Enviro - NO/NO2 Gas Analyzer

Where do nitrogen oxides (NOx) come from?

Nitrogen oxides mainly refer to nitric oxide (NO) and nitrogen dioxide (NO2), most of which come from the high-temperature combustion process of fossil fuels. Nitric oxide is relatively harmless, but is rapidly oxidized to nitrogen dioxide by ozone in the air. Nitrogen dioxide is also released directly from the burning of nitrogen-containing fuels (such as coal) and nitrogen-containing chemicals. In general, motor vehicle emissions are one of the main sources of urban nitrogen oxides.

Anthropogenic sources of nitrogen oxides (NOx) mainly include automobiles, power plants and factories. In the past, the largest sources of nitrogen oxides (NOx) in the air were thermal power generation, boilers, etc. However, in large cities, the vast majority of nitrogen oxides (NOx) come from vehicle emissions. When the car is running, nitrogen oxides (NOx) are produced in the high-temperature and oxygen-enriched conditions in the combustion process of the internal combustion engine.

• Low detection limit and temperature-drift
• Getting NOX by directly measuring NO and NO2 without NO2-NO converter
• No Interference of particulate matter ,moisture and other factors
• No Optical moving parts ,high reliability, no interference to the measurement by field

Ultraviolet differential optical absorption spectroscopy (DOAS)

Due to the same gas has different absorption in different spectral band, the absorption of different gases in the same spectral band has superposition effect. Through the analysis of continuous spectrum, a variety of gas can be measured at the same time. The holographic grating is used for light splitting of light absorbed by gas to be measured, sensor array are used to convert the spectral optical signals into electrical signals, after obtaining the continuous absorption spectra of medium, and a variety of gas can be measured at the same time.

Unique algorithms of differential optical absorption spectrum

Gas concentration can be obtained by processing the continuous spectrum data. Light beam through the measured gas environment of which the length is L, due to the gas absorption of light, the light energy will decay. Gas absorption of light intensity in wavelengths, can be accurately expressed by Beer – Lambert relation.

In formula:

• Relative intensity of the incident light in wavelength;
• Relative intensity of the emergent light in wavelength;
• Optical path length;
• The concentration of the ith gas;
• The absorption coefficient of the ith gas;
• The extinction coefficient led by particle scattering and other factors.

Ordinary algorithm can’t distinguish whether the light attenuation is caused by the gas absorption or particle scattering, etc. which is not absorption. The differential absorption method is that the gas absorption is decomposed into two parts: ,  is a part of fast change with wavelength.  is a part of slow change with wavelength. Extinction effect that led by the factors such as particle scattering changes slowly with the wavelength. Obviously, the part of the absorption that varies fast with wavelength is only related to gas absorption. Concentration of gas can be obtained by carrying on the corresponding numerical values. Analyzer optical principle is shown in the diagram (Fig. 1-1) below.