Reconciling observed and predicted tropical rainforest OH concentrations

The average diurnal variation of OH peaked with a midday (10:00-15:00) average of 1.0 x 10(6) (+/- 0.6 x 10(6)) molecules cm(-3). This was substantially lower than previously reported in other tropical forest photochemical environments (2-5 x 10(6) molecules cm(-3)) while the simulated OH reactivity was lower.

The observational data set was used to constrain a box model to examine how well current photochemical reaction mechanisms can simulate observed OH. We used one near-explicit mechanism (MCM v3.3.1) and four condensed mechanisms (i.e., RACM2, MOZART-T1, CB05, CB6r2) to simulate OH. A total of 14 days of analysis shows that all five chemical mechanisms were able to explain the measured OH within instrumental uncertainty of 40% during the campaign in the Amazonian rainforest environment.