* Oxygen (O2): While oxygen is essential for life, it is highly reactive. It readily combines with other elements and compounds, leading to processes like combustion, rusting, and oxidation.

* Ozone (O3): A highly reactive form of oxygen, ozone is a key component of the stratosphere, where it absorbs harmful ultraviolet radiation. However, it is also a pollutant in the troposphere, causing respiratory problems and damaging crops.

* Nitrogen oxides (NOx): These gases, including nitric oxide (NO) and nitrogen dioxide (NO2), are produced by combustion processes and contribute to smog formation, acid rain, and respiratory problems.

* Sulfur dioxide (SO2): A major air pollutant, sulfur dioxide is released from burning fossil fuels and volcanic eruptions. It reacts with water to form sulfuric acid, a component of acid rain.

* Carbon monoxide (CO): While not as reactive as other gases on this list, carbon monoxide is a colorless, odorless gas that can be lethal in high concentrations. It binds to hemoglobin in red blood cells, preventing the transport of oxygen to the body's tissues.

Other gases in the atmosphere, like nitrogen (N2) and argon (Ar), are generally unreactive. They make up the majority of the atmosphere but do not readily participate in chemical reactions.