Observational constraints on the global atmospheric budget of ethanol

Abstract

Abstract. Energy security and climate change concerns have led to the promotion of biomass-derived ethanol, an oxygenated volatile organic compound (OVOC), as a substitute for fossil fuels. Although ethanol is ubiquitous in the troposphere, our knowledge of its current atmospheric budget and distribution is limited. Here, for the first time we use a global chemical transport model in conjunction with atmospheric observations to place constraints on the ethanol budget, noting that additional measurements of ethanol (and its precursors) are still needed to enhance confidence in our estimated budget. Global sources of ethanol in the model include 5.0 Tg yr −1 from industrial sources and biofuels, 9.2 Tg yr −1 from terrestrial plants, ∼0.5 Tg yr −1 from biomass burning, and 0.05 Tg yr −1 from atmospheric reactions of the ethyl peroxy radical (C 2 H 5 O 2 ) with itself and with the methyl peroxy radical (CH 3 O 2 ). The resulting atmospheric lifetime of ethanol in the model is 2.8 days. Gas-phase oxidation by the hydroxyl radical (OH) is the primary global sink of ethanol in the model (65%), followed by dry deposition (25%), and wet deposition (10%). Over continental areas, ethanol concentrations predominantly reflect direct anthropogenic and biogenic emission sources. Uncertainty in the biogenic ethanol emissions, estimated at a factor of three, may contribute to Correspondence to: V. Naik (vaishali.naik@noaa.gov) the 50% model underestimate of observations in the North American boundary layer. Current levels of ethanol measured in remote regions are an order of magnitude larger than those in the model, suggesting a major gap in understanding. Stronger constraints on the budget and distribution of ethanol and OVOCs are a critical step towards assessing the impacts of increasing the use of ethanol as a fuel.

Attraction of ambrosia beetles to ethanol baited traps in a Slovakian oak forest

“…This experiment also supports the results of other ambrosia beetle monitoring trials which have been conducted only a few times in Europe (Markalas & Kalapanida 1997;Bouget & Noblecourt 2005). Several studies suggest that ethanol is produced from fermentative processes when trees respond to a number of environmental stresses including flooding, drought, or high levels of pollutant gases (Kimmerer & Kozlowski 1982;Naik et al 2010). Low oxygen conditions arising in stressed trees can also lead to ethanol production and subsequent attack by bark and ambrosia beetles (Miller & Rabaglia 2009).…”

“…Several studies suggest that ethanol is produced from fermentative processes in trees in response to various environmental stresses including flooding, drought, or high levels of pollutant gases (Kimmerer & Kozlowski 1982;Montgomery & Wargo 1983;Naik et al 2010). The attraction of ambrosia beetles to ethanol is related to their preference for woody material that has sufficiently aged to allow anaerobic respiration to generate ethanol within the tissues (Graham 1968;Cade et al 1970;Moeck 1970;Lindelöw et al 1993;Miller & Rabaglia 2009).…”

Characterization of total ecosystem-scale biogenic VOC exchange at a Mediterranean oak–hornbeam forest

“…The average aerodynamic temperature T z 0 was estimated using a method described by Nemitz et al (2009) as…”

“…b Lifetime in the boundary layer according to Paulot et al (2011). c Atmospheric lifetime according to Naik et al (2010). d Tropospheric lifetime according to Jacob et al (2002).…”

Removal of atmospheric ethanol by wet deposition

“…Vehicle ethanol emissions may affect the acid‐generating capacity of atmospheric waters and the oxidizing capacity of the atmosphere through reactions with the hydroxyl radical [ Kieber et al , ]. Ethanol reaction with the hydroxyl radical increases acetaldehyde concentration which in turn increases the concentration of the secondary pollutant peroxyacetyl nitrate, both of which are linked to smog and ozone formation [ Naik et al , ; Hubbard et al , ; Salvo and Geiger , ; Suarez‐bertoa et al , ]. Recent changes in ethanol fuel generation have been rapid with the U.S. and Brazil increasing their production by ~3 and ~1.5 times, respectively, in the last decade [ Renewable Fuels Association (RFA) , ].…”