Kevin A Cavender, EPAOffice of Air Quality, Planning and Standards

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

• Methodology
• Current Work in Progress
• Testing Results
• Cautions
• Installation
• Instrument Operation
• Calibration
• Interferences and Operational Issues
• 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 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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Current Work in Progress

• On going testing Burdens Creek RTP, NC
• To date Thermo (TEI) 42CY
• One page summaries
• Technical Assistance Document
• Standard Operating Procedures

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Commercially Available NOy Monitors
TAPI 200EU/501 NOy
TEI 42CY
EC9841A-NOy
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Testing Results
Values in Red Instrument Stated Specifications
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Testing Results (cont.)
Values in Red Instrument Stated Specifications

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Safety Concerns

• Nitrogen oxides are a poisonous gas. Vent any
  nitrogen oxide or calibration span gas to the
  atmosphere rather than into the shelter or other
  sampling area.
• Always use a third ground wire on all
  instruments.
• Always unplug the analyzer when servicing or
  replacing parts.
• If it is mandatory to work inside an monitor
  while it is in operation, use extreme caution to
  avoid contact with high voltages.

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Installation

• Install 10-meter tipping tower near shelter
• Unpack and inspect monitor
• Plumb converter using PFA Teflon
• Mount monitor and converter
• Connect sample and calibration lines (PFA Teflon)
  to bypass pump and monitor
• Connect vacuum pump, ozone dryer column, and
  ozone scrubber column
• Wire thermocouple and converter heater power line
• Turn on and allow 20-30 minutes to warm up
• Check for alarms and out of spec conditions
• Allow 24 hours warm up before calibrating
• Refer to SOP and manual for more detailed
  instructions

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InstallationRemote Converter
Remote Converter on 10 meter tower
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InstallationConverter Plumbing
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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 0
• 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 gt 95.
• 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
• HNO3 not recommended at this time
• 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 Supplied)
• If converter efficiency is less than 90 the
  converter should be repaired/replaced

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Instrument Operation
Item Schedule Multi-point
calibration Initial Zero and span
checks Daily Converter efficiency
tests Weekly Replace ozonator air feed drying
column As needed Inspect and replace sample
filters Weekly Inspect and replace
capillaries Quarterly Digital to analog
converter test As needed Inspect and clean
cooler fins Semi-annually Inspect and clean
fan filters Semi-annually
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Instrument Operation
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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
• Calculate based on ID of tubing, length of
  tubing between converter and analyzer, and total
  flow (bypass flow sample flow)
• Use shorter lines, thick wall tubing, and/or
  higher bypass flow to reduce residence time if
  necessary.
• Ammonia
• Converter may convert a small amount of ammonia
  to NO creating positive NO interference
• Avoid locating near ammonia sources (e.g., feed
  lots)

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Summary

• NOy is a precursor to both ozone and PM2.5.
• OAQPS has tested TEI 42CY against stated
  performance specifications. Will test API
  200EU/501 in coming months.
• Other instrument(s) are available Ecotech
• OAQPS has developed the TAD, SOPs, one pagers to
  support the NCore Level II effort.
• OAQPS is conducting evaluations of alternative
  converter efficiency test compounds. Current
  recommendation is to use n-propyl nitrate.