Case Study

Investigating Wintertime Haze in Beijing

Researchers used the 2B Tech Model 405 nm NO2/NO/NOx Monitor and the Model 106-L Ozone Monitor to look at the chemistry of a widespread heavy-haze event in Beijing that lasted several days. The measurements were conducted using a moving cabin on a tower platform.

Researchers from Peking University and the China National Monitoring Centre Study the Production of Particulate Nitrate (pNO3) at Ground Level and Aloft The Problem:  Wintertime haze in Beijing can often reach severe levels that can affect human health and visibility in the city. Airborne particles less than 2.5 microns in diameter (PM2.5) are the main cause of hazy conditions in the atmosphere.  Particulate nitrate (pNO3) can account for anywhere between 15% to 40% of the PM2.5 mass concentration in China. The two pathways for generating pNO3in the atmosphere involve the reaction of OH with NO2 in the summertime, and hydrolysis of N2O5 (N2O5 + H2O ⇆ 2HNO3) at nighttime and during the winter. The role of the hydrolysis of N2O5 pathway in the winter is not well understood, but prior modeling and field research has shown that it plays an important role in the atmosphere.

The Solution: Researchers Haichao Wang, Keding Lu, and colleagues at Peking University and the China National Monitoring Centre conducted a study in December 2016 to look at the chemistry and meteorology both at ground level and in the atmosphere during a widespread heavy-haze episode that lasted for several days.

The measurements were conducted using a moving cabin on a tower platform. The Model 405 nm NO2/NO/NOX Monitor and Model 106-L Ozone Monitor were used to make vertical measurements from ground level up to 250 meters.

Results: The researchers found the nighttime atmosphere is chemically quiet near the ground because ozone is reacted away by nitric oxide (NO) emissions. Additionally, N2O5 does not accumulate at ground level because its precursors are reacted away by the NO and VOCs (volatile organic compounds) emitted by surface sources such as power plants, vehicles and industry.

However above 150 meters, a reactive layer above Beijing was identified where pNO3can be produced rapidly at night utilizing the N2O5 hydrolysis pathway. Simulations have shown downward mixing can bring over half of this pNO3to the surface—causing much of the haze in Beijing during the winter!

Click here to access the full research paper:

The 2B Tech Instrument’s Role: The Model 405 nm performed the NO measurements conducted at nighttime during the study. The portability and low power consumption of the Model 405 nm made the instrument the only possible solution to measure NO at ground level and up to 250 meters using the moving cabin and tower platform. The high precision and accuracy of the Model 405 provided the researchers with the information necessary to reach their conclusions about the cause of wintertime haze in Beijing.

The Bottom Line:  The Model 405 nm is the only NOx monitor on the market capable of providing highly accurate NO and NO2 readings with low enough power consumption to be used for remote and portable applications. The instrument provides FEM-approved  direct NO2 readings simultaneously with NO measurements and can be used for any compliance monitoring application. Please reach out to 2B Technologies to discuss using the Model 405 nm for your application.

Related Products

Have questions?

Our flexible systems are compatible with just about any air quality problem. No matter the project, we’ll help you build out the perfect solution.

Related Case Studies

This research investigated how the wavelengths of light emitted by mercury lamps affects radical generation and chemistry in an oxidation flow reactor. Different types of lamps were designed and tested, and the Model 106-M Ozone Monitor measured the ozone concentration at the exit of the flow reactor. Empirical estimation equations could be used to predict the hydroxyl radical production, a much simpler approach than using photochemical models.

In this study, a new method of cleaning the cabins of passenger airplanes was studied. High ozone was pumped into the aircraft’s air conditioning system. The 0-100 ppm range of the Model 106-L enabled researchers to monitor the fumigation levels of the ozone as well as the fallback to safe levels. Hospital-grade sterilization was achieved in about 90 minutes of treatment, with the added benefit of the ability of ozone to penetrate the hard-to-reach places on the plane, such as tray tables in the locked & upright position.

Researchers at the University of São Paulo are studying the use of ozone as a more environmentally sound method for modifying the properties of starch. Industrial sectors that use starch include food, petrochemical, adhesives, paints, and others. This study applied high ozone and used the Model 106-H Ozone Monitor to follow the inlet and outlet concentrations of a reactor containing the starch. The study identified several techniques for optimizing starch properties.