That portion of the atmosphere from the surface up to the mixing height. This is the layer of air, usually below a stable layer, within which pollutants are mixed by turbulence and diffusion. Also called mixed layer.
Source:National Wildfire Coordinating Group. 2012. Glossary of Wildland Fire Terminology. PMS 205. Accessed on 9 September 2013. Available at http://www.nwcg.gov