Abstract. Deposition to the sea surface is a major atmospheric loss pathway for many
important trace gases, such as sulfur dioxide (SO2). The air–sea transfer
of SO2 is controlled entirely on the atmospheric side of the air–sea
interface due to high effective solubility and other physical–chemical
properties. There have been few direct field measurements of such fluxes due
to the challenges associated with making fast-response measurements of highly
soluble trace gases at very low ambient levels. In this study, we report
direct eddy covariance air–sea flux measurements of SO2, sensible heat,
water vapor, and momentum. The measurements were made over shallow coastal
waters from the Scripps Pier, La Jolla, CA, using negative ion chemical
ionization mass spectrometry as the SO2 sensor. The observed transfer
velocities for SO2, sensible heat, water vapor, and momentum and their
wind speed dependences indicate that SO2 fluxes can be reliably measured
using this approach. As expected, the transfer velocities for SO2,
sensible heat, and water vapor are lower than that for momentum,
demonstrating the contribution of molecular diffusion to the overall air-side
resistance to gas transfer. Furthermore, transfer velocities of SO2 were
lower than those of sensible heat and water vapor when observed
simultaneously. This result is attributed to diffusive resistance in the
interfacial layer of the air–sea interface.
Eddy flux measurements of sulfur dioxide deposition to the sea surface