Where are photochemical oxidants primarily produced?

Photochemical oxidants are primarily produced in the troposphere, which is the lowest layer of Earth's atmosphere where most weather events occur and where pollutants are concentrated. This region is also where sunlight interacts with various precursor pollutants, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), leading to photochemical reactions that generate oxidants like ozone.

The troposphere is key to this process because it contains the necessary conditions—sunlight and the right mix of atmospheric gases—for these chemical reactions to take place. Photochemical smog, for example, is a direct result of these reactions occurring in the troposphere.

Other layers or components of the Earth, like the stratosphere, lithosphere, and hydrosphere, either do not facilitate or do not actively contribute to the formation of photochemical oxidants in the same way. The stratosphere is positioned above the troposphere and does not play a role in ground-level air quality issues. The lithosphere refers to the Earth's crust and soil, while the hydrosphere encompasses all water bodies, neither of which are involved in the chemical processes that lead to the production of photochemical oxidants.