Eddy flux measurements of sulfur dioxide deposition to the sea surface

Abstract

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.

Air/Sea Transfer of Highly Soluble Gases Over Coastal Waters

“…The data show that the gas transfer velocity for SO 2 is less than that for H 2 O, as expected because of diffusive resistance to gas transfer in the interfacial layer just above the sea surface. The Duck field study confirms previous limited field observations at Scripps pier (Porter et al, ). The results are in qualitative agreement with gas transfer theory and bulk parameterizations of gas transfer of highly soluble gases.…”

“…Duck field study confirms previous limited field observations at Scripps pier (Porter et al, 2018). The results are in qualitative agreement with gas transfer theory and bulk parameterizations of gas transfer of highly soluble gases.…”

“…Direct flux measurements of soluble trace gases are challenging, due to low ambient concentrations and high reactivity with inlet tubing and other surfaces. The existing database of eddy covariance air/sea flux measurements for such gases consists of limited studies of acetone (Marandino et al, ; Yang et al, ), methanol (Yang et al, ; ), and SO 2 (Faloona et al, ; Porter et al, ). SO 2 is only moderately soluble but undergoes rapid hydrolysis and ionization in seawater and therefore behaves as a highly soluble gas during air/sea gas transfer (Liss, ; Millero et al, ; Porter et al, ).…”

“…Such studies are needed to explore the processes controlling the air-side resistance to gas transfer and to validate bulk parameterizations. Porter et al (2018) recently reported simultaneous air/sea flux measurements of SO 2 and water vapor from Scripps pier and detected systematic differences in transfer velocities for the two gases. They suggested that such differences could be used to quantify the relative importance of diffusive and turbulent transport and gain insight into the air/sea gas transfer process.…”

Simultaneous detection of ozone and nitrogen dioxide by oxygen anion chemical ionization mass spectrometry: a fast-time-response sensor suitable for eddy covariance measurements

“…For NO 2 (EA 2.27 eV), the normalized sensitivity showed no dependence on O 3 concentrations from 0 to 80 ppbv. Carbonate reagent ion chemistry has been utilized for detection of HNO 3 and H 2 O 2 via adduct formation, raising an additional concern about potential secondary ion chemistry (Reiner et al, 1998). In laboratory calibrations, shown in Fig.…”