GUIDELINE SERIES
OAQPS NO. 1.2-075
OOOR77004
GUIDANCE FOR THE FUTURE USE OF NASN
(This Guideline replaces OAQPS #1.2-020)
VS. ENVIRONMENTAL PROTECTION AGENCY
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina
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GUIDANCE FOR THE FUTURE USE OF NASN
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OAQPS #1.2-075
| (This guideline replaces OAQPS f1.2-020)
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I Jun&, 1977
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I Monitoring and Data Analysis Division
Research Triangle Park, N.C.
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BACKGROUND
Over the past year, The Standing Air Monitoring Work
Group (SAMWG) developed a series of monitoring issue papers
for the criteria pollutants which formed the basis of the
Air Monitoring Strategy for SIP's. The purpose of the
air monitoring strategy analysis was to present recommen-
dations for an improved and more efficient national monitoring
system that could provide timely and accurate data to meet
the priority needs of EPA and the State and local agencies.
Several Regions have asked for clarification regarding
integration of the NASN into the ambient monitoring program
discussed in the draft Air Monitoring Strategy Document.
Therefore, we have prepared the following material which
should be used by the Regions in their evaluation of State
and local monitoring programs. This material should be used
during the negotiations with State agencies in the development
of the State monitoring plan required under the Regional
Operational Guidance output for monitoring. The memorandum
"Implementing SAMWG Recommendations," April 22, 1977 from
E.F. Tuerk to Deputy Regional Administrators, describes
the accomplishments which must be addressed in the monitoring
plan. Several of these accomplishments deal with the desig-
nation of SLAMS/NAQTS networks., The guidance described
below describes how the existing NASN sites are to be considered
during the negotiation/designation process. This guidance should
be considered as a replacement for OAQPS #1.2-020, "Guidance
for Decentralization and Continued Operation of the NASN,"
September, 1974.
INTRODUCTION
In the past, data from the NASN network formed the sole
basis for EPA to perform national SO-, TSP and N02 air quality
trends analysis. However, with the rapid increase in State
and local monitoring activities in the last seven years,
sufficient air qualty data (in terms of geographical and time
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coverage) exists so that EPA no longer needs to rely on the
NASN as the only source of trends data.
For SO- and N02, methodology problems have substantially
diminished the usefulness of past NASN air quality data. The
temperature sensitivity of the SO West-Gaeke method has cast
doubt on the validity and accuracy of past air quality informa-
tion; although we believe that the National trends portray a
reasonable picture of ambient air quality changes that have
occurred.
Similarly, the inaccuracies in the NO2 Jacobs-Hochheiser
(J-H) method, eliminates the NASN as potential source of
long-term trend data. The NASN was useful, however, by serving
as a means of evaluating other measurement techniques (i.e.,
sodium arsenite, TGS and TEA) to replace the J-H method.
For TSP, the NASN has, and continues to provide a
source for determining ambient trends as well as for the
non-criteria pollutants determined from the hi-vol filter
samples. The retention of NASN hi-vol sites are important
for two reasons. First, the NASN and in the future National
Air Quality Trend Sites (NAQTS), will serve as the primary
source of filters for analysis of trace materials. By
retaining existing NASN sites as the filter sample source,
we are able to continue trends analysis for trace metals,
non-metal inorganics and BaP/BSO. Further, by maintaining
a filter storage bank, we are able to do retrospective
analysis for additional pollutants which may become of interest
in the future. This will provide a ready means of determining
air quality trends.
Second, TSP data from NASN sites can continue to be
used for long-term trends analysis purposes. In some locations,
the trend data base goes as far back as the 1950's, making
these sites irreplaceable.
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NASN TSP SAMPLING
The NASN TSP hi-vols should be given priority by the
Regions in their review of monitoring networks for purposes
of establishing the National Air Quality Trend Stations (NAQTS)
monitoring network. This means that NASN hi-vol sites should
be reviewed first to determine if they meet the NAQTS selection
criteria; if not, other State and local sites should be
selected for NAQTS. As many of the NASN hi-vol sites should
be retained as possible as either a NAQTS or SLAMS. Those
NASN sites which do not meet NAQTS selection criteria or are
not considered useful for SLAMS monitoring, should be discontinued,
All NASN sites should be formally designated either a
NAQTS or SLAMS (or discontinued) by the end of FY-1978. However,
filters for all existing NASN sites (whether they are designated
as NAQTS or SLAMS) should continue to be submitted through
the end of CY-1978 so that a complete calendar year of
sampling will be obtained enabling the calculation of annual
averages,
OAQPS will continue to support the analysis of hi-vol
filter samples for trace materials. Because of limited
resources for trace material analysis, between 250 and 300
NAQTS sites will be selected by OAQPS for submission of filters.
The selection process will occur after the Region and State
have designated their SLAMS/NAQTS networks. Thus, the designation
of sites for submittal of filters will occur at different
times for different Regions 'but in no case will occur later
than the end of FY-1978.
Beginning in CY-1979, the NASN will have been phased
out, and the subset of the NAQTS network (selected by OAQPS)
will serve as the source of filter samples.
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SELECTION OF NAQTS SITES FOR FILTER SUBMISSION
Any former TSP NASN site designated as a NAQTS site
will be selected for continued submittal of filters. Additional
filters will be requested from other NAQTS (non-NASN) so
that there were at least:
a) two sites in any urbanized area greater than
250,000 population (if the area is currently
meeting the secondary standards only one site
will be selected)
b) one site in any urbanized area greater than
100,000 but less than 250,000 population
One filter should be returned to EMSL out of every
twelve days. (This is equivalent to every other filter
if a one in six day sampling schedule were followed.) The
filters should be sent to EMSL on a quarterly basis no later
than 45 days after the end of the quarter. Figure 1 shows
in diagram form how the site selection process will work.
SUPPLY OF GLASS FIBER FILTERS BY OAQPS
OAQPS will continue to make available a supply of glass
fiber filters for use by State and local agencies in their
TSP hi-vol networks during CY-1978. ORD (EMSL-RTP) is in
the process of procuring 350,000 filters with a scheduled
delivery date anticipated sometime in October, 1977.
Additional specifications have been added to this year's
procurement to eliminate the problems encountered with
the supply currently in use.' (New specifications have been
included for phosphates, brittleness and mass.)
Beginning in CY-1979, OAQPS will supply filters only
for NAQTS sites. Filters will also be supplied to any State
desiring to use them for their SLAMS network as well. In
early 1978, the Regions should inform OAQPS which States
will want a supply of filters for their SLAMS networks
for CY-1979 sampling.
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NASN SQ^/NO^ BUBBLER SAMPLING
The NASN gas bubblers (S02/N02) should not receive
any special treatment by the Regions during their evaluation
of the usefulness of stations in State and local air monitoring
networks for two reasons: a) because of the methodology problems;
and b) the availability of numerous other sites for national
trends assessments. This means that OAQPS will no longer
require the retention of these stations nor continue to require
prior approval for relocation or shutting down of an NO^/SOp
NASN site. When NAQTS or SLAMS stations are designated, the
NASN stations should be considered in the same way as any other
bubbler in the State or local network.
Further, OAQPS, in the future, will be using primarily
the NAQTS data for trends analysis purposes. SAMWG has
recommended that NAQTS stations use continuous instrumentation
to the maximum extent possible. Therefore, it is anticipated
that few NASN stations will be included in the NAQTS network
unless they can be upgraded by being equipped with continuous
instruments.
S02 NASN sites included in the SLAMS network should
be equipped with a temperature controlled bubbler box to
minimize sample loss. These bubbler boxes are generally
available from at least two vendors.
If the Regional Office is still performing the analysis
of bubbler samples, consideration should be given to discon-
tinuing this analysis. The only exception would be in the
situation where the NASN is used as a quality assurance check
on other State or local air monitoring sites.
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