4 research outputs found
Can Switching from Coal to Shale Gas Bring Net Carbon Reductions to China?
To
increase energy security and reduce emissions of air pollutants and
CO<sub>2</sub> from coal use, China is attempting to duplicate the
rapid development of shale gas that has taken place in the United
States. This work builds a framework to estimate the lifecycle greenhouse
gas (GHG) emissions from China’s shale gas system and compares
them with GHG emissions from coal used in the power, residential,
and industrial sectors. We find the mean lifecycle carbon footprint
of shale gas is about 30–50% lower than that of coal in all
sectors under both 20 year and 100 year global warming potentials
(GWP<sub>20</sub> and GWP<sub>100</sub>). However, primarily due to
large uncertainties in methane leakage, the upper bound estimate of
the lifecycle carbon footprint of shale gas in China could be approximately
15–60% higher than that of coal across sectors under GWP<sub>20</sub>. To ensure net GHG emission reductions when switching from
coal to shale gas, we estimate the breakeven methane leakage rates
to be approximately 6.0%, 7.7%, and 4.2% in the power, residential,
and industrial sectors, respectively, under GWP<sub>20</sub>. We find
shale gas in China has a good chance of delivering air quality and
climate cobenefits, particularly when used in the residential sector,
with proper methane leakage control
Global Methane Emissions from Pit Latrines
Pit
latrines are an important form of decentralized wastewater
management, providing hygienic and low-cost sanitation for approximately
one-quarter of the global population. Latrines are also major sources
of the greenhouse gas methane (CH<sub>4</sub>) from the anaerobic
decomposition of organic matter in pits. In this study, we develop
a spatially explicit approach to account for local hydrological control
over the anaerobic condition of latrines and use this analysis to
derive a set of country-specific emissions factors and to estimate
global pit latrine CH<sub>4</sub> emissions. Between 2000 and 2015
we project global emissions to fall from 5.2 to 3.8 Tg y<sup>–1</sup>, or from ∼2% to ∼1% of global anthropogenic CH<sub>4</sub> emissions, due largely to urbanization in China. Two and
a half billion people still lack improved sanitation services, however,
and progress toward universal access to improved sanitation will likely
drive future growth in pit latrine emissions. We discuss modeling
results in the context of sustainable water, sanitation, and hygiene
development and consider appropriate technologies to ensure hygienic
sanitation while limiting CH<sub>4</sub> emissions. We show that low-CH<sub>4</sub> on-site alternatives like composting toilets may be price
competitive with other CH<sub>4</sub> mitigation measures in organic
waste sectors, with marginal abatement costs ranging from 57 to 944
/ton CO<sub>2</sub>e in Asia
Long-Lived Species Enhance Summertime Attribution of North American Ozone to Upwind Sources
Ground-level
ozone (O<sub>3</sub>), harmful to most living things, is produced
from both domestic and foreign emissions of anthropogenic precursors.
Previous estimates of the linkage from distant sources rely on the
sensitivity approach (i.e., modeling the change of ozone concentrations
that result from modifying precursor emissions) as well as the tagging
approach (i.e., tracking ozone produced from specific O<sub>3</sub> precursors emitted from one region). Here, for the first time, we
tag all O<sub>3</sub> precursors (i.e., nitrogen oxides (NO<sub><i>x</i></sub>), carbon monoxide (CO), and volatile organic compounds
(VOCs)) from East Asia and explicitly track their physicochemical
evolution without perturbing the nonlinear O<sub>3</sub> chemistry.
We show that, even in summer, when intercontinental influence on ozone
has typically been found to be weakest, nearly 3 parts per billion
by volume (ppbv) seasonal average surface O<sub>3</sub> over North
America can be attributed to East Asian anthropogenic emissions, compared
with 0.7 ppbv using the sensitivity approach and 0.5 ppbv by tagging
reactive nitrogen oxides. Considering the acute effects of O<sub>3</sub> exposure, approximately 670 cardiovascular and 300 respiratory premature
mortalities within North America could be attributed to East Asia.
CO and longer-lived VOCs, largely overlooked in previous studies,
extend the influence of regional ozone precursors emissions and, thus,
greatly enhance O<sub>3</sub> attribution to source region
Vehicle Emissions as an Important Urban Ammonia Source in the United States and China
Ammoniated
aerosols are important for urban air quality, but emissions
of the key precursor NH<sub>3</sub> are not well quantified. Mobile
laboratory observations are used to characterize fleet-integrated
NH<sub>3</sub> emissions in six cities in the U.S. and China. Vehicle
NH<sub>3</sub>:CO<sub>2</sub> emission ratios in the U.S. are similar
between cities (0.33–0.40 ppbv/ppmv, 15% uncertainty) despite
differences in fleet composition, climate, and fuel composition. While
Beijing, China has a comparable emission ratio (0.36 ppbv/ppmv) to
the U.S. cities, less developed Chinese cities show higher emission
ratios (0.44 and 0.55 ppbv/ppmv). If the vehicle CO<sub>2</sub> inventories
are accurate, NH<sub>3</sub> emissions from U.S. vehicles (0.26 ±
0.07 Tg/yr) are more than twice those of the National Emission Inventory
(0.12 Tg/yr), while Chinese NH<sub>3</sub> vehicle emissions (0.09
± 0.02 Tg/yr) are similar to a bottom-up inventory. Vehicle NH<sub>3</sub> emissions are greater than agricultural emissions in counties
containing near half of the U.S. population and require reconsideration
in urban air quality models due to their colocation with other aerosol
precursors and the uncertainties regarding NH<sub>3</sub> losses from
upwind agricultural sources. Ammonia emissions in developing cities
are especially important because of their high emission ratios and
rapid motorizations