Abstract
Abstract. Coral reefs have been found to produce the sulfur compound dimethyl sulfide (DMS), a climatically relevant aerosol precursor predominantly associated with phytoplankton. Until recently, the role of coral-reef-derived DMS within the climate system had not been quantified. A study preceding the present work found that DMS produced by corals had negligible long-term climatic forcing at the global–regional scale. However, at sub-daily timescales more typically associated with aerosol and cloud formation, the influence of coral-reef-derived DMS on local aerosol radiative effects remains unquantified. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) has been used in this work to study the role of coral-reef-derived DMS at sub-daily timescales for the first time. WRF-Chem was run to coincide with an October 2016 field campaign over the Great Barrier Reef, Queensland, Australia, against which the model was evaluated. After updating and scaling the DMS surface water climatology, the model reproduced DMS and sulfur concentrations well. The inclusion of coral-reef-derived DMS resulted in no significant change in sulfate aerosol mass or total aerosol number. Subsequently, no direct or indirect aerosol effects were detected. The results suggest that the co-location of the Great Barrier Reef with significant anthropogenic aerosol sources along the Queensland coast prevents coral-reef-derived aerosol from having a modulating influence on local aerosol burdens in the current climate.
Highlights
Dimethyl sulfide (DMS) is an important precursor gas for aerosol formation
It was found that simulations using L11 overestimated DMS surface water concentration (DMSw) in comparison to observations taken during the R2R campaign
While the L11 climatology is, as of writing, the most up-to-date gridded data set of DMSw available, we can see that for this region it significantly overestimates DMS
Summary
Dimethyl sulfide (DMS) is an important precursor gas for aerosol formation. DMS is produced predominantly by marine organisms such as algae and phytoplankton. Oxidation of DMS produces methanesulfonic acid (MSA), dimethyl sulfoxide (DMSO) and SO2, which oxidise further into H2SO4. H2SO4 can subsequently condense onto pre-existing particles, or, if in sufficiently high atmospheric concentration and in the absence of pre-existing surfaces, H2SO4 can nucleate into new particles. Cooler temperatures, higher supersaturation and fewer pre-existing particles can provide ideal conditions for aerosol precursor gases to undergo new particle formation. Merikanto et al (2009) estimate in the marine boundary layer that only 10 % of lowlevel cloud CCN (cloud condensation nuclei) are created by boundary layer nucleation, compared to 45 % in the free troposphere and subsequently entrained to lower levels In the boundary layer the specific conditions needed for new particle formation occur far less frequently. Merikanto et al (2009) estimate in the marine boundary layer that only 10 % of lowlevel cloud CCN (cloud condensation nuclei) are created by boundary layer nucleation, compared to 45 % in the free troposphere and subsequently entrained to lower levels
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