Gasoline Plus Ethanol Equals Bad Ozone

Effects of Ethanol (E85) versus Gasoline Vehicles on Cancer and Mortality in the United States
by M A R K Z . J A C O B S O N *Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305-4020

Ethanol use in vehicle fuel is increasing worldwide, but the potential cancer risk and ozone-related health consequences of a large-scale conversion from gasolineto ethanol have not been examined. Here, a nested global-through-urban air pollution/weather forecast model is combined with high-resolution future emission inventories,population data, and health effects data to examine the effect of converting from gasoline to E85 on cancer, mortality, and hospitalization in the United States as a whole and Los Angeles in particular. Under the base-case emissions cenario derived, which accounted for projected improvements in gasoline and E85 vehicle emission controls, it was found that E85 (85% ethanol fuel, 15% gasoline) may increase ozone-related mortality, hospitalization, and asthma by about 9% in Los Angeles and 4% in the United States as a whole relative to 100% gasoline.

Ozone increases in Los Angeles and the northeast were partially offset by decreases in the southeast. E85 also increased peroxyacetyl nitrate (PAN) in the U.S. but was estimated to cause little change in cancer risk. Due to its ozone effects, future E85 may be a greater overall public health risk than gasoline. However, because of the uncertainty in future emission regulations, it can be concluded with confidence only that E85 is unlikely to improve air quality over future gasoline vehicles.

Unburned ethanol emissions from E85 may result in a global-scale source of acetaldehyde larger than that of direct emissions.

In 1826, Samuel Morey (1762-1843) patented the first internal combustion engine, which ran on ethanol and turpentine. Since then, ethanol fuel has been used in all industrialized countries. Today, ethanol is being promoted as a clean andrenewable fuel that will reduce global warming, air pollution, and reliance on diminishing gasoline. These reasons have been used to justify subsidies and legislation encouraging ethanol use worldwide.

Life-cycle assessments to date, though, suggest that cornethanol’s effects on equivalent greenhouse gases emissions relative to gasoline are small, with an uncertain sign (1-8). Some of the same studies have hypothesized that ethanol from cellulose may result in lower net greenhouse-gasemissions than corn ethanol. Todate, though, this hypothesis has not been tested on a large scale.

With respect to air pollution, several studies have examined emission differences between gasoline and ethanol fueled vehicles (9-19). However, no study has examined the spatially varying effect on cancer or ozone-related illness throughout the United States that might result from aconversion to ethanol. Such a study is important because previous introductions of chemicals (e.g., tetraethyl lead, chlorofluorocarbons, DDT, dioxins) without an analysis led to damaging consequences. Air pollution (indoor plus outdoor) is also the seventh leading cause of death worldwide(20), so any change in fuel that could affect mortality should be examined prior to its implementation.

Here, a 3-D atmospheric computer model that treats chemical and radiative transformations, meteorology, and transport, is used with 2020 spatially resolved emissions data to calculate spatially varying chemical concentrations from gasoline and ethanol. The ambient concentrations are then combined with health effects and population data to determine health risks due to the fuels. Results are analyzed at high resolution in Los Angeles and coarser resolution in the whole United States.

The model used was the nested global-through-urbanGATOR-GCMOM (21-25), described in the Supporting Information. For Los Angeles, three nested domains were treated: global (4°-SN × 5°-WE), California (0.2° × 0.15°), and Los Angeles (0.045° × 0.05°); for the U.S., two domains were treated: global and U.S. (0.5° × 0.75°). Los Angelesresults are shown to test conclusions at higher resolutionthan in the U.S. Since Los Angeles has historically been themost polluted airshed in the U.S., the testbed for nearly allU.S. air pollution regulation, and home to about 6% of theU.S. population, it is also ideal for a more detailed study.

Simulations were run comparing future (ca. 2020) fleetsfueled by gasoline and E85, where E85 contains 85% ethanol and 15% gasoline. Since ethanol, itself, contains 5% gasolineas a denaturant, E85 is really 80% ethanol and 20% gasoline. E85 was examined since the large-scale replacement of gasoline would require a fuel with high ethanol content. 2020 was examined because flex-fuel cars replacing current gasoline vehicles, most of which cannot use E85, could substantially penetrate the U.S. vehicle fleet only by 2020.

Future anthropogenic emission inventories for gasoline and E85 vehicles were prepared from the 2002 U.S. National Emission Inventory (NEI) (26), which treats spatially dis-tributed point, area, and mobile onroad/nonroad emissions. Mobile emissions include evaporative and exhaust. Form-aldehyde, acetaldehyde, and 1,3-butadiene result from combustion in gasoline and E85 but not from evaporation(10). Benzene and ethanol result from both. Non-NEI natural emissions were also treated (Supporting Information). The only emissions perturbed due to E85 were vehicle emissions since exposure in populated areas is affected far more byvehicle exhaust than production of ethanol or gasoline.

Tables 1 and S4 (where “S” refers to Supporting Informa-tion) summarize the speciated 2020 “baseline” gasoline and “Case 1” E85 emission inventories used here for Los Angeles and the U.S., respectively. The 2020 gasoline inventory was prepared by reducing NEI evaporative and exhaust mobile gasoline and nongasoline emissions by 60%, which is consistent with two independent estimates. First, D. Streets (personal communication) derived speciated 2030: 2000 emission factors by sector and world region assuming IPCCSRES A1B and B1 emission scenarios. Table S2 shows the result for the U.S. transportation sector and indicates that an across-the-board mobile emission reduction for 2020 assumed here is conservative since it exceeds the 2030.

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