Shanghai's most sensitive monitor: instantaneous monitoring of radioactive elements

According to the "Oriental Morning Post" report, there is a monitoring instrument at the Department of Environmental and Scientific Engineering of Fudan University. Its scientific name is "ATOFMS," a single-particle aerosol time-of-flight mass spectrometer (ATOFMS). Through it, radioactive elements can be quickly and immediately analyzed. The radioactive pollutants generated by nuclear leakage can be monitored in real time. This world-class advanced instrument currently has only 3 sets in China, one in Shanghai.

According to Professor Chen Jianmin, an atmospheric environment expert and deputy director of the Department of Environmental and Science Engineering at Fudan University, the instrument was introduced from the United States in Fudan University in 2006. The sensitivity of heavy metal monitoring is quite high. From the earthquake in Japan to the present, the instrument was introduced. In the 24-hour monitoring, no abnormal data of radioactive elements were detected. All data were as normal as before the earthquake, indicating that Shanghai has not been contaminated by radioactive substances and citizens do not have to worry and panic.

Fu Hong, lecturer of the Department of Environmental and Science Engineering at Fudan University, is responsible for the day-to-day operation management and monitoring of aerosol mass spectrometers. He said that some high-power samplers need to collect a lot of particles in order to monitor different aerosol mass spectrometers, even if only one Particles can also be monitored, and 20 particles can be monitored in one minute. The radioactive metal elements produced by nuclear leakage can be monitored instantaneously.

According to Chen Hong, atmospheric aerosols are composed of particles dispersed in the air. The particle size of these particles is very different from the chemical composition. The traditional aerosol sampling method is to collect aerosol particles on the filter membrane. The resulting chemical composition is therefore the average result of all the particles. However, obtaining information on a single particle is crucial for studying aerosols. The particle size and chemical composition of a single particle can often be used to analyze the source of the particle and its evolution in the atmosphere.

ATOFMS was developed to meet this need. ATOFMS can simultaneously monitor the aerodynamic diameter and chemical composition of single aerosol particles. It consists of three parts: the particle sampling area; the particle size monitoring area; and the time-of-flight mass spectrometry area (mass spectrometry analysis section).

The process of ATOFMS monitoring of the chemical composition of the particles is as follows: When the particles pass through two 532 nm lasers, the particle velocity can be calculated, and the moment when the particles enter the time-of-flight mass spectrometer tube is obtained. After the particles reach the time-of-flight mass spectrometer tube, a strong ultraviolet laser (266 nm) emits and hits the particles. The energy of the laser is absorbed by the particles and the chemical composition of the particles evaporates and forms ions (such as NaCl to form Na and Cl-). The ion mass-to-charge ratio and the amount of ions can then be monitored by time-of-flight mass spectrometry.

It is understood that the sampling site of ATOFMS is located in the Department of Environmental Sciences of Fudan University in Shanghai. This location is close to residential areas and urban arterial roads and can represent a typical urban environment. Atmospheric particles enter ATOFS through a 4m long copper tube (1cm diameter). An air pump (flow rate of about 10 l/min) is attached to the bottom of the copper tube to reduce the residence time of the gas in the copper tube. The entrance to the copper pipe is approximately 5m above the ground.