Letterst Biodiesel concerns I am writing to comment on the editorial “Biofuels and the environment” (Environ. Sci. Technol. 2006, 40, 4042). In your editorial you mainly discuss the economics of using ethanol and biodiesel from agricultural crops, with the conclusion that with present-day technology, ethanol from corn is not economically feasible. I have no quarrel with that conclusion and think that ethanol in gasoline is without serious public-health effects. However, I do have grave concerns about the suitability of so-called biodiesel (methyl esters of organic fatty acids), mainly from a public-health rather than an economic point of view. I have published several papers arguing that the usage of methyltert-butyl ether (MTBE)—or other methyl ethers, such as tert-amyl methyl ether—in gasoline contributed a highly toxic compound to the
New source performance standards for greenhouse gases The world is struggling with how to mitigate global warming caused by greenhouse gas emissions. The Intergovernmental Panel on Climate Change (IPCC) estimated the various emission scenarios that would lead to stabilization of CO2 concentrations in the atmosphere in the 350–790 ppm range by the year 2100 (1). The Framework Convention on Climate Change, which convened in Kyoto in 1997, agreed that by the year 2010 the developed countries will reduce their CO2 emissions by 6–8% below 1990 emission levels. It seems to me that instead of imposing such numerical goals for atmospheric concentrations or emission levels, each country should
ambient air. Not only was this toxic compound overlooked, but it was apparently responsible for the widely discussed epidemic of asthma in various parts of the U.S. At the 2006 annual meeting of the Air & Waste Management Association (AWMA) in New Orleans, I presented considerable evidence that MTBE in gasoline creates methyl nitrite in the exhaust. In addition, I showed various kinds of epidemiological evidence that this led to astonishing increases in asthma in U.S. cities whose gasoline was oxygenated with large amounts of MTBE. I also presented a brief review of the toxicology of the alkyl nitrites, with the conclusion that induction of asthma was a result that could be anticipated. I also noted that previous studies of the toxicology of MTBE are irrelevant, because it is the nitrite, not the ether, that is suspected of causing this problem. This (10-page) paper is available from the AWMA office in Pittsburgh
for a small fee, or it can be obtained for free from me via email. Fortunately, the usage of MTBE in U.S. gasoline is now a thing of the past. However, the detailed chemistry of the model that I presented also predicts that methyl esters (hence biodiesel) may also produce methyl nitrite. In both cases, the underlying chemistry is the same—pyrolysis of the ether or ester into methoxy radicals in the exhaust pipe. These ideas clearly need to be tested with laboratory studies of the presence of methyl nitrite in the exhaust of engines with the ether or ester in the fuel. Unfortunately, funding for such research has not been available in the U.S., largely because the environmental science community has little awareness of the very serious issues involved.
impose performance standards for major emitting sources of greenhouse gases. This is akin to the New Source Performance Standards (NSPS) imposed by the U.S. Clean Air Act Amendments of 1977 and implemented through the U.S. EPA. The NSPS did away with numerical emission standards for certain pollutants (e.g., particulate matter, sulfur oxides, nitrogen oxides [NOx ], carbon monoxide, and hazardous air pollutants) emitted by significant industrial categories (SIC). Instead, EPA mandated that each SIC implement the best available control technology (BACT) for reducing the emissions of such air pollutants through the best system of continuous emission reduction, taking into account the cost. BACT can change from time to time as new technologies become available that are superior to current BACT. For example, the current
BACT for particulate matter for power plant and industrial boilers is the electrostatic precipitator; for sulfur oxides, the wet or dry scrubber with pulverized lime or limestone; and for NOx, the low-NOx burner. For reducing CO2 emissions from coal-fueled power plant and industrial boilers, current assessments consider three technological approaches: postcombustion capture of CO2 by chemical absorbents (e.g., monoethanolamine); oxyfuel combustion in which the fuel is combusted in pure oxygen, so that the combustion products consist mainly of CO2 and water vapor; and precombustion capture of CO2. The latter is envisioned for integrated coal gasification combined cycle (IGCC) power plants, in which coal is gasified into H2 and CO2. The former is used in a gas turbine for power production (or transportation fuel); the latter is
6878 n Environmental Science & Technology / October 15, 2007
PETER JOSEPH University of Pennsylvania
[email protected] © 2007 American Chemical Society
captured. The captured CO2 can be sequestered in deep geologic formations or in the deep ocean. Each country may select the appropriate BACT for new power plants and industrial boilers. Unfortunately, none of the three technologies is suitable for retrofitting, so only new sources will come under BACT for CO2 emission reduction. Grandfathering of existing sources must be strictly limited (e.g., fossil-fueled power plants must be replaced by new plants after a stipulated lifetime of the old ones). BACT can also be designed for transportation vehicles and other distributed emission sources. Because it is hard to conceive of CO2 capture technologies for automobiles and other noncentralized emission sources, BACT must inevitably include other metrics (e.g., fuel mileage, fuel mix, hybrids, and plug-ins). BACT for CO2
emissions from oil and gas wells may include a ban on flaring, separation of associated CO2 from the oil or gas, and capture and reinjection of the CO2 into the wells or other geologic formations. Other greenhouse gases may also have their BACT. For example, landfill methane cannot be vented into the atmosphere, coal-bed methane must be captured, and nitrous oxide has to be captured at nylon and fertilizer factories and cannot be used for nonessential activities (e.g., as a foaming agent for whipped cream). Chlorofluorocarbon (CFC) manufacturing is already banned worldwide, and hopefully CFCs will slowly disappear from the atmosphere. The advantage of BACT is not only that it reduces greenhouse gas emissions but also that for each country, and for each SIC within a country, BACT can be selected that is appro-
priate for the country and its emission sources of greenhouse gases. Perhaps the IPCC or the UN Environment Programme can supervise and monitor that appropriate BACT is implemented by each country, so that worldwide emission targets rather than ambient concentrations are achieved within a specified time frame. The disadvantage of BACT is that it pertains only to new sources. Interim emission reductions must be achieved by other means, such as conservation and efficiency improvement measures and use of noncarbon fuels and energy. DAN GOLOMB University of Massachusetts Lowell
[email protected] (1) IPCC. Climate Change 2007: Mitigation of Climate Change, Summary for Policymakers; IPCC: Geneva, 2007.
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