WYto 4.5 ppb at BVL130, IL to 10.2 ppb at BEL116, MD, which is a suburban site. The figures to the right present composite diurnal profiles of S02, NOy, and 03 for the entire year 2013 for BEL116 and BVL130. Below and to the right are diurnal plots of NOy and 03 for HWF187 (2013), PNF126, NC (Nov-Dec 2013), ROM206, CO (Nov-Dec 2013), and PND165 (May-Dec 2013). The profiles were constructed by averaging all values from the same hour for their respective periods. The figures illustrate the geographic differences in the evolution of photochemically reactive pollutants in the lowest boundary layer. The minimum and maximum mean composite NOy and 03 are summarized in the table below. Min/Max Summary BEL116, MD BVL130, IL NOY (ppb) Ozone (ppb) Elevation (m) Min Max Min Max HWF187, NY 0.6 0.9 25 36 497 BEL116, MD 5.0 12.8 16 43 47 PNF126, NC 1.3 1.7 34 38 1216 BVL130, IL 3.3 5.8 21 41 213 ROM206, CO 0.7 1.7 43 47 2742 PND165, WY 0.5 0.7 42 49 2386 QA/QC The chart to the right shows a summary of the percent completeness of trace-level gas concentrations measured during 2013 at the six EPA-sponsored trace-level sites. For reference, the red line shows the completeness requirement of 75% for continuous S02 per QA Handbook, Vol. 11, App. D. AMEC field personnel are working internally and with the Teledyne API to improve data completeness. Operational Issues Since deployment of the Teledyne API equipment, AMEC has encountered several significant issues that have impacted data completeness. AMEC is working with the manufacturer on solutions to these issues and, over the past year and half, many have been resolved resulting in improved completeness in 2014. These include replacement of several controller boards and other components that have caused disruptions in data collection. One issue of interest is Teledyne API's use of an adaptive filter to "smooth" concentrations. While key to ambient concentrations, this feature has presented challenges to performing automated QC checks and calibrations. The figure to the right shows the differences in analyzer response with and without the adaptive filter. When not in use, the analyzer responds much more rapidly. Data Completeness for 2013 Use of Adaptive Filter HWF187, NY 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 PNF126, NC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 ROM206, CO 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 2223 PND165, WY 1 2 3 4 5 6' 9 10 11 12 13 1. 8 19 20 21 22 23 Dealing with Analyzer Drift Another operational issue that AMEC has dealt with is the drift in NOy, NO, and NPN QC check results seen at several of the NOy sites. AMEC is finding that remote calibrations and adjustments are required in between the scheduled semi-annual site visits. AMEC monitors performance of the analyzer and initiates a remote calibration when responses approach the 10% criterion for span and precision checks. The graph to the right shows an example of the drift of the NO Level 4 check. Level 4 NO QC Check Responses at BVL130 for Apr - Sep 2013 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 2223 Summary NOy data are used as part of the NCore program and provide information to atmospheric modelers, policy makers, and scientists studying environmental impacts. CASTNET now includes an eight site NOy monitoring network representing an excellent range of locations from pristine to rural to suburban. Concentrations from ROM206, CO were recently used as part of the Front Range Air Pollution and Photochemistry Experiment (FF?APPE) study. Data produced from these sites may be used in the future in the development of a SOx/NOx secondary standard. ROM406/206, CO ------- |