Calibration gas solutions for measuring nitrogen dioxide

Nitrogen dioxide (NO₂) is one of a group of highly reactive gases known as oxides of nitrogen or nitrogen oxides (NO_x). Other nitrogen oxides include nitrous acid and nitric acid. NO₂ is used as the indicator for the larger group of nitrogen oxides.

The major cause of NO₂ in the air is a result of incomplete combustion of fossil fuels with the highest concentrations resulting from diesel vehicles. Coal mining, buses and other diesel vehicles create the greatest hazard for ambient air exposure in mines, tunnels, and enclosed spaces such as repair garages. Also, NO₂ along with nitric oxide, carbon dioxide and sulphur dioxide are all pollutants from power generation.

The main applications for calibration of NO₂ instruments are for personal exposure gas monitoring, fixed area monitoring, emissions (EPA, CEMS) monitoring and exhaust gas measurement.

As the TWA and STEL values are so low, the requirement for nitrogen dioxide calibration gas for personal exposure gas monitoring has typically been either 5ppm or 10ppm. Nitrogen dioxide has been a challenging gas for many users of gas detection instruments as the highly reactive gas has an extremely short shelf life in smaller non-refillable cylinders (7 months). This creates issues with having the gas readily available for immediate requirements.

Smaller cylinders of 34L, 60L or 112L have been the norm for this application primarily because of the short shelf life. In most cases, customers ask for the smallest cylinder because of the shelf life.

Fortunately, CAC GAS & Instrumentation has two solutions available today which can assist in solving this issue.

Electronic gas generators provide gas concentrations of NO₂ down to as low .05ppm to 5ppm. Gas generators use an electrochemical cell which is long lasting. The same base unit can be used with other gas cells (CL2, CL02, HCN, H2S), providing flexibility for measuring other gases. Although an initial capital cost is required, they are very cost effective over time and provide a long-term solution. The electrochemical cell can be stored when not in use providing customers with NO2 gas when they need it, even for very infrequent requirements.

The 36-month shelf life “white top” specialty gas mixture cylinder is an excellent solution for those customers with multiple instruments. High pressure cylinders are available in larger capacities of 900 and 4000 litres of gas. These cylinders are specifically treated and conditioned to provide stability over this extended shelf life. Based upon using only two litres of gas per monthly calibration, a customer would only need to have 10 instruments to consume 900 litres within the shelf life. That does not include bump testing/response testing which should be done daily.    

These cylinders are also available for our EPA and CEMS standards providing long term environmental monitoring solutions for all NO₂ applications.

As has been demonstrated, there are multiple options for calibrating and bump testing NO₂ instruments and sensors which can meet customers specific requirements.