From Glossary of Meteorology
The ratio of the speeds of a chemical reaction at two temperatures differing by 10°C.
It varies with different materials but is generally near 2 (i.e., the reaction rate doubles for each rise of temperature by 10°C), especially for reactions involving water vapor. This value may be connected with the fact that equilibrium vapor pressure nearly (but not quite) doubles for a rise of temperature by 10°C. The temperature coefficient for bacterial action is also near 2.