New constraints on terrestrial and oceanic sources of atmospheric methanol

Abstract

Abstract. We use a global 3-D chemical transport model (GEOS-Chem) to interpret new aircraft, surface, and oceanic observations of methanol in terms of the constraints that they place on the atmospheric methanol budget. Recent measurements of methanol concentrations in the ocean mixed layer (OML) imply that in situ biological production must be the main methanol source in the OML, dominating over uptake from the atmosphere. It follows that oceanic emission and uptake must be viewed as independent terms in the atmospheric methanol budget. We deduce that the marine biosphere is a large primary source (85 Tg a −1 ) of methanol to the atmosphere and is also a large sink (101 Tg a −1 ), comparable in magnitude to atmospheric oxidation by OH (88 Tg a −1 ). The resulting atmospheric lifetime of methanol in the model is 4.7 days. Aircraft measurements in the North American boundary layer imply that terrestrial plants are a much weaker source than presently thought, likely reflecting an overestimate of broadleaf tree emissions, and this is also generally consistent with surface measurements. We deduce a terrestrial plant source of 80 Tg a −1 , comparable in magnitude to the ocean source. The aircraft measurements show a strong correlation with CO (R 2 =0.51−0.61) over NorthCorrespondence to: D. B. Millet (dbm@umn.edu) America during summer. We reproduce this correlation and slope in the model with the reduced plant source, which also confirms that the anthropogenic source of methanol must be small. Our reduced plant source also provides a better simulation of methanol observations over tropical South America.

Earth System Chemistry integrated Modelling (ESCiMo) with the Modular Earth Submodel System (MESSy) version 2.51

“…For methanol, the net oceanic sink is uncertain, ranging from 0.1 to 21 Tg (C) a −1 (Heikes et al, 2002;Galbally and Kirstine, 2002;Jacob et al, 2005), with a recent study by Millet et al (2008) resulting in an net oceanic methanol sink of 6 Tg (C) a −1 . The simulated oceanic uptake of methanol ranges from 1.2 to 1.85 Tg (C) a −1 (Fig.…”

“…Acetone (Fig. 22) shows the largest deviations, when comparing model results with measurements (for instrument specifics, see Neumaier et al, 2014). Tropospheric values are underestimated by about 60 to 100 % and the seasonal cycle of the measurement data is not visible.…”

Methanol emissions from maize: Ontogenetic dependence to varying light conditions and guttation as an additional factor constraining the flux

“…Field and laboratory measurements have been carried out to characterize methanol sources and sinks. By integrating this knowledge into global chemistry and transport models, global annual budgets have been constructed (Singh et al, 2000;Heikes et al, 2002;Galbally and Kirstine, 2002;Tie et al, 2003;von Kuhlmann et al, 2003;Jacob et al, 2005;Millet et al, 2008;Stavrakou et al, 2011). Terrestrial plants have been found to be a major source of atmospheric methanol, with an annual global emission ranging from 75 to 280 Tg y À1 and constituting 60e80% of the total source strength.…”

Production of methanol, acetaldehyde, and acetone in the Atlantic Ocean

“…Modeling studies have suggested that there must be a large marine in situ source of methanol in the ocean mixed layer [Millet et al, 2008], which is speculated to be biological in nature. For example, methanol has been observed in the gaseous headspace above laboratory phytoplankton cultures and in water surrounding intact macroalgal cells [Nightingale, 1991;Riemer, 1998].…”