Measurements and steady state calculations of OH concentrations at Mauna Loa observatory

In situ OH measurements were made as part of the spring and summer intensives of Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2). These measurements provided an opportunity to compare measured OH concentrations with those predicted by steady state models which use the many other measurements which made up MLOPEX 2 as input parameters. These models thus provide a highly specific real-time view of the environment in which OH was being measured. Both short- and long-term variations of OH are discussed along with their relation to changes in sources and sinks. In general, agreement between measured and modeled OH concentrations is good during periods when free tropospheric air masses, typically downslope, were present. During periods when certain types of upslope boundary layer air dominated the measurement site, however, measured OH concentration averaged about a factor of 2 lower than the model predictions. Possible reasons for the latter differences are suggested, such as unidentified sinks in the boundary layer air.