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Precursor Gas Monitoring NO y Monitoring Training Overview. Kevin A Cavender EPA-Office of Air Quality, Planning and Standards. Outline. Methodology Interferences and operational issues Commercially available NOy Monitors Calibration Current work in progress Summary. Methodology.

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Kevin a cavender epa office of air quality planning and standards

Precursor Gas Monitoring

NOy Monitoring Training Overview

Kevin A CavenderEPA-Office of Air Quality, Planning and Standards


Outline
Outline

  • Methodology

  • Interferences and operational issues

  • Commercially available NOy Monitors

  • Calibration

  • Current work in progress

  • Summary


Methodology
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.


Methodology1
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.


Methodology2
Methodology

Measurement Principles

NO is measured based on its chemiluminescent reaction with O3

NO + 03 -> 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.


Methodology3
Methodology

Diagram of a High Sensitivity NOy instrument


Methodology4
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


Installation remote converter
InstallationRemote Converter

Remote Converter on 10 meter tower


Interferences and operational issues
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”


Commercially available noy monitors
Commercially Available NOy Monitors

TAPI 200EU/501 NOy TEI 42CY

EC9841A-NOy





Histogram of noy data collected at burden s creek site 5 1 05 1 29 06
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)



Instrument operation initial calibration
Instrument OperationInitial Calibration

  • Note: Supply sufficient calibration gas to ensure excess flow through converter inlet (supply > 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 > 96%.

  • Adjust NO2 + NOz reading to amount of NO2 created


Instrument operation converter efficiency test
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 (> 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


Current work in progress
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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