Three‐dimensional radon 222 calculations using assimilated meteorological data and a convective mixing algorithm

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Abstract
The distribution of 222Rn is simulated using a three‐dimensional chemistry and transport model driven by assimilated data. The multiyear calculation is the first to use meteorological data from the Goddard Earth Observing System data assimilation system (GEOS‐1 DAS). In addition, this calculation is the first to use moist convection and boundary layer parameters directly from a DAS to calculate mixing via moist convection and turbulence. Previously, these quantities have been derived after the assimilation procedure. Model output and data are compared at sites selected to evaluate model performance in a range of dynamic environments. Simulated afternoon boundary layer concentrations are within 30% of observed concentrations. Simulated nighttime concentrations are ≈50% of measured values although the bias is greatly reduced (and even disappears at Socorro, New Mexico) when nocturnal sub‐grid‐scale turbulent mixing is suppressed. Continental profiles are “C‐like”; a result that is consistent with the moist convective algorithm's tendency to move material from the planetary boundary layer (PBL) to the upper troposphere directly. CTM‐calculated 222Rn at Bermuda closely matches observations even during periods of frontal passage showing that the atmospheric circulation is accurate and that ventilation of the continental PBL is realistic. Model‐calculated 222Rn concentrations in the marine upper troposphere are consistent with observations in the eastern Pacific and near Darwin.