free radical

1free radicalPrinciple of the detector:

The measurement of HONO concentration in the atmosphere is carried out using wet chemistry method. The basic principle is to use an absorbing liquid and utilize the diffusion between gas and liquid to convert HONO in the sampled gas into nitrite (NO2-), which is then measured using dual channel long path absorption spectroscopy (LOPAP). Long path absorption spectroscopy (LOPAP) is a widely used wet chemical method for measuring the concentration of gaseous nitrous acid in both laboratory research and field observations.

IIfree radicalProduct features of the detector:

a. The classic wet chemistry method has a lower detection rate compared to optical methods, reaching up to 2ppt;

b、 Adopting the dual fiber pool and dual spectrometer measurement principle, one measuring the total sum of HONO and interfering substances, and the other measuring interfering substances, to ensure the accuracy and stability of the measurement results;

c、 Adopting neutral non corrosive solution absorption: Currently, most LOPAP equipment uses a mixture of sulfonamide and hydrochloric acid as the absorption solution, with a pH of around 0, which causes significant damage to the vacuum pump during gas-liquid mixing. In addition, the high acidity of the waste liquid makes it difficult to handle and has an impact on the environment.

d. Automatic degassing system: Effectively removing bubbles in the pipeline is an important factor in the normal operation of the instrument, avoiding interference from bubbles and ensuring the effectiveness of real-time concentration output of the instrument. At present, LOPAP generally does not have a device for removing bubbles, which can be affected by bubbles.

e. Real time concentration output (advantage of calibration system): Currently, there are few LOPAPs on the market that can directly output concentration. Generally, they output the ratio or log value of the reference wavelength to the absorption wavelength intensity, without further processing of the data. We use a specific concentration of nitrite solution or a specific concentration of gaseous nitrous acid (HONO) gas to calibrate the instrument. According to the two-point method, first obtain the zero point, then obtain the response value of a specific concentration, and then invert the corresponding slope value according to Lambert Beer's law. In the software, it is easy to output the corresponding concentration value in real-time by simply outputting the zero point and corresponding slope value.

f. Touch screen control: The gas flow rate, peristaltic pump speed, and light source intensity can be set in real-time using the touch screen. By adjusting the gas-liquid flow rate, it is easy to adjust the measurement concentration range.

g. Liquid level alarm protection system: Add a liquid level alarm system to prevent liquid from being sucked into the flow controller (MFC), vacuum pump, etc., in order to avoid damage to the corresponding components.

h. Timed zero calibration: Through the touch screen, the time and interval for zero calibration can be set, which can effectively check the stability of the instrument and whether the real-time concentration obtained is accurate.

3、 Technical parameters of gaseous nitrous acid (HONO) analyzer:

Range: 5 ppt-2 ppm (expandable);

Detection limit: better than 2 ppt;

Measurement interval: 1-5 minutes (depending on the measurement range);

Calibration method: offline calibration: easily calibrated using nitrous acid standards;

Online calibration method: Automatically generate HONO standard gas and calibrate with standard gas;