Environmental Science | How much do you know about the basic knowledge of air pollution?

What is air pollution?

Air pollution is caused by various human activities

Air pollution is caused by gases and particles emitted into the atmosphere by various human activities, such as inefficient burning of fuels, agriculture and farming. There are also some natural factors that cause air pollution, including soil dust particles and salt in sea waves.

Air pollutants can be discharged directly from the source (i.e. primary pollutants) or formed by chemical reactions in the atmosphere (i.e. secondary pollutants). When the concentration of these substances in the air reaches a critical level, they will endanger people, animals, plants and ecosystems, reduce visibility, and corrode materials, buildings and cultural sites.

Is air pollution a new problem?

Air pollution has existed for thousands of years

Air pollution is closely related to human beings. It has existed for thousands of years since fire was used for cooking and heating. During the industrial revolution, dangerous high level outdoor air pollution became a problem, and the massive use of coal caused many serious urban air pollution incidents.

The smog incident in London in 1952 is a case in point. In that year, due to the interaction between residents' coal burning, coal for power generation, dirty fuel for transportation and industrial pollution and weather phenomena, pollution shrouded over London, and more than 12000 people died in these days. In response to strong public protests, Britain passed the Clean Air Act (1956).

Where does air pollution come from?

Mostly caused by human activities

Air pollution comes from a wide range of sources, both natural and man-made. Natural sources include volcanic eruptions, waves, soil dust, natural vegetation fires and lightning. Some of the most common anthropogenic sources include power generation, transportation, industry, residential heating and cooking, agriculture, solvent use, oil and gas production, waste burning and building construction. Some sources, such as forest and savanna fires, and windblown mineral dust, occur naturally, but are exacerbated by human activities.

Different pollutants have different sources. In cities, air pollution comes from both inside and outside the city, some from far away places. The main urban pollution sources include vehicles, natural gas, coal and charcoal burning, cooking and heating wood, and industrial sources still located in the city. Many large industrial sources, such as cement plants, steel plants and power plants, are far away from cities. However, since pollutants can spread to far places with the air, urban air pollution is still aggravated. The pollutants emitted by the oil and gas industry and the maritime sector can also spread far away.

Agricultural sources, including burning forests for cultivation and forest fires, have increased air pollution in urban and rural areas. In very dry areas, near deserts and eroded lands, dust blown by wind accounts for a large part of PM2.5. Most ammonia is discharged from agricultural and human waste treatment.

Will air pollution spread?

Air pollution can spread

Air pollution has a significant impact on the places near its source, but since it can spread to far places in the atmosphere, the air pollution generated in one place can also affect far places. For example, pollutants that form fine particles (PM2.5) and ozone (O3) may spread hundreds or thousands of kilometers, thus affecting the entire region and continent.

Although remote air pollutants are one of the causes of local air pollution, nearby pollution sources are still a very important determinant of local air quality. The concentration levels of pollutants such as nitrogen dioxide (NO2) and sulfur dioxide (SO2) are higher near their sources (transportation, energy production and industry). In a city, the pollutant concentration in the area closest to the large pollution source may be higher, while other areas in the same city may be much cleaner.

Atmospheric conditions (such as wind) will affect the diffusion of pollutants and vary greatly. Strong winds make long-distance transmission possible, while a calm environment will lead to the accumulation of pollutants. In large cities in subtropical and tropical regions, serious pollution incidents may occur due to low wind and long sunshine hours. Local weather conditions such as mountains, land and sea breeze around the city will affect the diffusion of pollutants and the formation of secondary pollutants.

Will air pollution cause other environmental deterioration?

Acid rain is a typical case

Some air pollutants will lead to "acid rain". In the 1980s and 1990s, acid rain received special attention in Europe and North America. Sulfur dioxide (SO2) and nitrogen oxides (NOx) react with water in the atmosphere to produce sulfuric acid and nitric acid, which return to the earth in the form of "acid rain".

Acid rain affects the environment by destroying the leaves of plants, thereby reducing the productivity of plants and making the soil lose the nutrients that plants rely on for survival. Acidification of soil and river water kills fish and insects and affects other species that feed on them. Acid rain can also damage buildings and historic sites.

What is the relationship between air pollution and climate change?

Major air pollutants will affect the climate

Air pollution and climate change are intrinsically linked. All major air pollutants will have an impact on climate, and most of them have common sources with greenhouse gases (GHG), especially related to the burning of fossil fuels. They also exacerbate each other's influence in many ways. For example, greenhouse gases such as methane contribute to the formation of ground ozone, and the level of ground ozone will increase with the increase of temperature. Rising temperatures increase the frequency of wildfires, which in turn further increases the level of particulate air pollution.

The pollutants of "short-term climate pollutants" (SLCP) such as black carbon, ozone, methane and hydrofluorocarbons (HFCs) are powerful climate forcing factors and dangerous air pollutants (in terms of ozone and black carbon). Many measures to reduce short-term climate pollutants will also reduce other air pollutants, such as nitrogen oxides. For example, measures to reduce black carbon will affect regional climate change and slow down the rate of recent global warming. They also greatly reduce the emission of pollutants that will lead to PM2.5, thereby benefiting human health. Methane is a powerful greenhouse gas, which forms ozone in the atmosphere. The action to reduce methane is of great benefit to preventing climate change, protecting human health and crop production.