Ambient Concentrations of Ethanol and Methyl tert-Butyl Ether in Porto Alegre, Brazil, March 1996−April 1997

Abstract

While air quality and other perceived benefits of oxygenated fuel programs are currently the topic of much debate, there are very few reports of ambient concentrations of oxygenated fuels (e.g., ethanol) and fuel additives (e.g., ethanol, methyl tert-butyl ether, hereafter called MTBE) in urban air. Ambient concentrations of MTBE and ethanol have been measured by GC−FID and GC−MS analysis of samples collected in electropolished canisters at a downtown location in Porto Alegre, Brazil, where 17% of the vehicles run on ethanol, 74% run on a mixture of 85% gasoline and 15% MTBE, and 9% use diesel fuel. During the ca. 1-year period of March 20, 1996−April 16, 1997, ambient levels of MTBE ranged from 0.2 to 17.1 ppbv (average = 6.6 ± 4.3 ppbv); those of ethanol ranged from 0.4 to 68.2 ppbv (average = 12.1 ± 13.3 ppbv). Ambient levels of ethanol and MTBE are compared to those of carbon monoxide (for which vehicle exhaust accounts for ca. 99% of total emissions in the city of Porto Alegre) and of acetylene. Linear regression of the ambient concentration data (44 samples) yielded near-zero intercepts and slopes of 11.40 ± 0.45 for acetylene (ppbv) vs CO (ppmv), 1.73 ± 0.20 for MTBE (ppbv) vs CO (ppmv), 0.153 ± 0.016 for MTBE (ppbv) vs acetylene (ppbv), and 4.64 ± 0.78 for ethanol (ppbv) vs CO (ppmv). These slopes together with an estimated vehicle exhaust emission rate for CO in mid-1996 are used to estimate vehicle emission rates of 2338 ± 393 t/year for ethanol and 1668 ± 193 t/year for MTBE.

Emission and Fate Assessment of Methyl Tertiary Butyl Ether in the Boston Area Airshed Using a Simple Multimedia Box Model: Comparison with Urban Air Measurements

“…In long-term monitoring experiments in the temperate regions of Porto Alegre, Brazil, and Glassboro, NJ, investigators found little correlation between measured MTBE concentrations in urban air and seasonality. 7,50 Because other seasonally dependent factors may also have been important in these cases, it can only be concluded that the relationship between seasonal temperature variation and nontailpipe emission rates is uncertain.…”

“…Although it is significantly smaller than any of these metropolitan giants, Porto Alegre, Brazil (which is similar in size to Boston, having a population of ϳ3 million, including suburban districts) had measured ambient MTBE air concentrations of 24 Ϯ 16 g/m 3 , based on year-round measurements from 1996 to 1997. 7 MTBE air concentrations in more remote suburbs or mid-sized urban areas are generally lower but range more widely, typically from 0.5 to 10 g/m 3 , based on measure- It is also worth noting that Grosjean et al 7 observed strong year-round correlations between measured MTBE concentrations and urban air concentrations of other gasoline combustion-related species such as carbon monoxide (CO) (r 2 ϳ 0.80) and acetylene (r 2 ϳ 0.83), suggesting that MTBE emission rates are strongly linked to total traffic volume. MTBE is not only volatile but is also relatively soluble in water (Table 1), thereby posing a contamination threat to water supplies from leaking underground fuel tanks and gasoline spills.…”

Observational constraints on the global atmospheric budget of ethanol

“…Future increases in ethanol emissions may impact the oxidizing capacity and the ozone-forming potential of the atmosphere (Singh et al, 2001). High levels of ethanol have been measured in the boundary layer in urban (ranging from 0.4 to 240 ppbv) (Grosjean et al, 1998;Nguyen et al, 2001;Millet et al, 2005), rural (0.04-0.4 ppbv) (Millet et al, 2004(Millet et al, , 2006, and remote (0.02-0.2 ppbv) (Singh et al, 2001) atmospheres. While ethanol-gasoline blended fuels have been advocated for reducing carbon monoxide emissions (Poulopoulos et al, 2001), their combustion also increases ambient levels of acetaldehyde and peroxyacetyl nitrate (PAN) (Tanner et al, 1988;Knapp et al, 1998;Jacobson, 2007), both of which are toxic and contribute to ozone pollution.…”

First measurements of methyl tert-butyl ether (MTBE) in the ambient air in San Jose, Costa Rica

“…Applied methodology has been previously described by other authors [7][8][9]. The detection limit of the method was set on 0.1 ppbv (0.4 µg m -3 ) for an air volume of 2.0 L. Samples with values below detection limit were assigned a value of half the detection limit for calculations.…”

“…In October, MTBE's concentrations were in the range from below 0.1 to 7.0 ppbv, with an average concentration of 1.0 ± 0.1 ppbv, whereas in November and December, MTBE levels were in the range from below 0.1 to 1.9 ppbv, with an average concentration of 0.8 ± 0.1. These average concentrations, expressed on mass per volume concentration units, corresponds to 3.6 and 2.9 µg m -3 , which are useful to estimate relative human exposure to MTBE [9].…”