Brazilian biofuels with LUC may have much higher non-GHG emissions than conventional gasoline and diesel
|Comparisons of life-cycle emissions from LUC phase for (a) sugar cane ethanol and (b) soybean biodiesel. Credit: ACS, Tsao et al. Click to enlarge.|
When including Land Use Change (LUC) factors, Brazilian sugar cane ethanol and soybean biodiesel have much larger life-cycle emissions than conventional gasoline and biodiesel for six regulated, non-greenhouse gas (GHG) air pollutants, according to a study led by a team from the University of California, Merced. The pollutants are NMHC, CO, NOx, TPM, PM2.5 and SOx.
Even with the application of the “Green Ethanol Protocol”—which will eliminate sugar cane pre-harvest burning in the future—Brazilian biofuels including sugar cane ethanol and soybean biodiesel are still likely to have higher air pollution impacts than conventional fossil fuels due to the LUC effects if the LUC occurs as projected through 2020, according to the researchers. A paper on their work is published in the ACS journal Environmental Science & Technology.
Expansion in Brazil presents unique opportunities for both liquid fuel and electricity production. Estimates of the life-cycle GHG emissions from biofuels are largely based on regional and global models of the land-use change (LUC) impacts from biofuels. The climate effects of land-use changes from increasing biofeedstock acreage, both indirect and direct, have dominated policy discussion, and focused on comparisons in long-lived GHGs. However, the potential for land-use change to also cause important non-GHG air pollution emissions (e.g., particulate matter, carbon monoxide) has been largely over-looked. These non-GHG air pollutants may also lead to short-term impacts on local and regional climate.
...Among the available biofuels on the market, sugar cane ethanol that is primarily produced in Brazil may result in lower life-cycle GHG emissions than other conventional biofuels such as corn ethanol. However, sugar cane ethanol may be of particular concern with respect to non-GHG air pollution due to pre-harvest burning of sugar cane fields. An additional driver of life-cycle non-GHG air pollution emissions from sugar cane ethanol may be the dLUC [direct land use change] and iLUC [indirect land use change] emissions that could be incurred by an expansion of biofuel croplands.—Tsao et al.
The emissions problem with LUC stems from the practices of open burning for land clearing, such as slash-and burn. In their paper, C.-C. Tsao and colleagues estimated spatially explicit emissions from direct and indirect LUC due to the future expansion of biofuels production in Brazil by using a bottom-up approach incorporating LUC maps, fuel loading, combustion completeness, and emission factors. They compared these emissions with other life-cycle phases and life-cycle emissions estimates for fossil fuels. They normalized LUC emissions based on three cases of production periods (20, 30, 100 years).
Among their findings were:
Non-GHG LUC emissions from sugar cane ethanol have the same magnitude as the emissions from other life-cycle stages but are higher than conventional gasoline for six regulated air pollutants in the case of 20- and 30-year production period. Even in the 100-year case, LUC emissions in CO and particulate matter are still higher than that of gasoline.
Life-cycle emissions of sugar cane ethanol with consideration of LUC effects (376−683 g PM2.5 emitted per mmBTU fuel depending on production periods) are 75−136 times higher than the life-cycle emissions of conventional gasoline (5 g PM2.5 emitted per mmBTU fuel).
Biodiesel has much higher emissions of six regulated air pollutants than conventional diesel. For example, biodiesel LUC emission for PM2.5 (515−2,575 g PM2.5 emitted per mmBTU fuel depending on production periods) is 103−515 times higher than diesel (5 g PM2.5 emitted per mmBTU fuel).
We found that LUC emissions, particularly iLUC (F2R) [forest-to-rangeland], associated with an incremental increase in the supply of biofuels may be significant under current burning practices, and if biofuels-driven iLUC is not avoided. According to our results, the planned reductions in pre-harvest burning will have positive impacts locally, but the LUC emissions will remain large unless deforestation (F2R) is eliminated. After LUC projections, the largest uncertainty in LUC emissions is from the CF [combustion factor, the fraction of fuel consumption relative to the total available fuel loading] for deforestation, ranging from 65% to 133% of baseline estimates. These LUC emissions may be under-estimated as the CFs used in the analysis are measured from wild or prescribed fires. The practices for LUC, unlike wild or prescribed fire, involve slash-and-burn to remove biomass. In some cases, additional burns may occur two or three more times if the first fire has not removed enough slash.
Other important sources of uncertainty for LUC emissions are the magnitude and spatial distribution of the areas of LUC. However, LUC projections are inherently highly uncertain. As a result, the results of our study are conditional on the specific LUC scenario applied here.
...These results suggest that careful management of LUC is essential for ensuring the sustainability of Brazilian biofuels and for preventing potential hazards from non-GHG air pollution.—Tsao et al.
C.-C. Tsao, J. E. Campbell, M. Mena-Carrasco, S. N. Spak, G. R. Carmichael, and Y. Chen (2012) Biofuels That Cause Land-Use Change May Have Much Larger Non-GHG Air Quality Emissions Than Fossil Fuels. Environmental Science & Technology doi: 10.1021/es301851x