Parameterization of OH for efficient computation in chemical tracer models

We present a parameterization for the tropospheric concentration of the hyd roxyl radical (OH) which can be used to overcome the costs of solving kinet ic equations in chemical tracer models. This parameterization accurately re presents OH predicted by a full chemical mechanism. The 24-hour average con centration of OH is represented as a set of high-order polynomials in varia bles such as temperature, latitude, declination, and the concentrations of ozone, water vapor, carbon monoxide, nitrogen oxides (as a family), and hyd rocarbons. The parameterization of OH consists of computer-written FORTRAN functions for an efficient computation of the polynomials. The parameteriza tion of OH is publicly available.