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

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