Kevin A Cavender EPAOffice of Air Quality, Planning and Standards

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Kevin A CavenderEPA-Office of Air Quality,
Planning and Standards
Precursor Gas Monitoring NOy Monitoring Training
Overview
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Outline

• Methodology
• Interferences and operational issues
• Commercially available NOy Monitors
• Calibration
• Current work in progress
• Summary

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Methodology
What is NOy? NOy consists of the sum of all
reactive nitrogen oxides. including NO, and NO2,
and other nitrogen oxides referred to as NOz. NO
NO2 NOz NOy The major components of NOz
include nitrous acids nitric acid (HNO3), and
nitrous acid (HONO), organic nitrates peroxyl
acetyl nitrate (PAN), methyl peroxyl acetyl
nitrate (MPAN), and peroxyl propionyl nitrate,
(PPN), and particulate nitrates.
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Methodology

• Why Measure NOy?
• NOy is a precursor to both ozone and PM2.5
  formation
• Conventional NOx boxes accidentally measure
  some NOz species, but not all.

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Methodology
Measurement Principles NO is measured based on
its chemiluminescent reaction with O3 NO 03 -gt
NO2 hv The amount of light generated is
linearly proportional to the concentration of
NO. NOy is measured by first passing the sample
through a converter that converts NO2 and NOz
species to NO and then measuring for NO as above.
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Methodology
Diagram of a High Sensitivity NOy instrument
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Methodology

• What makes a high sensitivity NOy monitor
  different than a conventional (low sensitivity)
  NOx monitor?
• A high sensitivity NOy monitor is very similar to
  conventional NOx monitors with the following
  exceptions
• Remote converter is located at sample inlet, not
  inside monitor
• Pre-reactor to reduce non-NOy interferences
• Increased sample flow rate
• Reduced reaction chamber temperature and pressure

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InstallationRemote Converter
Remote Converter on 10 meter tower
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Interferences and Operational Issues

• Reaction of NO with ambient O3
• Ambient ozone will react with NO in sample lines
  creating negative NO interference
• Residence in sample line should be kept to less
  than 2 seconds
• Ammonia
• Converter may convert a small amount of ammonia
  to NO creating positive NO interference
• Avoid locating near ammonia sources (e.g., feed
  lots)
• Converter height above ground level and fetch

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Commercially Available NOy Monitors
TAPI 200EU/501 NOy
TEI 42CY
EC9841A-NOy
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Testing Results
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NOy Span Response
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NOy Precision Response
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Histogram of NOy Data Collected at Burden's Creek
Site5/1/05-1/29/06
NO
NOy
NO2 NOz
Percent
0
0-1
1-5
5-10
10-50
50-100
100-200
200
Concentration (ppb)
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Histogram of NOy Data Collected at Burden's Creek
Site5/1/05-1/29/06
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Instrument OperationInitial Calibration

• Note Supply sufficient calibration gas to
  ensure excess flow through converter inlet
  (supply gt 5 liters per minute)
• Supply zero air until stable readings are
  obtained (approximately 20-30 minutes)
• Adjust monitor to read zero response for NO and
  NOy.
• Supply NO calibration gas at approximately 90 of
  scale
• Adjust monitor after stable NO and NOy readings
  are obtained
• Add ozone to calibration gas to produce NO2 at
  approximately 70 of scale
• Amount NO decreases equals the amount of NO2
  created
• Calculate conversion efficiency as (NOy-NO)/(NO2
  created)
• Conversion efficiency should be greater gt 96.
• Adjust NO2 NOz reading to amount of NO2 created

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Instrument OperationConverter Efficiency Test

• Converter efficiency test designed to challenge
  converter with more difficult to convert NOy
  species
• N-propyl nitrate, isopropyl nitrate
• Supply sufficient calibration gas to ensure
  excess flow at converter inlet (gt 5 liters per
  minute)
• Supply calibration gas at approximately 90 of
  scale
• Allow sufficient time for readings to stabilize
• Calculate converter efficiency as
• (NOy reading/Concentration
  Suppliedx100)
• If converter efficiency is less than 96 the
  converter should be repaired/replaced

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Current Work In Progress

• Evaluation of inlet materials for API
• Testing HNO3 loss on stainless steel, silico
  steel, and FTP teflon.
• Evaluation of proof of concept NO/true NO2/NOy
  monitor
• Two converters
• Moly for NOy
• High intensity LED for NO2

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Questions?