China Makes Progress on Sulfur Dioxide Emissions
January 9, 2018
New UMD-led study indicates that
India may be world’s top sulfur dioxide emitter
dioxide is an air pollutant that causes acid rain, haze and many
health-related problems. It is produced predominantly when coal is
burned to generate electricity.
Although China and India remain the world’s largest consumers of coal, a
new University of Maryland-led study found that China’s sulfur dioxide
emissions fell by 75 percent since 2007, while India’s emissions
increased by 50 percent. The results suggest that India is becoming, if
it is not already, the world’s top sulfur dioxide emitter.
“The rapid decrease of sulfur dioxide emissions in China far exceeds
expectations and projections,” said Can Li, an associate research
scientist in UMD’s Earth System Science Interdisciplinary Center and
first author on the study. “This suggests that China is implementing
sulfur dioxide controls beyond what climate modelers have taken into
The study was published in the journal Scientific Reports on November 9,
China and India are the world’s top consumers of coal, which typically
contains up to 3 percent sulfur. Most of the two countries’ sulfur
dioxide emissions come from coal-fired power plants and coal-burning
factories. In particular, Beijing suffers from severe haze problems
because of the many coal-burning factories and power plants located
nearby and upwind.
Starting in the early 2000s, China began implementing policies such as
fining polluters, setting emission reduction goals and lowering
emissions limits. According to the results of the current study, these
efforts are paying off.
“Sulfur dioxide levels in China declined dramatically even though coal
usage increased by approximately 50 percent and electricity generation
grew by over 100 percent,” explained Li, who is also a research
associate at NASA’s Goddard Space Flight Center. “This suggests that
much of the reduction is coming from controlling emissions.”
Despite China’s 75 percent drop in sulfur dioxide emissions, recent work
by other scientists has shown that the country’s air quality remains
poor and continues to cause significant health problems. This may be
because sulfur dioxide contributes to only approximately 10 to 20
percent of the air particles that cause haze, according to Li.
“If China wants to bring blue skies back to Beijing, the country needs
to also control other air pollutants,” Li said.
By contrast, India’s sulfur dioxide emissions increased by 50 percent
over the past decade. The country opened its largest coal-fired power
plant in 2012 and has yet to implement emission controls like China.
“Right now, India’s increased sulfur dioxide emissions are not causing
as many health or haze problems as they do in China because the largest
emission sources are not in the most densely populated area of India,”
Li said. “However, as demand for electricity grows in India, the impact
To generate an accurate profile of emissions over India and China for
the current study, the researchers combined emissions data generated by
two different methods.
First, the researchers collected estimated emission amounts from
inventories of the number of factories, power plants, automobiles and
other contributors to sulfur dioxide emissions. These inventories, while
important data sources, are often incomplete, outdated or otherwise
inaccurate in developing countries. They also cannot account for
changing conditions or unforeseen policies.
The researchers’ second data source was the Ozone Monitoring Instrument
(OMI) on NASA’s Aura satellite, which detects a variety of atmospheric
pollutants including sulfur dioxide. While OMI can collect up-to-date
information and spot emission sources missing from the inventories, it
can only detect relatively large emission sources. In addition, clouds
or other atmospheric conditions can interfere with its measurements.
To overcome these challenges, the UMD and NASA scientists collaborated
with researchers from Environment and Climate Change Canada to develop
better algorithms to quantify emissions based on OMI data. In addition,
UMD Department of Atmospheric and Oceanic Science Professors Russell
Dickerson and Zhanqing Li, co-authors of the paper, used a weather
aircraft to measure the concentrations of sulfur dioxide and other air
pollutants over one of the most polluted regions in China. By comparing
these measurements with OMI data, the researchers verified the satellite
combining the OMI and inventory data, the researchers generated a more
accurate estimate than either data source alone. Previously published
studies, which relied on inventory data and published policies,
projected that China’s sulfur dioxide emissions would not fall to
current levels until 2030 at the earliest.
“Those studies did not reflect the true situation on the ground,” said
Li, who is also a member of the U.S. OMI Science Team. “Our study
highlights the importance of using satellite measurements to study air
quality, especially in regions where conditions may change rapidly and
Li hopes the current study’s results can be used to improve climate and
atmospheric models by providing more accurate input data.