Best NOx Analyzer (updated for 2024)

Best NOx Analyzer (updated for 2024)

A NOx gas analyzer is used to monitor NOx emissions from combustion engines found in vehicles and small gasoline engines. A NOx analyzer is an important tool that measures the concentration of nitrogen oxides (NO and NO2) in exhaust gases. By providing accurate data on NOx composition, these analyzers offer valuable insights into engine performance and emissions compliance. This information helps identify potential issues affecting engine operation or adherence to emissions regulations. Implementing NOx analyzers enables proactive maintenance, optimizes engine efficiency, and ensures compliance with environmental standards. Gas detection technology plays a vital role in mitigating the environmental impact of combustion engines and promoting cleaner air quality.



  • Affordable NOx Exhaust Gas Analyzer for detecting nitric oxide (NO) and nitrogen dioxide (NO2)
  • NO + NO2 = NOx
  • Quick and easy test to perform, takes less than 2 minutes.
  • NOx Exhaust Gas Analyzers can help to identify pollutants particularly from diesel vehicles
  • NOx Exhaust Gas Analyzers are very expensive
  • Much confusion to a NOx measurement, which is usually only a NO measurement
  • 5 gas analyzers are very expensive
  • NOx, NO and NO2 are pollutants that must be controlled with regards to emissions

Best NOx Exhaust Gas Analyzers?

The most trusted and best NOx Exhaust Gas Analyzer are the following:

What is a Vehicle NOx Exhaust Gas Analyzer?

A Vehicle NOx Exhaust Gas Analyzer is an instrument that reads the exhaust gases and specifically measures nitric oxide (NO) gas and nitrogen dioxide (NO2) and reports these levels, commonly abbreviated as NOx.


Nearly all analyzers advertised as NOx analyzers are in fact only Nitric Oxide analyzer (NO). Therefore when researching for a NOx analyzer always ask what is exactly being measured? Some instruments only measure NO and then perform calculations to predict NOx.

The NOx analyzer has a probe that is inserted into the exhaust pipe of the vehicle. The probe draws a sample of the exhaust gas, which is then analyzed by the analyzer. The analyzer displays the NOx concentration in parts per million (ppm).

Is a NOx Analyzer a Common Tool?

A vehicle NOx exhaust gas analyzer is not a very common instrument. A more common gas analyzer employed is a vehicle 5 gas analyzer. However, there are instances where a 5-gas analyzer is overkill and only a NOx analyzer is appropriate (and usually more affordable).

What are bad NOx ppm Levels?

NOx vehicle exhaust gas testing is usually performed when the engine is under load. High NOx readings over 100ppm indicates that the engine is running lean. In addition high NOx levels are normally caused by high combustion temperatures and pressures, slightly lean AFR, and excessively advanced ignition timing.

What is NOx Gas?

Nitrogen oxides (NOx) are a group of gases that are formed when fuel is burned at high temperatures. NOx emissions from vehicles can contribute to smog, acid rain, and respiratory problems.

Smog is a type of air pollution that occurs when NOx reacts with other pollutants in the atmosphere. Smog can cause eye irritation, respiratory problems, and other health problems.

Acid rain is a type of environmental pollution that occurs when NOx and other pollutants react with water vapor in the atmosphere. Acid rain can damage trees, crops, and buildings. NOx can also irritate the lungs and make it difficult to breathe. People with asthma and other respiratory problems are especially vulnerable to the effects of NOx.

To reduce NOx emissions from vehicles, governments have implemented emission standards for vehicles. These standards require vehicles to be equipped with emissions control devices that reduce the amount of NOx that is emitted.

NOx Exhaust Gas Analyzer Applications?

NOx exhaust gas analyzers are essential tools for monitoring and controlling nitrogen oxide (NOx) emissions from combustion processes. They are also sometimes called NOx detectors, NOx analyzers, NOx emission analyzers, NOx devices, and NOx monitors. These instruments play a crucial role in a range of industries and applications to ensure compliance with environmental regulations and optimize combustion efficiency.

Automotive emissions testing is a key area where NOx gas analyzers are used. They help in measuring NOx levels in vehicle exhaust gases during manufacturing, maintenance, and inspection processes. Ensuring that vehicles meet emission standards contributes to improved air quality and compliance with environmental regulations.

NOx analyzers are also used for environmental monitoring and air quality assessment. They help measure NOx concentrations in urban areas, as well as in sensitive ecosystems. This data, in turn, aids in understanding air pollution patterns and formulating effective pollution control strategies.

What is the difference between NOx, NO and NO2 Detectors?

  • NOx detectors measure the total concentration of nitrogen oxides (NOx) in the air. NOx is a group of gases that includes nitric oxide (NO) and nitrogen dioxide (NO2). So in other words, the reported concentration of NOx is the summation concentration of all the NOx components. NOx = NO + NO2.
  • NO detectors measure the concentration of nitric oxide (NO) in the air. NO is a colorless gas that is produced when fuel is burned at high temperatures.
  • NO2 detectors measure the concentration of nitrogen dioxide (NO2) in the air. NO2 is a reddish-brown gas that is a major component of smog.

NOx detectors provide a more comprehensive solution by detecting both NO and NO2 gases. This dual-function goal makes them ideal for monitoring overall NOx emission levels from industrial processes, combustion engines, and other sources of nitrogen oxides.

How does a NOx exhaust gas analyzer work?

The operation of a NOx gas analyzer typically involves two main components:

  • a gas sampling system and,
  • a gas detection system.

The gas sampling system collects the exhaust gas sample. This is done with a stainless steel probe, alligator clip (to the exhaust), high temperature tubing, water trap filter to catch any exhaust condensate, and a fine particle filter to trap any exhaust particulate matter that may create gas sample or gas sensor blockage.

The gas detection system includes electrochemical gas sensors. An electrochemical gas sensor works by measuring the change in electrical current that occurs when a gas reacts with a sensor. In the case of the Forensics Detectors NOx exhaust gas Analyzer, a NO electrochemical gas sensor is present and so too is a NO2 electrochemical gas sensor. The amount of current produced is proportional to the concentration of NOx in the sample. The analyzer measures the current and displays the NOx concentration in parts per million (ppm).

What produces NOx Gas?

NOx gases, mainly consisting of nitrogen monoxide (NO) and nitrogen dioxide (NO2), are harmful emissions formed through a variety of human-driven and natural processes. In general, these gases are generated when high temperatures cause nitrogen and oxygen to react together.

One of the most significant sources of NOx gas is the combustion of fossil fuels. This occurs in a wide range of industries and transportation sectors. For instance, vehicles like cars, trucks and buses powered by gasoline or diesel engines produce a large amount of NOx emissions during their operation. Similarly, industrial processes such as power generation in coal or gas-fired power plants, as well as manufacturing industries, contribute to the release of NOx gases.

Another contributor to NOx gas production is agricultural activities, in particular the application of nitrogen-based fertilizers. These fertilizers, when broken down in the soil, can release nitrogen oxides into the atmosphere. Livestock farming practices, especially large-scale operations, also emit significant amounts of NOx gases through the manure management process.

Natural sources of NOx gases include natural biological processes in the soil, volcanic eruptions, and lightning. These sources, however, generally account for a relatively small proportion of total NOx emissions compared to human activities.

What are the allowed NO, NO2 and NOx Levels (ppm)?

Atmospheric NOx levels usually are measured with a parts per billion scale (ppb). As an example 1ppm = 1000 ppb. EPA average NO2 atmospheric NO2 concentration is 53 ppb or 0.053 ppm. This is considered a low NO2 concentration.

In vehicle exhaust gas settings, NOx levels are much higher. Usually NO or NO2 level (summation gives NOx), is between 10 to 1000 ppm.  

There are however regulations for NO, NO2 and NOx. Some enforced levels are included here:

  • American Conference of Governmental Industrial Hygienists (ACGIH) has set a Threshold Limit Value (TLV) for NO of 25 parts per million (ppm) as an 8-hour time-weighted average (TWA).
  • OSHA standards for NO2 exposure includes Permissible Exposure Limit (PEL): 5 ppm as an 8-hour TWA

Effective Operation of NOx Devices

Effective operation of the NOx analyzer has all to do with taking care of it with regards to regular calibration and care of use. This involves cleaning the sensing elements to ensure that they are free from dirt and dust, which can affect the accuracy of the measurements. Calibration should be carried out at least annually, or even between on a 6 month periodic basis.

What is the difference between a NOx Combustion Analyzer and a NOx Exhaust Analyzer?

A NOx Combustion Analyzer and a NOx Exhaust Analyzer are both devices designed to detect and measure the levels of nitrogen oxides (NO and NO2) in gases produced during combustion processes. However, they serve different purposes and are used in varying applications. Also they typically have different probes, one has a probe for easy flue measurements, and the other has a probe for easy vehicle exhaust gas measurements (usually with a clip mount).

A NOx Combustion Analyzer is primarily used for analyzing the efficiency of combustion processes in heating systems like boilers, burners, and furnaces. This type of analyzer measures the concentration of NOx directly in the flue gases inside the combustion chamber. By doing so, it helps to optimize the performance, reduce emissions, and ensure the safety of combustion equipment. NOx Combustion Analyzers are often employed in settings such as industrial plants, public facilities, and residential buildings.

On the other hand, a NOx Exhaust Analyzer is specifically designed to monitor and measure NOx emissions from vehicle exhaust systems. It is used in automotive testing facilities, service centers, and inspection stations to ensure that vehicles comply with emission regulations imposed by governmental agencies. With the growing concern for reducing air pollution, NOx Exhaust Analyzers are essential tools for identifying high-emitting vehicles and helping to bring them into compliance.

How to calibrate a NOx exhaust gas analyzer?

Calibrating a NOx exhaust gas analyzer is essential for ensuring accurate and reliable measurements of nitrogen oxides in the emissions from combustion processes. The calibration process generally involves the following steps:

  1. Prepare calibration gases: Obtain certified calibration gas mixtures with USA NIST traceable gas sources of NO and NO2 concentrations. 

  2. Set up the analyzer: Connect the NOx analyzer to the calibration gas cylinders using appropriate tubing, fittings and flow rate of gas. Make sure the instrument is in a well-ventilated area and that all connections are secure.

  3. Zero calibration: Perform a zero calibration by exposing the analyzer to a NOx-free gas, usually nitrogen or clean fresh air. Adjust the zero setting on the analyzer until it indicates the absence of NOx. This step is crucial for eliminating background signals and ensuring accurate readings.

  4. Span calibration: Introduce the calibration gas with a known NO and NO2 concentration to the analyzer. Allow the instrument to stabilize and then adjust the span setting on the analyzer until the displayed concentration matches the concentration of the calibration gas.

  5. Repeat calibration: To verify the accuracy and stability of the calibration, repeat the zero and span calibration steps using different calibration gas concentrations. This can help identify any potential issues with the instrument or calibration procedure.

It is important to follow the manufacturer's recommendations for calibration frequency and procedures. Some NOx analyzers may have built-in self-calibration features, while others may require manual calibration on a regular basis. 

How much does a NOx exhaust gas analyzer cost?

NOx exhaust gas analyzers cost between $1000 to $5000. 

Mid-range NOx gas analyzers, which offer more features and better performance, can be priced around $5000 to $10,000. These devices often include multiple sensors to measure various gases in addition to NOx, data logging capabilities, and advanced diagnostic features. Some of these analyzers may also be portable, allowing for convenient on-site testing and measurements.

For high-end NOx detectors aimed at parts per billion atmospheric detection which are over $15,000. Most high-end NOx analyzers are designed for continuous emission monitoring, making them suitable for regulatory compliance and long-term emission control in larger facilities.

What is the difference between NOx and SOx?

NOx and SOx are two types of gaseous pollutants emitted through various industrial processes, including combustion in power plants and vehicle engines. SOx refers to sulfur oxides, mainly sulfur dioxide (SO2) and sulfur trioxide (SO3). SOx emissions occur when sulfur-containing compounds in fuels, such as coal and oil, are burned. This process releases SOx gases into the atmosphere.

The environmental impact of both NOx and SOx emissions is significant. NOx can contribute to the formation of ground-level ozone, a primary component of smog. Ozone can cause respiratory problems and other health issues in humans, and it contributes to the deterioration of ecosystem health. Additionally, NOx emissions promote the formation of acid rain and particulate matter, which can negatively affect water quality, soil health, and vegetation. The formation of NOx in combustion processes is sensitive to factors like fuel type, combustion temperature, and other combustion conditions.

SOx gases also contribute to air pollution and acid rain. Their impact on human health includes respiratory problems, particularly among sensitive populations such as children and the elderly. SOx emissions can also harm the environment, as sulfuric acid deposition in the form of acid rain can lead to the acidification of water bodies and soil, as well as damage to buildings and infrastructure. In contrast to NOx, SOx emissions are primarily influenced by the sulfur content in the fuel being burned.

What causes high NOx emissions?

There are a number of factors that can cause high NOx emissions in vehicles. Some of the most common causes include:

  • High combustion temperatures: NOx emissions are more likely to occur when the combustion temperature is high. This can happen when the engine is running lean (not enough fuel) or when the engine is not properly tuned.
  • Lean fuel mixture: A lean fuel mixture means that there is not enough fuel to fully oxidize the air in the combustion chamber. This can also lead to high NOx emissions.
  • Exhaust gas recirculation (EGR) problems: EGR is a system that recirculates some of the exhaust gas back into the engine. This helps to reduce NOx emissions by cooling the combustion chamber and by providing more oxygen for the combustion process. If the EGR system is not working properly, it can lead to high NOx emissions.
  • Catalytic converter problems: The catalytic converter is a device that helps to reduce harmful emissions from vehicles. It does this by converting NOx into harmless nitrogen and oxygen. If the catalytic converter is not working properly, it can lead to high NOx emissions.
  • Engine overheating: Engine overheating can also lead to high NOx emissions. This is because the high temperatures can cause the nitrogen and oxygen in the air to react and form NOx.
  • Defective emission control devices: Vehicles are equipped with emission control devices to reduce harmful emissions. If these devices are defective, they can lead to high NOx emissions.

CASE STUDY: Testing NOx to various vehicle conditions

There are various scenarios where an internal combustion engine is operating and one must interpret the data and various gas levels. Below is the best practical undertaking of real working vehicle exhaust with step by step explanation of various gas levels and what they mean to the engine running.

Can you smell NOx?

While NOx gases are generally colorless, they can have a slight odor depending on their concentration. At high concentrations, NOx gases can produce a smell similar to burning, such as in vehicle exhaust or industrial emissions. However, in general, NOx gases are not easily detectable by smell at lower concentrations, hence why it is important to use a NOx analyzer to obtain quantitative NOx ppm levels. 

What are NOx ppm levels?

NOx gases are reported and measured in the parts per million or parts per billion.

The parts per million (ppm) scale is used to express the concentration of a gas in a gas matrix. It is defined as one part of the gas per million parts of the mixture. 

The ppm scale is a convenient way to express very small concentrations of gases. For example, the concentration of carbon dioxide in the atmosphere is about 410 ppm. 

The ppm scale is also used to express the concentration of other gases in the atmosphere, such as methane, nitrous oxide, and ozone. It is also used to express the concentration of gases in industrial processes, such as the concentration of sulfur dioxide in smokestacks.

The ppm scale is a dimensionless unit, which means that it does not have a specific unit of measurement. However, it is often expressed in units of milligrams per cubic meter (mg/m3) or micrograms per cubic meter (µg/m3).


Gas detection is vital for monitoring NOx emissions from combustion engines, with NOx exhaust gas analyzers playing a crucial role in performance evaluation and emissions compliance. Trusted brands like Forensics Detectors, Bridge Analyzers, Kane, Snap-ON, Nova Analytical, Ansed Diagnostic Solutions, Servomex, and Cambustion offer reliable NOx analyzers that primarily measure nitric oxide (NO) gas. These analyzers are essential for automotive emissions testing and air quality assessment, as NOx, NO, and NO2 are pollutants contributing to smog, acid rain, and respiratory issues. Regular calibration of NOx analyzers is critical for accurate measurements and should be performed diligently to ensure precise data collection and informed decision-making regarding engine performance and environmental impact.

    About The Author

    Dr. Kos Galatsis ("Dr.Koz") is the President of FORENSICS DETECTORS where the company operates from the scenic Palos Verdes Peninsula in Los Angeles, California. He is a subject matter expert on gas sensor technology, gas detectors, gas meters, and gas analyzers. He has been designing, building, manufacturing, and testing toxic gas detection systems for over 20 years.

    gas detector expert

    Every day is a blessing for Dr. Koz. He loves to help customers solve their unique problems. Dr. Koz also loves spending time with his wife and his three children going to the beach, grilling burgers, and enjoying the outdoors.

    Read more about Forensics Detectors.

    Phone: +1 424-341-3886