Environmental protection science

How did ozone, which protects the earth, become the primary pollutant?

Ozone is a blue, irritating gas with the chemical formula O3, which is a "brother" to the well-known oxygen (O2).

We all know that ultraviolet radiation from the sun is very lethal to living things. Fortunately, there is an ozone layer 15 to 25 kilometers above the earth's surface. Although it is not too thick, it can absorb a large amount of ultraviolet radiation from the sun and protect organisms on the earth from ultraviolet damage. Therefore, the ozone layer is also known as the earth's "protective layer".

However, unlike the ozone layer high in the sky, because ozone has strong oxidizing properties, ozone near the ground is a harmful gas and can even become a "health killer." Lower concentrations of ozone have a good bactericidal effect, but if the ozone concentration in the air is too high, it can easily cause inflammatory lesions of the upper respiratory tract, causing symptoms such as coughs and headaches, and can also cause irritation to the skin, eyes, and nasal mucosa.

Therefore, it is true to say that ozone is "a Buddha in the sky and a devil on the earth."

Sources of ozone pollution

Ozone pollution is different from the PM10 we are familiar with. It is not a primary pollutant directly emitted by the pollution source, but nitrogen oxides (NOx) emitted into the air. ), volatile organic compounds (VOCs), secondary pollutants produced by complex photochemical reactions in the air.

Let’s take a look at where nitrogen oxides and volatile organic compounds come from:

Combustion gases mainly come from the combustion of fossil fuels, such as coal, oil, and natural gas. etc.; process waste gases emitted in industrial production, such as paints and coatings, ink printing, chemical product manufacturing, etc.; and vehicle exhaust gases generated by transportation, such as cars, ships, non-road mobile machinery (such as excavators, road rollers, forklifts, etc. etc.

The peak period of ozone pollution

The peak period of ozone pollution is generally from May to September, which is in late spring, summer and early autumn. Strong sunshine, few clouds, weak wind, and high temperature provide more convenient conditions for the generation of ozone.

During the day, due to the lower temperatures in the early morning and evening, the solar radiation is weak, the photochemical reactions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) are weak, and the ozone concentration is low; but from noon to 15 hour or so, if the concentration of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the air is higher, the secondary conversion under the influence of sunlight will cause the ozone concentration to become higher and higher.

In fact, ozone pollution will be produced during the process of controlling PM2.5, and the two are related to each other. Because as the concentration of PM2.5 decreases, the transparency of the space improves, and strong radiation and strong ultraviolet rays are conditions that "help" generate ozone.

How to protect yourself from ozone?

Ozone pollution is very deceptive. It often occurs when the wind is sunny and the sky is clear. It is difficult to detect and can even give people the illusion that "the weather is really nice." To prevent ozone pollution, we can start from the following.

1. When outdoor ozone concentration is high, it is best to reduce going out and outdoor activities. Sensitive people need to take precautions when going out and can wear hats, sunglasses and other protective products.

2. When outdoor ozone concentration is high, going out and outdoor activities can be reduced.

3. When the outdoor ozone concentration is high, reduce the number of indoor ventilation times. If possible, turn on indoor air purification equipment.

4. Regular physical exercise should be increased appropriately to improve physical fitness and immunity, which can appropriately reduce the damage of ozone to the upper respiratory tract.

Ozone is very mobile. Pollution generated in one area may not be felt locally, but instead floats to other places to form ozone. The effect of each city's independent efforts to control ozone pollution will not be too obvious, so joint prevention is required. Only through joint control and coordinated control of nitrogen oxide and volatile organic compound emissions can we fundamentally solve the problem of ozone pollution.