# Presentation: 676159

## Kevin A Cavender, EPA-Office of Air Quality, Planning and Standards 

- Precursor Gas Monitoring
- NOy Monitoring Training Overview

## Outline

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

## 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.

## 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.

## Methodology 

**Measurement Principles**
- NO is measured based on its chemiluminescent with O3
**NO + 0****3**** -> NO****2**** + h*****v***
- 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.

## Methodology

**Diagram of a High Sensitivity NO****y**** instrument**

## 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

## Current Work in Progress

- On going testing – Burden’s Creek  RTP, NC
- To date:  Thermo (TEI) 42CY
- One page summaries
- Technical Assistance Document
- Standard Operating Procedures

## Commercially Available NOy Monitors

-             TAPI 200EU/501 NOy	                          TEI 42CY

- EC9841A-NOy

## Testing Results

- Values in Red – Instrument Stated Specifications

| Make/Model | Thermo  42CY NOy |
| --- | --- |
| Averaging Time | 120 seconds |
| Conc. Range | 0-100 ppb |
| Range Verified through Linearity Test? | Yes |
| Initial Calibration Performed? | Yes |
| LDL | 50 ppt |
| Observed | 40 ppt |
| Noise | 25 ppt RMS - 120 sec |
| Observed | 16 ppt |
| Linearity | 1% FS |
| Observed | 1.0024x – 53.26
r2 = 0.999992
 |

## Testing Results (cont.)

- Values in Red – Instrument Stated Specifications

| Make/Model | Thermo  42CY NOy |
| --- | --- |
| Zero Drift | Negligible |
| Observed | 108 ppt (12 hr) |
| Span Drift | 1 % /day |
| Observed | 3.5% (24 hr) |
| Precision | 1% of reading, or 0.2 ppb |
| Observed | 2.2% |
|  Bias Observed | 11% |
| Response/Lag Time | 120 sec (120 sec avg time) |
| Observed | 15 sec |
| Rise Time | 120 sec (120 sec avg time) |
| Observed | 60 sec |
| Fall Time | 120 sec (120 sec avg time) |
| Observed | 90 sec |

## 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.

## 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

## InstallationRemote Converter

**Remote Converter on 10 meter tower**

## InstallationConverter Plumbing

## Instrument OperationInitial 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 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 > 95%.
- Adjust NO2 + NOz reading to amount of NO2 created

## Instrument OperationConverter 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 (> 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

## 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

## Instrument Operation

| Item  | Range  | Comments |
| --- | --- | --- |
| Full Scale Range | 0 to 200 ppb | Suggested Range.  Reduce to 100 ppb if rural site |
| Units | Part per billion (ppb) | Recommended |
| Compressed Gas Cylinder | 10 – 30  ppm | NIST Traceable Protocol #1 cylinder NO
NIST Traceable Protocol #1 cylinder  |
| Calibration Ranges |  |  |
| a.  zero | 0 ppb |  |
| b.  Level I Span | 180 ppb | 90% of scale.  Reduce to 90 ppb if rural site. |
| c.  Mid Point Span | 100 ppb | 50% of scale.  Reduce to 50 ppb if rural site. |
| d.  Precision Level | 40 ppb | 20% of scale.  Reduce to 20 ppb if rural site. |

## 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)

## 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.