NO, NO₂ and NO_x Monitoring

Choosing the proper converter will have an effect on performance and operation. Depending on your application, you have two converter options: a stainless steel converter and a molybdenum (also known as "moly") converter. Moly converters are used primarily in ambient applications where the NO₂ concentrations are typically less than 100 ppb. They can be used in source applications when you have low O₂ concentrations of less than 3% and low NO₂ concentrations of less than 1 ppm. Moly converters typically have a life of about 20,000 ppm hours of NO₂.

On the other hand, stainless steel converters are not recommended in ambient applications because they operate at very high temperatures (625° - 635°C) which could break down gases like ammonia, resulting in false readings. Stainless converters are used in almost all source applications except those with very low O₂ levels. When using a stainless steel converter, your sample must have an oxygen concentration of 3% or greater otherwise the oxide layer gets stripped over time and it stops converting NO₂ to NO.

When a green deposit (also known as "green gunk") is noticed in the exhaust line between the ozone destroyer outlet and the pump inlet, it is usually attributed to a copper oxide residue coming from the ozone destroyer. Because the ozone destroyer in a moly converter assembly is filled with a copper mesh material, copper oxide can leach out over time and a greenish color in the tubing will be visible.

Green gunk occurs when the ozone destroyer is not hot enough therefore the recommended solution is to increase the operating temperature of the moly converter. The factory default temperature is 325°C. Try raising the temperature to 335°C – 340°C when troubleshooting a green gunk problem. The converter has a maximum operating temperature of 350°C.

Another way to troubleshoot a green gunk problem is to ensure the ozone destroyer is securely wrapped around the converter, especially if the destroyer was recently replaced. Proper wrapping is necessary for maximum surface contact, optimizing the heat conversion process.

Lastly, ensure fittings extend out of the converter assembly housing. If the ozone destroyer is not placed in the converter assembly properly, the "U” end of the ozone destroyer will stick too far past the end of the converter cartridge, preventing proper heat transfer.

Resolving your green gunk issue is critical to maintaining proper operation and performance. If green gunk gets into the pump head, it deposits on the valves preventing them from operating correctly causing pressure and flow issues. If you still need help getting rid of green gunk, please email or call Technical Support at (866) 282-0430, option 2.

There have been generational changes of the Model 42i Gas Analyzer in which different versions of the pump and capillary have been shipped with the instrument. Successfully identifying your pump and capillary allows for the determination of performance specifications, a proper maintenance schedule and specific spare part order numbers such as a pump rebuild kit. For help in identifying your pump refer to Technical Bulletin TB1111P1 and for a step by step guide in identifying your capillary please refer to TB112911CAP.

Drops in linearity and calibration drift can indicate that it's time to replace the ozone cleanser. For example, if your sample is 12ppm and you are seeing readings of 8ppm followed by a spike to 12ppm, it may be due to a depleted ozone cleanser. Depending on the relative humidity of the instrument air, an ozone cleanser should last one to two years. Keep in mind that the ozone cleanser will last much longer if you are using a permeation dryer.

To replace the ozone cleanser, disconnect the tubing from the top and bottom of the cleanser. Remove the cleanser from the mounting clips and then install the replacement cleanser on the mounting clips. Reattach the Teflon™ tubing to the top and bottom of the ozone cleanser and your instrument is up and running! To order an ozone cleanser, email or call customer service at (866) 282-0430 option 1 and request part number 101016-00.

If you're not currently using a permeation dryer, consider upgrading to achieve more consistent performance and to save on maintenance time. Upgrades can be retrofitted to your existing instrument or can be purchased with new instruments such as the Model 42i Gas Analyzers. To purchase with your new instrument email or call Customer Service at (866) 282-0430 option 1 or to retrofit your existing instrument, contact Technical Support by email or by calling (866) 282-0430, option 2.

Next Month's Topic: Cold weather monitoring