Abstract
Abstract. The effect of fuel ethanol content (10, 85 and 100 %) on primary emissions and on subsequent secondary aerosol formation was investigated for a Euro 5 flex-fuel gasoline vehicle. Emissions were characterized during a New European Driving Cycle (NEDC) using a comprehensive set-up of high time-resolution instruments. A detailed chemical composition of the exhaust particulate matter (PM) was studied using a soot particle aerosol mass spectrometer (SP-AMS), and secondary aerosol formation was studied using a potential aerosol mass (PAM) chamber. For the primary gaseous compounds, an increase in total hydrocarbon emissions and a decrease in aromatic BTEX (benzene, toluene, ethylbenzene and xylenes) compounds was observed when the amount of ethanol in the fuel increased. In regard to particles, the largest primary particulate matter concentrations and potential for secondary particle formation was measured for the E10 fuel (10 % ethanol). As the ethanol content of the fuel increased, a significant decrease in the average primary particulate matter concentrations over the NEDC was found. The PM emissions were 0.45, 0.25 and 0.15 mg m−3 for E10, E85 and E100, respectively. Similarly, a clear decrease in secondary aerosol formation potential was observed with a larger contribution of ethanol in the fuel. The secondary-to-primary PM ratios were 13.4 and 1.5 for E10 and E85, respectively. For E100, a slight decrease in PM mass was observed after the PAM chamber, indicating that the PM produced by secondary aerosol formation was less than the PM lost through wall losses or the degradation of the primary organic aerosol (POA) in the chamber. For all fuel blends, the formed secondary aerosol consisted mostly of organic compounds. For E10, the contribution of organic compounds containing oxygen increased from 35 %, measured for primary organics, to 62 % after the PAM chamber. For E85, the contribution of organic compounds containing oxygen increased from 42 % (primary) to 57 % (after the PAM chamber), whereas for E100 the amount of oxidized organics remained the same (approximately 62 %) with the PAM chamber when compared to the primary emissions.
Highlights
Vehicular engine emissions are known to degrade air quality in urban areas
For E100, a slight decrease in particulate matter (PM) mass was observed after the potential aerosol mass (PAM) chamber, indicating that the PM produced by secondary aerosol formation was less than the PM lost through wall losses or the degradation of the primary organic aerosol (POA) in the chamber
This study shows that the use of these fuels produces benefits by decreasing exhaust PM concentrations, having a positive influence on air quality
Summary
Vehicular engine emissions are known to degrade air quality in urban areas. Besides gaseous compounds (e.g. CO, NOx, hydrocarbons and volatile organic compounds), vehicle exhaust contains significant amounts of primary particulate matter (PM) (e.g. Maricq, 2007; Keuken et al, 2013; Gordon et al, 2014a). Primary particulate matter refers to particles directly emitted from the engine, the fuel combustion process or the brakes that have not yet experienced any significant chemical transformation in the atmosphere. Delayed primary aerosol includes species like sulfuric acid which occur in tailpipe conditions in a gaseous phase but will condense or nucleate immediately when the exhaust is cooled and diluted without any significant chemical transformation in the atmosphere (Arnold et al, 2012; Rönkkö et al, 2013; Pirjola et al, 2015). In addition to primary emissions, large amounts of secondary particulate matter form after the exhaust gases are released into the atmosphere (Chirico et al, 2010). Secondary particulate matter forms in the atmosphere via gas-to-particle conversion as oxidation processes typically lower the volatility (vapour pressure) of gaseous compounds. While a large number of studies have focused on vehicular primary particulate emissions (Giechaskiel et al, 2005; Maricq, 2007; Lähde et al, 2010; Karjalainen et al, 2014), a relatively limited number of studies have focused on secondary emissions
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