Why is there much ozone in ciel phantomhive in spring?

The main reason is that the troposphere changes greatly with the seasonal height, and the spring is abundant, forming ozone.

First of all, the ozone layer refers to the area with relatively high ozone concentration in the stratosphere, and its main function is to absorb short-wave ultraviolet rays (ozone in the ozone layer is mainly produced by ultraviolet rays). In the stratosphere, some oxygen molecules can absorb ultraviolet rays with wavelength less than 240μm in sunlight and decompose to form oxygen atoms. These oxygen atoms combine with oxygen molecules to produce ozone. Spring is close to perihelion, with plenty of sunshine, which is easy to produce ozone, and autumn is close to apohelion, with less sunshine than spring, which is difficult to produce ozone.

Furthermore, the ozone layer is located in the stratosphere, where most of the weather occurs. In spring, there is little rain and relatively abundant sunshine in the northern hemisphere. Continuous rain in autumn will also have a certain impact.