Natural gas power plants are generally considered to be cleaner sources of energy compared to coal-fired power plants and do not contribute significantly to urban air pollution.

Photochemical smog, a type of air pollution common in urban areas, is primarily composed of ozone (O3), which is formed through chemical reactions involving nitrogen oxides and volatile organic compounds in the presence of sunlight.

China has been consistently ranked as one of the top emitters of greenhouse gases, including carbon dioxide, due to its reliance on coal-fired power plants and rapid industrialization.

Transboundary air pollution refers to the movement of air pollutants across national or regional boundaries, often affecting air quality in neighboring countries or regions.

Sulfur dioxide (SO2) is a major contributor to acid rain, as it reacts with water vapor in the atmosphere to form sulfuric acid, which can then condense and fall to the ground as acid rain.

Deposition refers to the process by which air pollutants are removed from the atmosphere and deposited onto surfaces such as land, water, or vegetation.

Nitrogen oxides (NOx), particularly nitrogen dioxide (NO2), are key contributors to the formation of smog, as they react with sunlight and other pollutants to form ozone and other smog components.

Photolysis refers to the process by which air pollutants undergo chemical reactions when exposed to sunlight or other forms of radiation.

Particulate matter (PM) itself is a major air pollutant, consisting of solid or liquid particles suspended in the air, and is not primarily responsible for its own formation.

Emission refers to the process by which air pollutants are released into the atmosphere from various sources, such as vehicles, industrial activities, and natural processes.

Renewable energy sources, such as solar and wind power, do not directly contribute to air pollution, unlike deforestation, industrialization, and transportation.

Transformation refers to the process by which air pollutants undergo chemical or physical changes in the atmosphere, converting from one form to another.

Sulfur dioxide (SO2) is a major contributor to acid rain, as it reacts with water vapor in the atmosphere to form sulfuric acid, which can then condense and fall to the ground as acid rain.

Deposition refers to the process by which air pollutants are removed from the atmosphere and deposited onto surfaces such as land, water, or vegetation.

Nitrogen oxides (NOx), particularly nitrogen dioxide (NO2), are key contributors to the formation of smog, as they react with sunlight and other pollutants to form ozone and other smog components.