A research team led by Prof. XIE Pinhua from Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS), studied the ratio of HCHO and NO2 during a typical pollution episode in Hefei, a city in east central China from Sept. 3rd to 11th, 2020, and found the characteristics of ozone formation control factors.
The research on ozone formation has attracted much attention, but more need to be done to reveal the interaction of ozone and its precursors (NOx and VOCs) from the perspective of three-dimensional space.
In this research, with the help of 2D Multi-Axis differential optical absorption spectroscopy (2D-MAX-DOAS) and LIDAR in detecting spatial information of atmospheric pollutants, scientists performed an experiment of key pollutants and an ozone formation study in Hefei from September 1 to 20, 2020.
"2D-MAX-DOAS is an optical telemetry method," explained RENBo, first author of the paper, "it can retrieve the spatial distribution characteristics of various gaseous pollutants in the atmosphere by collecting solar scattered light at different azimuth and elevation angles."
The most important discovery is that the O3 formation controlling factors changed with altitudes. RENbo further explained the feature of main control factors affected by the tropospheric bottom layer (< 2km) on the formation of ozone.
In the study, it was found that the change of VOCs concentration in the near-surface atmosphere affected the concentration of O3. But the control factors affecting ozone formation in the atmosphere changed into nitrogen oxides (such as NO, NO2) at the height of 400m, then changed into the control of VOCs and nitrogen oxides at the height of 1 km, and finally the factors affecting ozone formation were transformed into VOCs at the height of 1.6km. It can be seen from the observation that when the ratio of HCHO to NO2 concentration in the atmosphere is about 5.50, ozone concentration decreases significantly.
This experiment revealed the spatial characteristics of the main control factors of ozone pollution process.
The characteristics of O3-sensitivity regimes at different heights with time and azimuths (Lines 1 to 4). (Image by REN Bo)
