log10OH

Log10OH is a shorthand notation used in chemistry and atmospheric science to denote the base-10 logarithm of the hydroxyl radical concentration, [OH]. The hydroxyl radical is a highly reactive species that drives many oxidation reactions in the atmosphere and in combustion processes. Because [OH] can vary across several orders of magnitude depending on environment, expressing it on a logarithmic scale via log10([OH]) provides a compact, comparable representation.

Notation and units can vary in practice. The mathematical operation is the common logarithm of a positive concentration. In reporting, researchers often either state log10([OH]) directly or use a normalized form such as log10([OH]/[OH]ref) to keep the quantity dimensionless. When using dimensionless forms, care must be taken to interpret the result correctly. A difference of 1 in log10OH corresponds to a tenfold change in the hydroxyl concentration.

Calculation and interpretation: log10OH is computed by taking the base-10 logarithm of the measured or modeled [OH]. Because log scales emphasize relative differences, log10OH is useful for comparing regions or times with very different oxidative capacities. It is commonly employed in data analysis, visualization, and model diagnostics to handle the wide dynamic range of hydroxyl concentrations.

Limitations and considerations: the logarithm is only defined for positive concentrations; zero or near-zero values require small-value flooring or alternative handling. When reporting, it is helpful to accompany log10OH with the corresponding [OH] value to preserve physical interpretation.

See also: hydroxyl radical, log-scale representations in chemistry, atmospheric chemistry.