Mitigating Ozone Pollution with Methane Emission Controls: Global Health Benefits
Research Team: Denise Mauzerall, Jason West (post-doc); Arlene Fiore, Larry Horowitz (GFDL scientists)
Methane (CH4) contributes to the growing global background concentration of tropospheric ozone (O3), an air pollutant associated with premature mortality, reductions in crop yields and ecosystem damage. Methane and O3 are also important greenhouse gases. Reducing methane emissions therefore decreases surface ozone everywhere while slowing climate warming. However, although methane mitigation has been considered to address climate change, it has not been targeted for air quality purposes. In our PNASpaper (West et al., 2006) we show that global decreases in surface ozone concentrations, due to methane mitigation, result in substantial and widespread decreases in premature human mortality. Reducing global anthropogenic methane emissions by 20% beginning in 2010 would decrease the average daily maximum 8-h surface ozone by ~1 part per billion by volume globally. By using epidemiologic ozone mortality relationships, this ozone reduction is estimated to prevent ~30,000 premature all-cause mortalities globally in 2030, and ~370,000 between 2010 and 2030. The marginal cost-effectiveness of this 20% methane reduction is estimated to be ~$420,000 per avoided mortality. If avoided mortalities are valued at $1 million each, the benefit is ~$240 per tonne of CH4 (~$12 per tonne of CO2 equivalent), which exceeds the marginal cost of the methane reduction. These estimated air pollution ancillary benefits of climate-motivated methane emission reductions are comparable with those estimated previously for CO2. We conclude that methane mitigation offers a unique opportunity to improve air quality globally and can be a cost-effective component of international ozone management, bringing multiple benefits for air quality, public health, agriculture, climate, and energy.
Publication
West, J. J., Fiore, A. F., Horowitz, L. W., Mauzerall, D. L., “Mitigating Ozone Pollution with Methane Emission Controls: Global Health Benefits,” Proceedings of the National Academy of Science, vol. 103, no. 11, March 14, 2006.
Maximizing climate benefits while reducing O3 precursors to improve air quality.
Research Team: Denise Mauzerall, Jason West (post-doc); Arlene Fiore, Vaishali Naik, Dan Schwarzkopf, Larry Horowitz (GFDL scientists)
Efforts to reduce O3 concentrations over continental regions usually focus on reductions in the emissions of nitrogen oxides (NOx=NO+NO2), carbon monoxide (CO) or non-methane volatile organic compounds (VOCs). Additional work of ours shows that although NOx reductions are effective at reducing O3 concentrations over continental regions they result in slight increases in radiative forcing (West et al., 2007). This is because reductions in NOx leads to reductions in the hydroxyl radical (OH), the chief atmospheric oxidant, which results in increases in CH4 lifetimes and concentrations. We examined the sensitivity of surface O3 concentrations and net radiative forcing of climate to reductions in emissions of four precursors – NOx, VOCs, carbon monoxide, and methane (CH4). We found that decreases in CH4 emissions cause the greatest decrease in net radiative forcing per unit reduction in surface O3, while NOx reductions slightly increase net radiative forcing (West et al., 2007). Our analysis thus lends additional support to policy efforts to reduce methane emissions. Of the available means to improve O3 air quality CH4 abatement best reduces climate forcing.
Publication
West, J.J., A.M. Fiore, V. Naik, L.W. Horowitz, M.D. Schwarzkopf, D.L. Mauzerall, Ozone Air Quality and Radiative Forcing Consequences of Changes in Ozone Precursor Emissions, Geophys. Res. Lett., 34, L06806, 2007.
Mitigation of Methane Emissions from Rice Paddies
Research Team: Denise Mauzerall, Shangping Xu (doctoral student/post doc), Peter Jaffe (CEE professor)
Methane is the second most important greenhouse gas after carbon dioxide. Rice paddy soils release approximately 15–20% of total methane emitted to the atmosphere. A process based methane emission model was developed for rice paddy systems that highlights plant mediated methane transport and permits examination of the effects of fertilizer application and field drainage on methane emissions. The model may be used on a national scale to establish national methane emission inventories from rice paddies and to evaluate the feasibility and cost-effectiveness of various mitigation options that could vary from site to site.
Publication
Xu, S., Jaffe, P., Mauzerall, D. L., “A Process-based Model for Methane Emission from Flooded Rice Paddy Systems,” Ecological Modeling, vol. 205, pp. 475-491, 2007.