Global Budget of Methanol: Constraints from Atmospheric Observations

Institute for Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Tyrol, Austria
Journal of Geophysical Research 04/2005; 110(D8). DOI: 10.1029/2004JD005172
Source: OAI


We use a global three-dimensional model simulation of atmospheric methanol to examine the consistency between observed atmospheric concentrations and current understanding of sources and sinks. Global sources in the model include 128 Tg yr−1 from plant growth, 38 Tg yr−1 from atmospheric reactions of CH3O2 with itself and other organic peroxy radicals, 23 Tg yr−1 from plant decay, 13 Tg yr−1 from biomass burning and biofuels, and 4 Tg yr−1 from vehicles and industry. The plant growth source is a factor of 3 higher for young than from mature leaves. The atmospheric lifetime of methanol in the model is 7 days; gas-phase oxidation by OH accounts for 63% of the global sink, dry deposition to land 26%, wet deposition 6%, uptake by the ocean 5%, and aqueous-phase oxidation in clouds less than 1%. The resulting simulation of atmospheric concentrations is generally unbiased in the Northern Hemisphere and reproduces the observed correlations of methanol with acetone, HCN, and CO in Asian outflow. Accounting for decreasing emission from leaves as they age is necessary to reproduce the observed seasonal variation of methanol concentrations at northern midlatitudes. The main model discrepancy is over the South Pacific, where simulated concentrations are a factor of 2 too low. Atmospheric production from the CH3O2 self-reaction is the dominant model source in this region. A factor of 2 increase in this source (to 50–100 Tg yr−1) would largely correct the discrepancy and appears consistent with independent constraints on CH3O2 concentrations. Our resulting best estimate of the global source of methanol is 240 Tg yr−1. More observations of methanol concentrations and fluxes are needed over tropical continents. Better knowledge is needed of CH3O2 concentrations in the remote troposphere and of the underlying organic chemistry. Earth and Planetary Sciences Version of Record

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    • "For many years, methanol has been known as a growth stimulator for algae and higher plants (Fall and Benson 1996). Being one of the most abundant volatile organic compounds in the atmosphere (Jacob et al. 2005), methanol is emitted by plants (approximately 100 Mt year −1 ) during their growth as a result of cell wall reorganization involving pectin methylesterase (Isidorov et al. 1985; MacDonald and Fall 1993). As an inexpensive carbon source, methanol could be used for the increase in production of plant biomass especially algae. "
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    ABSTRACT: Methanol in low concentrations can stimulate the mixotrophic growth of some microscopic algae. The aim of the present work was to investigate the effect of methanol on the growth, photosynthesis, and respiration rate as well as free amino acid and soluble protein content in the cells of unicellular green alga Chlamydomonas reinhardtii. It was shown that 30–100 mM methanol induced an increase in C. reinhardtii biomass production compared to controls without the solvent. The packed cell volume was increased maximally by 35 % after growing for 6 days in the presence of 50 mM methanol. The effect was light-dependent, although the rate of photosynthesis changed insignificantly while the rate of respiration increased. The intracellular content of reduced nicotinamide coenzyme NAD(P)H also increased after methanol addition in the light. The intracellular content of free amino acids increased by 31 % as a result of 50 mM methanol addition, and their composition changed: glutamic acid, glutamine, alanine, serine, and tyrosine increased and methionine content decreased. The content of soluble protein also increased by 30 %, eliminating the possibility of proteolysis. Thus, methanol has a positive effect on nitrogen assimilation as indicated by the increase in the content of soluble proteins and free amino acids. This effect may be connected with methanol-induced stimulation of respiration and the light-dependent increase in NAD(P)H content. The results suggest that methanol not only is a carbon source for C. reinhardtii cells but also can take part in energy metabolism.
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    • "Methanol has reasonably long lifetime in the atmosphere therefore, the transport from biomass burning and biogenic sources outside the city can be significant contributors (Jacob et al., 2005). "
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    ABSTRACT: This study is based on the high mass and time-resolved measurements of seven VOCs using PTR-TOF-MS instrument at an urban site of India during winter 2013. Daily levels of OVOCs and aromatics were in the ranges of 3.5-37 ppbv and 0.85-23 ppbv, respectively with OVOCs accounted for up to 80% of total measured VOCs. Impact of long-range transport from the polluted Indo-Gangetic Plain and clean Thar desert was observed during the episodes of high and low VOCs, respectively. VOCs exhibited strong diurnal variations with peaks during morning and evening hours and lowest in afternoon. Relatively elevated aromatics during evening hours coincided with the lowest-OVOCs indicating influence of fresh vehicular emissions. Emission ratios of isoprene and OVOCs with respect to benzene followed the diurnal cycles of temperature and solar flux indicating role of biogenic and photochemical processes, respectively. Correlation study of VOCs with benzene suggests major contribution from anthropogenic and also from biogenic and secondary sources to some extent. The higher emissions ratios of ∆methanol/∆acetonitrile correspond to the episodes of long-range transport from biomass burning sources located in the Indo-Gangetic Plain (IGP). In addition to the pattern of emission, the diurnal and day-to-day variations of VOCs were influenced by the local meteorological conditions and depth of planetary boundary layer (PBL).
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    • "do account for deposition to land and the oceans in addition to the OH sink, but emission and deposition are treated separately , which likely results in inconsistencies (Singh et al., 2000; Galbally and Kirstine, 2002; Heikes et al., 2002; Tie et al., 2003; von Kuhlmann et al., 2003a, b; Jacob et al., 2005; Millet et al., 2008; Stavrakou et al., 2011). The prominent role of deposition is an emerging feature of ecosystem-scale measurements and is in contrast to leaf-level work that has almost exclusively reported methanol emissions and focussed on describing the corresponding controls (e.g. "
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    ABSTRACT: Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of living plants as the major source and the reaction with OH as the major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates reflecting uncertainties in the approaches used to model, and the empirical data used to separately constrain these terms. Here we compiled micrometeorological methanol flux data from eight different study sites and reviewed the corresponding literature in order to provide a first cross-site synthesis of the terrestrial ecosystem-scale methanol exchange and present an independent data-driven view of the land-atmosphere methanol exchange. Our study shows that the controls of plant growth on the production, and thus the methanol emission magnitude, and stomatal conductance on the hourly methanol emission variability, established at the leaf level, hold across sites at the ecosystem-level. Unequivocal evidence for bi-directional methanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the formation of surface wetness. Methanol may adsorb to or dissolve in this surface water and eventually be chemically or biologically removed from it. Management activities in agriculture and forestry are shown to increase local methanol emission by orders of magnitude; they are however neglected at present in global budgets. While contemporary net land methanol budgets are overall consistent with the grand mean of the micrometeorological methanol flux measurements, we caution that the present approach of simulating methanol emission and deposition separately is prone to opposing systematic errors and does not allow taking full advantage of the rich information content of micrometeorological flux measurements.
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