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Sugar cane ethanol biofuel produces 10 times the pollution of gasoline and diesel

Posted By Joanne Nova On July 22, 2012 @ 2:33 pm In Global Warming | Comments Disabled

Indur Goklany calculated that biofuels policies killed nearly 200,000 people  in 2010 alone. That was before this study showed things may be worse than we suspected.

Brazil is the largest sugar cane ethanol producer in the world, but people are burning four times the area of sugar cane plantations than previously realized, and it’s producing far more pollution than they thought. For every unit of energy generated, the ethanol-biofuel use produces a lot less CO2 (plant fertilizer) but more volatile organic compounds (VOC’s), more carbon monoxide, more nitrous oxides, as well as more sulphur dioxides. (See Graph b below).

Compared to gasoline and diesel, over its whole life cycle, every unit of energy produced with sugar cane produces 10 times as much volatile organic compounds (VOC’s), carbon monoxide,  and nitrous oxides.  The amount PM10′s and PM2.5′s produced with ethanol fuels is even higher. Most of the pollution comes from burning fields of sugar cane (see graph a). Hence the people suffering the most from ethanol production will be villagers and rural farmers living near areas of sugar cane production. While there have been efforts to encourage farmers to produce cane without burning fields, over half of sugar-cane crop loads continue to be burned. Presumably there is a cost to producing sugar cane without burning. Perhaps sugar-cane production is viable and competitive without burning but this study does not discuss the reasons farmers prefer to burn fields.

If you care about pollution, and want less of it, and you care about the health of people in developing countries then clearly we should encourage gasoline and diesel use, and discourage production of ethanol that involves burning sugar cane-fields.

Likewise, to promote growth in the Amazon (by increasing CO2 levels), we ought to be burning fossil fuels and not fields of cane.

 If global policies devalue concentrated energy underground and prize diffuse photosynthetic sources of energy above ground, will we protect and retain dirty rocks deep below the surface at the expense of biodiversity and health of plants and people? It seems so.

 

Graph comparing emissions from biofuels to car use, diesel, gasoline

Figure 1  Comparisons of life-cycle emissions for sugar-cane ethanol in Brazil and conventional liquid fuels. a, Life-cycle emissions per unit energy of sugar-cane ethanol produced within five life-cycle phases. Although our life-cycle emissions account for a mix of sugar-cane fields where the burning practice is used and not used, the burning-phase emissions shown here are for ethanol produced from croplands that are burned. T/D, transportation/distribution; BTU, British thermal units. b, Comparisons of life-cycle emissions for conventional gasoline, diesel and sugar-cane ethanol. Estimates from the GREET model include six air pollutants (VOC, CO, NOx, PM10, PM2:5, and SOx) and greenhouse gases (as CO2 equivalent, CO2e). Right axis is for greenhouse-gas emissions.

The empirical evidence is consistent. Emissions of black carbon, organic carbon and carbonyl sulphide are rising rapidly over Brazil and the increase occurs during the months of peak sugar cane production.

graph of biofuels pollution increasing

….

What about other forms of biofuels?

Previously studies suggested that corn based ethanol had higher health and “climate-change” costs than gasoline, but that cellulosic ethanol production had lower costs. (Hill et al 2008) The cellulosic sources in that study were prairie biomass, Miscanthus, corn stover, or switchgrass, not sugar-cane.

Corn ethanol fares poorly relative to alternatives because it requires, per unit of fuel produced, more fossil fuel and fertilizer inputs that emit large amounts of GHG and PM2.5. Corn-ethanol emissions would be improved if the hypothesized advances in technology were to occur (i.e., reduced fertilizer inputs, increased yields on farm, and improved conversion), making combined environmental costs from corn ethanol by using natural gas for process heat similar to gasoline. Compared with corn ethanol, cellulosic ethanol from corn stover or perennial crops requires lower inputs and has lower emissions at the biorefinery because lignin combustion provides process heat and power, thereby displacing fossil fuel inputs and electricity production. “

Abstract of Tsao et al 2012:

Accelerating biofuel production has been promoted as an opportunity to enhance energy security, offset greenhouse gas
emissions and support rural economies. However, large uncertainties remain in the impacts of biofuels on air quality
and climate1,2. Sugar-cane ethanol is one of the most widely used biofuels, and Brazil is its largest producer3. Here we
use a life-cycle approach to produce spatially and temporally explicit estimates of air-pollutant emissions over the whole life
cycle of sugar-cane ethanol in Brazil. We show that even in regions where pre-harvest field burning has been eliminated
on half the croplands, regional emissions of air pollutants continue to increase owing to the expansion of sugar-cane
growing areas, and burning continues to be the dominant life-cycle stage for emissions. Comparison of our estimates of
burning-phase emissions with satellite estimates of burning in São Paulo state suggests that sugar-cane field burning is
not fully accounted for in satellite-based inventories, owing to the small spatial scale of individual fires. Accounting for
this effect leads to revised regional estimates of burned area that are four times greater than some previous estimates. Our revised emissions maps thus suggest that biofuels may have larger impacts on regional climate forcing and human health than previously thought.

Other information on Biofuels

References

Hill, J., Polasky, S., Nelson, E., Tilman, D., Huo, H., Ludwig, L., Neumann, J., Zheng, H. and Bonta, D. 2009. Climate change and health costs of air emissions from biofuels and gasoline. Proceedings of the National Academy of Sciences USA 106: 2077-2082. [Full text]

Tsao, C.-C., Campbell, J.E., Mena-Carrasco. M., Spak, S.N., Carmichael, G.R. and Chen, Y. 2011. Increased estimates of air-pollution emissions from Brazilian sugar-cane ethanol. Nature Climate Change 2: 53-57. [abstract]

h/t to NIPCC see their discussion of this paper.

Thanks to Mark in Perth for assistance.

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