The primary component of smoke is:

The primary component of smoke is water vapor. When materials burn, they undergo a combustion process that typically produces various gases and particulate matter, but water vapor is generated from the steam and moisture released during combustion.

While carbon monoxide, particulate matter, and ash are significant components of smoke as well, water vapor constitutes the largest portion of most smoke produced from common combustibles like wood or paper. This is due to the hydrogen content in these materials. The presence of water vapor is a critical aspect when considering smoke's behavior in fire conditions, such as how it rises and disperses. Understanding the predominance of water vapor in smoke can be crucial for fire investigations, atmospheric studies, and fire fighting tactics.