Global Atmospheric Budget of Acetone: Air‐Sea Exchange and the Contribution to Hydroxyl Radicals

Abstract

Acetone is one of the most abundant oxygenated volatile organic compounds (VOCs) in the atmosphere. The oceans impose a strong control on atmospheric acetone, yet the oceanic fluxes of acetone remain poorly constrained. In this work, the global budget of acetone is evaluated using two global models: CAM‐chem and GEOS‐Chem. CAM‐chem uses an online air‐sea exchange framework to calculate the bidirectional oceanic acetone fluxes, which is coupled to a data‐oriented machine‐learning approach. The machine‐learning algorithm is trained using a global suite of seawater acetone measurements. GEOS‐Chem uses a fixed surface seawater concentration of acetone to calculate the oceanic fluxes. Both model simulations are compared to airborne observations from a recent global‐scale, multiseasonal campaign, the NASA Atmospheric Tomography Mission (ATom). We find that both CAM‐chem and GEOS‐Chem capture the measured acetone vertical distributions in the remote atmosphere reasonably well. The combined observational and modeling analysis suggests that (i) the ocean strongly regulates the atmospheric budget of acetone. The tropical and subtropical oceans are mostly a net source of acetone, while the high‐latitude oceans are a net sink. (ii) CMIP6 anthropogenic emission inventory may underestimate acetone and/or its precursors in the Northern Hemisphere. (iii) The MEGAN biogenic emissions model may overestimate acetone and/or its precursors, and/or the biogenic oxidation mechanisms may overestimate the acetone yields. (iv) The models consistently overestimate acetone in the upper troposphere‐lower stratosphere over the Southern Ocean in austral winter. (v) Acetone contributes up to 30–40% of hydroxyl radical production in the tropical upper troposphere/lower stratosphere.

Air–sea exchange of acetone, acetaldehyde, DMS and isoprene at a UK coastal site

“…The estimate of Lana et al (2011) is 3 times higher than the PPAO measurements; however that of Wang et al (2020b) is in good agreement. Waterside concentrations of ∼ 7 and ∼ 3 nM were predicted (52 % higher and 43 % lower than the L4 concentration) by Lana et al (2011) and Wang et al (2020b) respectively. The high concentrations in the Lana et al (2011) climatology likely correspond to phytoplankton blooms in the April-May period, which did not occur at the time of our measurements or appear as intensely in the estimations of Wang et al (2020b).…”

“…From the perspective of climatology and global modelling, the NECS was predicted to have an April DMS flux of ∼ 14 µmol m −2 d −1 (Lana et al, 2011) and ∼ 6 µmol m −2 d −1 (Wang et al, 2020b). The estimate of Lana et al (2011) is 3 times higher than the PPAO measurements; however that of Wang et al (2020b) is in good agreement.…”

“…From the perspective of climatology and global modelling, the NECS was predicted to have an April DMS flux of ∼ 14 µmol m −2 d −1 (Lana et al, 2011) and ∼ 6 µmol m −2 d −1 (Wang et al, 2020b). The estimate of Lana et al (2011) is 3 times higher than the PPAO measurements; however that of Wang et al (2020b) is in good agreement. Waterside concentrations of ∼ 7 and ∼ 3 nM were predicted (52 % higher and 43 % lower than the L4 concentration) by Lana et al (2011) and Wang et al (2020b) respectively.…”

“…Waterside concentrations of ∼ 7 and ∼ 3 nM were predicted (52 % higher and 43 % lower than the L4 concentration) by Lana et al (2011) and Wang et al (2020b) respectively. The high concentrations in the Lana et al (2011) climatology likely correspond to phytoplankton blooms in the April-May period, which did not occur at the time of our measurements or appear as intensely in the estimations of Wang et al (2020b). This could be partly related to the interannual variability in plankton dynamics and hence seawater DMS cycling.…”

“…All the models and climatologies discussed here (except for Wang et al, 2020b) used the Nightingale et al (2000 k w parameterisation, which leads to ∼ 26 %, ∼ 14 % and ∼ 26 % higher k w values for acetone, acetaldehyde and DMS, respectively, than those of Yang et al (2011a) over this campaign because of the solubility dependence in bubble-mediated gas exchange (Yang et al, 2011a;Bell et al, 2017). Substituting the Nightingale et al (2000) k w parameterisation with the Yang et al (2011a) k w would generally reduce the flux magnitude in these models, estimated as ∼ 5 %, ∼ 6 % and ∼ 19 % for acetone, acetaldehyde and DMS, respectively (k a unchanged and from COAREG 3.5).…”