Ethanol blends are even worse for air quality when used in cold temperatures yet are being promoted in areas like northern Europe where very low temperatures are common-Atmospheric Environment study, Sept. 2015

Sept. 2015, "Primary emissions and secondary organic aerosol formation from the exhaust of a flex-fuel (ethanol) vehicle," Atmospheric Environment, sciencedirect.com, R. Suarez-Bertoa^{a, ,} et al.

"Abstract

Incentives to use biofuels may result in increasing vehicular emissions of compounds detrimental to air quality. Therefore, regulated and unregulated emissions from a Euro 5a flex-fuel vehicle, tested using E85 and E75 blends (gasoline containing 85% and 75% of ethanol (vol/vol), respectively), were investigated at 22 and −7 °C over the New European Driving Cycle, at the Vehicle Emission Laboratory at the European Commission Joint Research Centre Ispra, Italy. Vehicle exhaust was comprehensively analyzed at the tailpipe and in a dilution tunnel. A fraction of the exhaust was injected into a mobile smog chamber to study the photochemical aging of the mixture. We found that emissions from a flex-fuel vehicle, fueled by E85 and E75, led to secondary organic aerosol (SOA) formation, despite the low aromatic content of these fuel blends. Emissions of regulated and unregulated compounds, as well as emissions of black carbon (BC) and primary organic aerosol (POA) and SOA formation were higher at −7 °C. The flex-fuel unregulated emissions, mainly composed of ethanol and acetaldehyde, resulted in very high ozone formation potential and SOA, especially at low temperature (860 mg O₃ km⁻¹ and up to 38 mg C kg⁻¹). After an OH exposure of 10 × 10⁶ cm⁻³ h, SOA mass was, on average, 3 times larger than total primary particle mass emissions (BC + POA) with a high O:C ratio (up to 0.7 and 0.5 at 22 and −7 °C, respectively) typical of highly oxidized mixtures. Furthermore, high resolution organic mass spectra showed high 44/43 ratios (ratio of the ions m/z 44 and m/z 43) characteristic of low-volatility oxygenated organic aerosol. We also hypothesize that SOA formation from vehicular emissions could be due to oxidation products of ethanol and acetaldehyde, both short-chain oxygenated VOCs, e.g. methylglyoxal and acetic acid, and not only from aromatic compounds.

1. Introduction

The use of biofuels is increasing worldwide as a result of a promotion to meet the growing demand of transport related energy as well as to reduce greenhouse gas (GHG) emissions (European Commission, 2009). Biofuels were seen as a measure to reduce emissions of GHGs from road transport because they were considered CO₂ neutral.

The EU has set a target of 10% share of renewable energy in the transport sector, to be complied with by 2020 (2009/28/EC). Biofuels covered 4.3% of this share in 2010 (80% biodiesel, 20% ethanol) (European Commission, 2013).

Previous studies have suggested that increasing ethanol content in fuel blends reduces the emission of some regulated gases (CO and total hydrocarbons, THC) and CO₂ (Clairotte et al., 2013, Durbin et al., 2007, Graham et al., 2008 and Andrade et al., 1998). However, despite promising benefits in terms of reducing regulated compounds and CO₂ emissions, it has been shown that higher ethanol concentrations in fuel blends lead to higher emissions of ethanol and carbonyl compounds, mainly acetaldehyde, which are associated with urban air pollution and the formation of persistent pollutants (Clairotte et al., 2013, Durbin et al., 2007, Graham et al., 2008 and Andrade et al., 1998). In the atmosphere, ethanol is a precursor of acetaldehyde and peroxyacetyl nitrate (PAN); hence, a change in the ethanol emissions will affect atmospheric composition and chemistry. Photochemical oxidation by OH radicals is the main atmospheric sink of ethanol (Atkinson et al., 2006). Ethanol's atmospheric life time is about 4 days (Atkinson et al., 2006), with acetaldehyde being the main oxidation product at ∼95% yield. Acetaldehyde is classified as a hazardous air pollutant by the U.S. EPA (Chemical Summary for Acetaldehyde), and its subsequent oxidation can also lead to production of ozone (O₃) and PAN. Thus, the fate of atmospheric reactive nitrogen (NOy) could be affected by an increase in the PAN to NOy ratio (Millet et al., 2012a). Moreover, modeling studies have reported that in the case of a considerable shift from gasoline to ethanol blends, urban ozone levels would increase (Cook et al., 2011, Diana and Mark, 2012 and Jacobson, 2007).

Previous studies have shown that, while in some metropolitan areas formaldehyde is almost always the predominant carbonyl emitted by vehicles (acetaldehyde/formaldehyde ratio emitted <1 b=""> for Brazilian cities acetaldehyde/formaldehyde ratios

are ≥1 (Corrêa et al., 2003, Nguyen et al., 2001 and Corrêa et al., 2010). This behavior has been attributed to the use of ethanol and gasohol (gasoline with 24% of ethanol content) as fuels (Corrêa et al., 2003, Nguyen et al., 2001 and Corrêa et al., 2010). Incomplete combustion of ethanol results in higher acetaldehyde emission compared to formaldehyde. Carbonyl compounds are among the main volatile organic compounds (VOCs) present in the atmosphere of cities where ethanol blended fuels are used (Corrêa et al., 2010). They are also the main ozone precursors in those cities (Corrêa et al., 2010).

Atmospheric reactions of VOCs have been of great interest for the study of secondary organic aerosol (SOA) formation. SOA is a major contributor to airborne particulate matter (Hallquist et al., 2009), which is associated with adverse health effects (Pope et al., 2002). SOA not only impoverishes air quality but also has an impact on climate via scattering and, absorption of light as well as aerosol–cloud interactions (Ramaswamy et al., 2007, Orlando et al., 1999 and Saleh et al., 2014)....

4. Conclusions

The results obtained in our study show that widespread use of vehicles running on high ethanol-content fuel blends, E85 and E75, needs to be thoroughly evaluated due to the negative effects that their emissions may have on urban air quality....

Emissions factors of all the compounds studied increased at the lower temperature. The FFV emissions resulted in a high ozone formation potential (OFP), which was nearly 4 times higher at lower temperature (218 and 860 mg O₃ km⁻¹ at 22 and −7 °C, respectively)....These results show that SOA formation from vehicular exhaust can arise from the reaction and/or oxidation of small functionalized molecules such as acetaldehyde and ethanol and not only from aromatics, as it is often hypothesized....

The use of flex-fuel vehicles with high ethanol content fuel blends is being promoted in regions like northern Europe, where very low temperature is a common scenario. The extensive use of these vehicles at low temperature will result in high emissions of ethanol and acetaldehyde that may lead to large formation of O₃ and SOA....

Acknowledgments

The VELA staff is acknowledged for the skilful technical assistance, in particular M. Cadario, R. Colombo, G. Lanappe, P. Le Lijour, F. Muehlberger, and M. Sculati as well as Rene Richter from PSI. We acknowledge the financial support by the Swiss Federal Office for the Environment (FOEN), the Swiss Federal Roads Office (FEDRO) and the Swiss National Science Foundation (SAPMAV 200021_13016). The authors also acknowledge the MASSALYA instrumental platform (Aix Marseille Université, lce.univ-amu.fr) for the provision of the PTR-ToF-MS measurements used in this publication and the French Environment and Energy Management Agency (ADEME, Grant numbers 1162C0002 and 1262C0017)."




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