# Presentation: 838157

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

- Precursor Gas Monitoring
- NOy Monitoring Training Overview

## Outline

- Methodology
- Interferences and operational issues
- Commercially available NOy Monitors
- Calibration
- Current work in progress
- 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 reaction 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

## InstallationRemote Converter

**Remote Converter on 10 meter tower**

## 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

-             TAPI 200EU/501 NOy	                          TEI 42CY

- EC9841A-NOy

## Testing Results

| Make/Model | Thermo  42CY NOy
(observed)
 | API 200EU/501
(observed) |
| --- | --- | --- |
| Averaging Time | 120 seconds | 120 seconds |
| Conc. Range | 0-100 ppb | 0-100 ppb |
| Zero Drift (0.1 ppb/day) | 12 hr.   (0.1 ppb)
24 hr.    (0.1 ppb) | 12 hr.   (0.03 ppb)
24 hr.    (0.05 ppb) |
|  Span Drift | 20% FS  (0.3%)
80% FS  (0.6%) | 20% FS  (0.5%)
80% FS  (1.2%) |
| Precision (Coefficient of Variance) | 1.49% | 2.67% |
|  Bias  | +/-1.19% | +/-2.73% |
| LDL (0.05 ppb)  | 0.05 ppb | 0.05 ppb |
| Noise (0.025 ppb)  | 0.013 ppb | 0.009 ppb |
| Linearity (1% FS.  M, B, and R2 reported) | 1.0003x-0.0753
R2 = 0.9999 | 1.0088x-0.0418
R2 = 0.9999 |
| MDL Observed | 0.050 ppb (0.03 – 0.13 ppb CL) | 0.058 ppb (0.04 – 0.11 ppb CL) |

## NOy Span Response

## NOy Precision Response

## Histogram of NOy Data Collected at Burden's Creek Site5/1/05-1/29/06

- Percent

- 0

- 0-1

- 1-5

- 5-10

- 10-50

- 50-100

- 100-200

- 200+

- Concentration (ppb)

- NO

- NOy

- NO2 +
- NOz

## Histogram of NOy Data Collected at Burden's Creek Site5/1/05-1/29/06

| Bin | NO | NOy | NO2+NOz |
| --- | --- | --- | --- |
| 0 | 728 | 8 | 140 |
| 0-1 | 1958 | 53 | 50 |
| 1-5 | 962 | 1283 | 1452 |
| 5-10 | 240 | 1380 | 1499 |
| 10-50 | 452 | 1482 | 1489 |
| 50-100 | 196 | 275 | 0 |
| 100-200 | 92 | 146 | 0 |
| 200+ | 2 | 3 | 0 |
| Total | 4630 | 4630 | 4630 |

## 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 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 

- 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

- 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

## Questions?