How does nitrogen dioxide primarily occur in a coal mine?

Nitrogen dioxide primarily occurs in a coal mine due to emissions from diesel machinery and explosives. The combustion processes involved in these activities generate nitrogen oxides, including nitrogen dioxide. When diesel engines operate, they burn fuel, producing emissions that release various nitrogen compounds into the atmosphere. Additionally, explosives, when detonated, can create high-temperature environments that also produce nitrogen oxides as a byproduct of combustion. This makes the use of diesel equipment and explosives significant contributors to nitrogen dioxide levels in coal mining environments.

In contrast, dissolution in water is not a primary mechanism for the occurrence of nitrogen dioxide in coal mines; rather, it refers to a different context, such as when gases are absorbed into liquids. Natural gas leakage is also not directly linked to the generation of nitrogen dioxide, as natural gas is primarily methane and does not produce nitrogen oxides through leakage. General atmospheric reactions could generate nitrogen oxides, but the specific context of coal mining primarily points to diesel machinery and the use of explosives as the main sources.