Why is there less smog in Shenzhen?

A question asked in one sentence can't be answered clearly in one or two sentences:

When burning coal and biomass fuel, particulate matter will be produced, which is referred to as smog particles for short. Among them, PM 10 and PM 2.5 are inhalable particulate matter, and the latter directly enters alveoli.

Haze refers to particles and solids; Fog refers to droplets and liquids, both of which will block the light in the atmosphere and cause air chaos. In the winter arid areas of northern China, in most cases, smog actually refers to haze. It is of great significance to study haze clearly. Using its formation mechanism, smog can be fundamentally prevented.

It is generally believed that the basic source of haze is incomplete combustion. This source is directly related to China's national conditions.

There are 590 million residents in China who use solid fuel to cook directly indoors; 470 million residents directly use solid fuel for indoor heating. Central heating also has a large number of small boilers, and power plants also have a large number of coal-fired boilers. There is an important difference between boilers and ordinary houses in the cause of smog. Low temperature combustion and high temperature combustion will produce different kinds of haze.

One of the original sources of smoke is fire.

Taking wood as an example, the ignition point is about 300 degrees (200-290 degrees). After ignition, it is decomposed into gas and liquid, and then oxidized by oxygen, and the flame temperature doubles. Water accounts for 65,438+05% in dry wood, which plays a very suspicious role in combustion: on the one hand, the dilution of water limits the combustion temperature; At high temperature, water participates in the reaction: H2O+ carbon -H2+ carbon monoxide-carbon +H2O, which occurs repeatedly. The carbon in it is easy to be oxidized, but it is also easy to aggregate under low temperature and hypoxia conditions. Impurities in fuel will accelerate this process. If carbon continues to accumulate, a multi-layer microcrystalline structure can be produced. Collecting such aggregated particles at low temperature is often called carbon black. The gas in the air will not burn nitrogen and other gases, which plays a role in diluting and cooling, which is also the common reason for the limited combustion temperature.

Pure carbon black has a hollow porous structure, and its surface is marked by local oxidation: it has dual characteristics of strong internal adsorption and high surface activity. Carbon black particles continue to adsorb or react with other impurities, and the diameter increases continuously, forming the core of smog particles. Due to the adsorption and protection of porous carbon, harmful substances in the air, such as microorganisms, such as spores, capsid viruses and heavy metal gases, may be adsorbed and protected. Furthermore, particulate matter can form a colloidal structure, which exists stably in the air and threatens people's respiratory system.

Industrial fire

Take the boiler of thermal power plant as an example. Different from ordinary combustion, industrial boilers have been optimized, and the combustion temperature can reach more than 1000 degrees, which greatly improves the thermal efficiency of coal combustion and also brings side effects. Nitrogen in the air reacts with oxygen at high temperature to produce nitrogen oxides, which is a kind of pollution gas. Impurities such as nitrogen oxides and water can produce nitrate and nitrite, which can be used as the core of nitrate-based smog. The sulfur inherent in coal combustion is also oxidized to produce sulfur dioxide, which interacts with nitrogen oxides to produce acidic oxidizing gas, forming a smog core dominated by sulfate. It is worth mentioning that this process is similar to the combustion reaction of automobile engine fuel, and both nitrogen oxides and sulfur dioxide will cause smog. Different from the combustion involved in ordinary houses, industrial boilers and automobile engines have tail gas treatment processes to ensure the recovery of most particles, and the dust removal facilities in thermal power plants can recover more than 99% of particles. But sadly, some irresponsible thermal power plants do not use dust removal facilities, which leads to the serious discharge of particulate matter exceeding the standard.

Influence on people

Once smog is produced, it is difficult to remove it. Unless meteorological conditions permit, smog weather will form an inversion effect in the atmosphere. For example, in the north, the ground is kept low because of smog, and the upper atmosphere is heated by sunlight, forming a stable structure with high density at the bottom and low density at the top. On a normal sunny day, the ground absorbs a lot of heat, and the rising ground air can drive the pollutants on the ground to diffuse upwards, which is interrupted by the inversion effect, resulting in a continuous haze day.

Hazy weather affects people's psychological and physical health, seriously reducing the happiness index. From the pathological point of view, smoke has adverse effects on human respiratory system, cardiovascular system, physiological and reproductive system of pregnant women. Academician Zhong Nanshan's exposition on smog clearly shows that smog has a significant and chronic impact on human body. Statistically speaking, severe smog will increase the phenomenon of premature death.

protect

In the smog environment, the mask that can effectively protect pm2.5 is N95, but it feels stuffy and is not a personal device that can be used for a long time. For the living room and classroom environment, the air purifier can play the role of filtering pm2.5, and one layer of filter screen plays a role. DIY self-made air purifier and commercial purifier all use the same filter screen, which plays the same role. In this respect, it can be expected that air purifiers will have a trend of low prices. The filter device is also used for household vacuum cleaners, which can prevent the leakage of PM0.2-pm 1 particles. In fact, the principle is the same through consumables such as filters.

Individuals should avoid contact with smog as much as possible, and it is useful to wash skin and nasal cavity in time after contact.

Finally, to solve the smog problem, it is necessary to reduce coal consumption, improve the quality of vehicle oil, and use other energy sources such as solar energy, wind energy and biomass energy as much as possible; On the other hand, while reducing the pressure, strictly control the particulate emissions of existing equipment to solve the smog from the source.

The wind direction and energy structure in Shenzhen are the reasons.