Atmospheric sulfur cycling in the tropical Pacific marine boundary layer (12°S, 135°W): A comparison of field data and model results: 1. Dimethylsulfide

Abstract

Shipboard measurements of atmospheric and seawater DMS were made at 12°S, 135°W for 6 days during March 1992. The mean seawater DMS concentration during this period was 4.1 ± 0.45 nM (1σ, n = 260) and the mean atmospheric DMS mole fraction was 453 ± 93 pmol mol−1 (1σ, n = 843). Consistent atmospheric diel cycles were observed, with a nighttime maximum and daytime minimum and an amplitude of approximately 85 pmol mol−1. Photochemical box model calculations were made to test the sensitivity of atmospheric DMS concentrations to the following parameters: 1) sea‐to‐air flux, 2) boundary layer height, 3) oxidation rate, and 4) vertical entrainment velocities. The observed relationship between the mean oceanic and atmospheric DMS levels require the use of an air‐sea exchange coefficient which is at the upper limit end of the range of commonly used parameterizations. The amplitude of the diel cycle in atmospheric DMS is significantly larger than that predicted by a photochemical model. This suggests that the sea‐to‐air DMS flux is higher than was previously thought, and the rate of daytime oxidation of DMS is substantially underestimated by current photochemical models of DMS oxidation.

DMS atmospheric concentrations and sulphate aerosol indirect radiative forcing: a sensitivity study to the DMS source representation and oxidation

“…They state that 3 pptv of BrO prescribed during daytime could resolve the discrepancy. Similar problems with too strong measured diurnal variation of DMS compared to model calculations with standard chemistry were also found by Yvon et al (1996). Box model calculations based on recent kinetic data emphasize the possible strong effects of BrO on DMS and DMSO concentrations (Ingham et al, 1999).…”

Sulfur dioxide in the tropical marine boundary layer: dry deposition and heterogeneous oxidation observed during the Pacific Atmospheric Sulfur Experiment

“…The flux and mean SO 2 observations from the lowest legs (<50 m, n=61) of PASE result in an average v dep just under 0.4 cm s −1 for 10 m winds ranging from 4.5 to 10 ms −1 . Standard modeling approaches tend to assign somewhat larger v dep over the ocean between 0.5 and 1.1 cm s −1 (Langner and Rodhe 1991;Pham et al 1995;Yvon et al 1996;Karl et al 2007). …”

“…Yet even a clear correlation with the primary oxidation product, SO 2 , has been observed only intermittently. The early studies of Bandy et al (1992), Huebert et al (1993), and Yvon et al (1996) in the marine boundary layer (MBL) found minimal relationship between the two species on diurnal time scales, leading to considerable confusion about the source of SO 2 and non-sea salt (NSS) sulfate in remote maritime regions. Seasonal and day-to-day variations observed at Amsterdam Island in the Southern Indian Ocean did exhibit some positive correlations (Putaud et al 1992) confirming the suspicion that SO 2 , with an expected lifetime of only a couple of days, should be linked to DMS far from anthropogenic, or volcanic, sources.…”

A mass‐balance/photochemical assessment of DMS sea‐to‐air flux as inferred from NASA GTE PEM‐West A and B observations

“…[Stull, 1988]. Elevated values of"h" have primarily been used to deal with the problem of how to evaluate the flux associated with DMS that has mixed into the BuL or even the lower free troposphere [Yvon et al, 1996]. The BuL is a zone in the lower troposphere that Russell et al [1998] have recently described as defining a region of intermittent turbulence.…”