It would be a homogeneous mixture in small volumes of space, perhaps as much as a cubic kilometre over an open desert area, say. In larger volumes or near inhabited or forested areas it would be a heterogeneous mixture owing to variations in carbon dioxide content.
Heterogeneous mixture.
Heterogenous
heterogeneous
Homogeneous mixture
Milk is a homogeneous mixture.
Homogeneous mixture
Homogeneous mixture
homogeneous mixture
Chocolate milk is a heterogeneous mixture.
It is an element.
it's a compound
Aluminum is an element.