What causes the high ozone value in outdoor environment?

High humidity in the air is easy to cause ozone pollution.

Ozone is a strong oxidant with fishy smell. Different from the ozone layer in the stratosphere of the earth's atmosphere, ozone pollution in the lower troposphere is mainly caused by photochemical reactions of volatile organic compounds, nitrogen oxides and other substances in the lower troposphere under strong light, and then photochemical smog dominated by ozone is produced. Generally speaking, ozone pollution will be accompanied by many other oxidants, forming secondary organic aerosol particles, which is also a kind of PM2.5 in essence. Ordinary people may find it difficult to detect ozone pollution, but if you look closely, you can see that there is light blue smoke in the air and feel that the air is spicy and dazzling, indicating that there may be ozone pollution.

Generally speaking, in the summer and autumn with strong sunshine from June to September, the temperature is high (24℃~32℃) and the relative humidity is low, so many places in the city are prone to ozone pollution. Under the irradiation of sunlight, a large number of volatile organic compounds and nitrogen oxides in the air may undergo photochemical reactions, which may cause ozone pollution. The concentration of photochemical oxidants in cities and suburbs is usually higher than that in rural areas, but the concentration of photochemical oxidants in rural areas occasionally increases, sometimes even exceeding that in cities. Of course, this is due to the transmission of the atmosphere, so that the countryside is also "implicated." For example, the Nankou area in Changping, northern Beijing, often reaches the peak of ozone pollution in the afternoon.

The aerosol particles of this photochemical smog are generally in the range of 0.3 ~ 1.0 micron, which belongs to the main pollutant in PM2.5 photochemical smog. The harm of ozone to human health is mainly reflected in the stimulation to human eyes and mucous membranes, as well as the impact on the health of human respiratory system and cardiovascular system. Studies have shown that when the ozone concentration in the air reaches 0.0 1~0.02 mg/L, people can smell it. When it reaches 1 mg/L, it can make people breathe faster and feel chest tightness. 2.5 ~ 5mg/L can cause pulse acceleration, fatigue and headache. Staying 1 hour in this environment will lead to emphysema and even death. Staying in an environment with serious ozone pollution for a long time may also be harmful to skin health and may increase the risk of cancer.

Ozone pollution is mainly gaseous, therefore, wearing a mask can hardly play an effective protective role, and the best way is to take the initiative to protect. The formation of photochemical smog is a cyclical process, which is produced when the sun is strong during the day and disappears after sunset in the evening. Therefore, when the sun is strong within 3 hours in the afternoon, stay away from the roadside with serious decoration pollution and the vicinity of chemical plants. During the active period of photochemical reaction, especially at one or two in the afternoon, try to reduce going out as much as possible; Pregnant women, children and other people have weak resistance to ozone pollution, so try not to go out in the sun; The elderly should try to choose outdoor sports in poor light; In strong light weather, once you feel the air choking and dazzling, try to stay away from it. In addition, a large number of printers, copiers, ozone air purifiers, etc. All of them are used indoors, which may also cause ozone pollution. So this kind of room should be ventilated.