Insights into the role of turbulence on model-measurement agreement of oxidants in forested environments

OH concentrations are a source of much discussed model-measurement disagreement. Under low NOx (NOx := NO + NO2) conditions, like those found in forests and other remote environments, large discrepancies have been noted in model predictions. Reason for this disagreement may, in part, be the lack of accurate representation of turbulence in chemical transport models. Since OH chemistry occurs on a similar timescale to that of turbulent mixing, it is reasonable to assume that inaccuracies in turbulence representations would show themselves in inaccuracies in modelled chemical concentrations. The 0-D or "well-mixed" box model is a common tool used for these model-measurement comparisons, but the well-mixed assumption is problematic in environments like forest canopies where it is frequently used. By using an alternative box modelling scheme that allows for simulated chemical fluctuations arising from turbulence, we can show that realistic deviations from the well-mixed state can have significant consequences on modelled chemistry. To evaluate the effect of heterogeneity of reactants, we can split our concentration into a mean and fluctuating component (ie. [X]=\overline{[X]+[X]'