One of the questions I get is how do I select a NO2 monitor? In this post, I will explain the selection process of the NO2 monitor and things you should keep in mind.
What is Nitrogen Dioxide (NO2)?
Nitrogen Dioxide (NO2) is an extremely toxic gas. Concentrations as low as 4ppm can anaesthetise the nose leading to a false sense of security and over-exposure
Sources of NO2
- vehicle exhausts
- Thermal power stations
- pulp mills
- butane heaters
- gas stoves.
NO2 is also produced in industry and used as an inhibitor to prevent the polymerization of acrylates during distillation, a nitrating agent for organic compounds, an oxidizing agent, rocket fuel, flour bleaching agent, and to increase the wet strength of paper.
Properties of Nitrogen Dioxide
Nitrogen dioxide is a yellow-brown gas with a pungent smell from 0.2 ppm, it is non-flammable and non-explosive, and it is a strong oxidizer that can ignite combustion.
Its reactivity with many chemical compounds (chloride compounds, benzene) can produce explosive gaseous mixtures.
Effects of Nitrogen Dioxide on health
Nitrogen Dioxide is irritating to the eyes and respiratory system. It is very toxic by inhalation as well and can cause burns.
What Are Safe Nitrogen Dioxide Gas Levels?
Various government agencies have recommended gas exposure limits, examples can be seen below.
| Agency | Recommendation / Requirement |
| National Institute for Occupational Safety and Health (NIOSH) | NIOSH Recommended Exposure Limit (REL): 1 ppm, 10-minute ceiling |
| Occupational Safety and Health (OSHA) | 5 ppm average over 15 minutes (Permissible Exposure Limit) |
| American Conference of Governmental Industrial Hygienists (ACGIH) | 3 ppm average over 8 hours & 5 ppm as a short-term exposure limit |
What is A NO2 Monitor?
A NO2 monitor is an electronic device that has a Nitrogen Dioxide sensor, the main function of this device is to monitor the level of NO2 in the environment and alarm when the nitrogen dioxide level exceeds the pre-established threshold.
How Does a NO2 Gas Sensor Work?
A nitrogen dioxide gas detector is composed of electronics and a NO2 sensor. The gas sensor converts the detected nitrogen dioxide level to an electronic signal for microprocessor analysis.
After receiving the sensor signal, the unit displays the NO2 concentration. If the measurement exceeds the pre-set NO2 alarm value, the alarms are triggered.
Sensor technologies used to detect Nitrogen Dioxide
Two sensor technologies are used to detect NO2.
NO2 Electrochemical Gas Sensors
The gas reacts with a working electrode, triggering an electrochemical redox reaction. The generated current is proportional to the detected gas level.
Pro
- Small, fast response, & cheap
- Easy to integrate with electronics
- Immediate ON
Cons
- Limited life from 24 to 36 months
- Influenced by temperature and humidity
NO2 Semiconducting Metal Oxide Gas Sensors
Ozone molecules interact with a film of metal oxide material, where surface redox reactions take place. A power-law relationship transpires between the ozone concentration and conductivity of the sensor.
Pros
- Long lifetime, lasting over five years
- Very sensitive
- Low-cost and simple construction
- Robust
Cons
- Cross-sensitivity to oxidizing gases, such as Cl2 and O3
- 10-minute warm-up time
- Influenced by temperature and humidity
Why Do you need a NO2 monitor?
Even if NO2 gas can be detected by its color and smell, only a nitrogen dioxide detector can accurately measure concentrations of this particularly toxic gas. Thus it is recommended to use fixed or portable nitrogen dioxide detection equipment.
How Do I Select a NO2 Monitor?
To select the right NO2 monitor for you, you need to ask yourself a few questions.
Do I need a portable or a fixed solution?
This is the first question to ask yourself if you need a portable gas or fixed gas detector. Portable gas detectors are useful in certain situations and you can take them everywhere you go, while fixed gas detectors are useful to detect a given area where we know there is a permanent danger.
Read here about portable gas detectors.
Read here about fixed gas detectors.
Do I need a standalone or integrated system?
How do you want to use the NO2 Monitor, to be as a stand-alone or a part of your existing fleet, if it is a fleet you need to consider how it is going to be integrated into the existing detectors.
For portable gas detectors, I recommend them to be from the same manufacturer, and for fixed units make sure that they have the same communication protocols, like 4-20 mA, Modbus, etc.
What is my budget and operating cost budget?
When deciding to buy a gas detector you need to consider the budget you have and the operating costs, this includes calibration, maintenance, and training for the technicians.
Do I need advanced functions such as data logging or Bluetooth?
Do you need a basic NO2 monitor or an advanced one with features like data logging or Bluetooth? remember more features, will cost more.
Do I need specific accreditations with the monitor such as a NIST traceability calibration?
Do you need certification such as a NIST traceability calibration, ATEX, UL, CULus, IECEX, INMETRO, etc? before you buy you need to ask the vendor if the detector has those certifications.
Do I require a belt clip for attaching the device to my clothes?
Depending on where you are going to use the detector you may need a belt clip, you need to verify this before you buy one.
Do I need after-sales support, USA headquarters, or fast calibration services?
This is one of the factors that most people ignore, but having support after you buy gas detectors is something you should factor in before deciding to buy gas detectors.
Also, I know some organizations, especially government agencies, it is important for them that the detectors are assembled or manufactured by a US company.
FAQ: NO2 Monitor
What is the best NO2 Fixed gas detector?
The est NO2 monitor is Sensepoint XCD, it has 4-20mA, three relays, and an optional Modbus connection the part number is SPXCDASMNX. You can buy it from any of Honeywell’s distributors.
What is the best Portable NO2 monitor?
The best portable NO2 monitor is BW SOLO. Honeywell BW Solo Nitrogen Dioxide Wireless Gas Detector measures NO2 from 0 to 100 ppm.
How is NO2 monitored?
By using a NO2 sensor with a selective ozone filter, we can get a direct measurement of NO2 without interference from ozone.
The electrochemical gas sensor in the sensor head generates an electrical current in nA, which is proportional to the concentration of gas that comes in contact with the sensor.
What is a safe level of NO2?
EPA set a 1-hour NO2 standard at the level of 100 parts per billion (ppb). EPA also retained the annual average NO2 standard of 53 ppb.
The 1-hour standard will protect public health by limiting people’s exposure to short-term peak concentrations of NO2 – which primarily occur near major roads.
Is NO2 harmful to humans?
Long-term exposure to high levels of nitrogen dioxide can cause chronic lung disease. It may also affect the senses, for example, by reducing a person’s ability to smell an odor.
High levels of nitrogen dioxide are also harmful to vegetation—damaging foliage, decreasing growth, or reducing crop yields.
What happens if you smell NO2?
Nitrogen dioxide is sparingly soluble in water and on inhalation, it diffuses into the lung and slowly hydrolyzes to nitrous and nitric acid which causes pulmonary edema and pneumonitis leading to the inflammation of the bronchioles and pulmonary alveolus resulting from lipid peroxidation and oxidative stress.
Is a Nitrogen Dioxide (NO2) Gas Detector the Same as a Nitric Oxide (NO) Detector?
No, a Nitrogen Dioxide (NO2) Gas Detector is not the same as a Nitric Oxide (NO) Detector. Most of us know nitric oxide gas (NO) as “laughing gas.” Nitric oxide gas is very different from NO2.
NO gas is used for pain relief by dentists and medical personnel to sedate patients undergoing medical procedures.
There are specific NO sensors used for NO detection.
Do NOx Gas Sensors Exist?
There is no such thing as a NOx sensor. NOx is a “lazy” term to describe both NO2 and NO. Therefore, when one uses NOx it means at least NO2 and NO.
Therefore, there is no NOx gas sensor that can detect both with the same single gas-sensing element. Typically, a NOx detector employs both a NO2 and NO gas sensor.
How Do I Select a Nitrogen Dioxide Detector?
To select the best personal protection nitrogen dioxide gas detector, follow this simple guide.
- What is my budget and operating cost budget?
- Do I need advanced functions such as data-logging or Bluetooth?
- Do I need specific accreditations with the monitor such as a NIST traceability calibration?
- Do I require a belt clip for attaching the device to my clothes?
- Do I need after-sales support, USA headquarters, or fast calibration services?