Constraining the concentration of the hydroxyl radical in a stratocumulus-topped marine boundary layer from sea-to-air eddy covariance flux measurements of dimethylsulfide
Author:
Yang M.,Blomquist B. W.,Huebert B. J.
Abstract
Abstract. The hydroxyl radical (OH) is an important oxidant in the troposphere due to its high reactivity and relative abundance. Measuring the concentration of OH in situ, however, is technically challenging. Here we present a robust yet simple method of estimating an OH-equivalent oxidant concentration ("effective OH") in the marine boundary layer (MBL) from the mass balance of dimethylsulfide (DMS). We use shipboard eddy covariance measurements of the sea-to-air DMS flux from the Vamos Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in October and November of 2008. The persistent stratocumulus cloud-cover off the west coast of South America and the associated strong inversion between MBL and the free troposphere (FT) greatly simplify the dynamics in this region and make our budget estimate possible. From the observed diurnal cycle in DMS concentration, the nighttime entrainment velocity at the inversion is estimated to be 4 mm s−1. We calculate 1.4×106 OH molecules cm−3 from the DMS budget, which represents a ~monthly effective OH concentration and is well within the range of previous estimates. Furthermore, when fitted to the measured intensity of solar flux, the resultant diel variation in OH concentration, together with the DMS surface and entrainment fluxes, enables us to accurately replicate the observed diurnal cycle in DMS (correlation coefficient exceeding 0.9). The nitrate radical is found to have little contribution to DMS oxidation during VOCALS-REx.
Publisher
Copernicus GmbH
Reference41 articles.
1. Bandy, A. R., Thornton, D. C., Blomquist, B. W., Chen, S., Wade, T. P., Ianni, J. C., Mitchell, G. M., and Nadler, W.: Chemistry of dimethylsulfide in the equatorial Pacific atmosphere, Geophys. Res. Lett., 23(7), 741–744, 1996. 2. Bandy, A. R., Thornton, D. C., Tu, F. H., Blomquist, B. W., Nadler, W., Mitchell, G. M., and Lenchow, D. H.: Determination of the vertical flux of dimethylsulfide by eddy correlation and atmospheric pressure ionization mass spectrometry (APIMS), J. Geophys. Res., 107(D24), 4743, https://doi.org/10.1029/2002JD002472, 2002. 3. Bates, T. S., Quinn, P. K., Covert, D. S., Coffman, D. J., Johnson, J. E., and Wiedensohler, A.: Aerosol physical properties and processes in the lower marine boundary layer: A comparison of shipboard sub-micron data from ACE-1 and ACE-2, Tellus, Ser. B, 52, 258–272, 2000. 4. Blomquist, B., Fairall, C. W., Huebert, B., Kieber D., and Westby, G.: DMS sea-air transfer velocity: Direct measurements by eddy covariance and parameterization based on the NOAA/COARE gas transfer model, Geophys. Res. Lett., 33(7), L07601, https://doi.org/10.1029/2006GL025735, 2006. 5. Bretherton, C. S. and Pincus, R.: Cloudiness and marine boundary layer dynamics in the ASTEX Lagrangian experiments. Part I: Synoptic setting and vertical structure, J. Atmos. Sci., $52$, 2707–2723, 1995.
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