Grappling with Ammonia in China’s Haze

Farms and Cars Contribute to Rising Levels of Noxious Gas

Chicken farmers and auto designers follow different career paths, but soon both may be changing how they do their jobs as part of a campaign to clean up China's polluted air.

Emissions from poultry waste and auto engines alike can contain potentially harmful levels of ammonia, a colorless gas with a pungent smell that's getting new attention as part of the country's battle against air pollution.

In August, the Ministry of Environmental Protection took a major step toward addressing the problem by issuing the central government's first-ever guidelines for ammonia emissions. Spearheading the drafting of Technical Guidelines for Compiling an Emissions List for Ammonia Sources (Trial) was a team of experts from Peking University led by Song Yu, an environmental study professor focusing on air pollution.

The guidelines were written to establish a list of major emission sources in order to better monitor ammonia output, based on international standards but tailored to China, Song said.

Meanwhile, local government environment bureaus are becoming increasingly aware of problems associated with ammonia emissions—and some are trying to reverse the trend. The Beijing Municipal Environmental Protection Bureau recently agreed to fund a research group to study ammonia sources and proposed potential government responses, said Peng Yingdeng, director of a research institute at the bureau.

In August, Beijing Municipal Research Institute of Environmental Protection invited bids for a research project that will monitor and analyze atmospheric and environmental ammonia levels in the air around chicken and cattle farms. The project, called Research into the Characteristics of Atmospheric Ammonia Emissions and Control Policies, is also expected to focus on potential measures for controlling the ammonia that's released when chemical fertilizers are spread on farm crops, and the characteristics of ammonia gas in the air above garbage dumps, water treatment facilities and major roads.

China is following in the footsteps of Western countries that have already taken steps to control ammonia emissions and "have recognized the importance of such measures in controlling particulate pollution in the atmosphere," said Liu Xuejun, a professor of environmental studies at China Agricultural University's Institute of Resources and Environment.

According to Song's team at the College of Environmental Sciences and Engineering, some 9.8 million tons of ammonia gas escaped into the atmosphere from the nation's farms, factories and vehicles in 2006. That was more than the total amount of ammonia given off that year in North America and Europe combined.

Indeed, China has been spewing more ammonia than any other country for the past 20 years.

According to a team led by atmospheric chemist Fabien Paulot at Harvard University, ammonia emissions from China averaged 10.2 million tons every year between 2005 and '08. U.S. emissions averaged 3.4 million tons, and the European Union's output was 3.7 million tons annually.

Left Off the List

Until now, the Chinese government has worked to curb dangerous emissions from coal-burning power plants, steel factories, construction-site dust, cars and other well-known sources of air pollution. The initiative has taken aim at the smog that has been increasing in most Chinese cities in recent years.

Limits on coal burning and auto emissions, better petroleum product refining methods, rules that require factories to cut sulfur and nitrate emissions, and getting contractors to control the dust that is kicked up at urban building sites are a few of the major achievements tied to the government's clean-up campaign.

So far, though, ammonia has been left off the official list of targeted pollutants, even though it is an increasingly serious component of smog.

"China now has objectives for reducing sulfur dioxide and nitrogen oxide emissions," said Liu. "But so far, they (government rules) have not included ammonia. Certainly, the next step will be to control ammonia."

Ammonia is a component in chemical fertilizers and explosives. When inhaled in concentrated doses, it can cause respiratory problems and potentially lead to cancer. In 2013, the International Agency for Research on Cancer, which is under the World Health Organization (WHO), said "air pollution is a leading environmental cause of cancer deaths." And a 2012 WHO report said 38 percent of the world's early deaths attributable to air pollution occur in China, with 1.24 million deaths in 2010 alone.

Scientists can determine ammonia's effect on air quality in a given area by measuring the density of airborne ammonium salts, which form when ammonia gas combines with the acids that are common in urban air.

Some researchers say that on heavily polluted days in some Chinese cities, ammonium sulfate and ammonium nitrate—two forms of ammonia salts—account for a large percentage of PM 2.5-type pollution. Concentrations of these chemicals rise in tandem with overall pollution levels.

Ammonium sulfate and ammonium nitrate account for less than one-fifth of the components in PM 2.5-type air pollution on days when smog levels are relatively light, according to Wang Yuesi, a research fellow at the Chinese Academy of Science's (CAS) Institute of Atmospheric Physics. But he said they can account for more than 40 percent on heavily polluted days.

PM 2.5 components include particulates usually carried into the air with smoke, and secondary particulate matter including ammonium sulfate and ammonium nitrate. These salts are formed by chemical reactions in the atmosphere, with their contribution to PM 2.5 higher during the summer than in winter.

Emissions from coal burning and autos oxidize in the atmosphere, turning to gaseous acids. Acids mixing with ammonia become ammonium sulfate and ammonium nitrate, contributing to smog.

"Ammonia in the atmosphere has an extremely important effect on the formation and increase of particulate matter," said Wang. "You could say it's a growth accelerant for atmospheric pollution."

Peng says ammonium salts together account for more than 30 percent of most PM 2.5-type pollution. And sometimes they comprise more than half.

"Today in Beijing, for example," Peng said on a recent weekday, "they accounted for more than 50 percent during the most serious period."

Many researchers think the problem is worse. Song said ammonium sulfate and ammonium nitrate account for about 30 percent of PM 2.5 pollution on lightly polluted days, and more than 60 percent when smog is heavy.

Researchers also think most of the country's ammonia pollution comes from farms where nitrogen fertilizer is spread on fields, or from the animal waste that piles up at poultry and livestock facilities. Factories also contribute some ammonia, but to a smaller degree.

Ammonia levels are rising in China, said Wang Shuxiao, director of the Atmospheric Pollution and Controls Institute at Tsinghua University's School of the Environment. He said that if these emissions continue growing at their current rate through 2015, ammonia will surpass sulfur dioxide—a major target of the central government's pollution control effort— in particulate density.

Researchers agree that excessive ammonia in China's urban areas is dangerous. Liu Xuejun at China Agricultural University's Institute of Resources and Environment, said severe salinization of the soil, particularly in northern China and mainly caused by drought, has caused ammonia concentrations to exceed acid gas concentrations in the atmosphere.

Song and his team found crop fertilizer and waste from cows, chickens, and other farm animals accounted for 87 percent of the nation's ammonia emissions. Liu estimated the combined contribution at more than 90 percent. Worldwide, about 80 percent of ammonia emissions come from livestock facilities and fertilizers.

Song said his figure was from 2006 and that he's "not clear whether there have been any great changes in the amount of agriculture and animal husbandry in China" since that year. "But I estimate that there haven't been great changes to the animal husbandry industry because people's standard of living has remained relatively stable. They eat meat when they it's called for and drink milk when it's called for. We need to take a look at changes in the use of chemical fertilizers."

Wang said factories and autos may play a larger role in ammonia pollution than many think.

"Runaway ammonia emissions from industry are on the rise," he said. "For example, power plants use a liquid ammonia spray in their denitration processes. It was initially expected that the ammonia would react with nitrogen oxides and form (harmless) nitrogen gas. But the reactions are not controlled well. Nitrogen gas is not formed, and ammonia comes out."

Auto engines give off ammonia, too. The central government's latest tailpipe emission standards require denitrators on all diesel engines. These use urea as a reactant that mixes with nitrogen oxides, is catalyzed by vanadium pentoxide, and then exits a tailpipe as nitrogen gas. But these devices often leak urea, which once free breaks down into ammonia.

Gas-powered engines also emit ammonia.

"The higher the grade of gasoline, the lower its sulfur content, meaning correspondingly higher amounts of ammonia emitted," said Wang.

According to a Ministry of Agriculture report, chemical fertilizer use and the livestock industry are slowing down in the Beijing-Tianjin-Hebei Province region. That should mean that ammonia emissions are decreasing, but Wang said that "in fact ammonia's density in the atmosphere is actually increasing."

This finding has led Wang's research group to suspect that some ammonia emissions sources are not linked to agriculture because they include factories and autos.

Wang further believes that agricultural ammonia emissions are approaching a turning point. Between 1976 and today, he noted, the nation's grain output has increased 70 percent but chemical fertilizer use has increased 270 percent.

"We've reached the apex of agricultural emissions of ammonia," Wang said. "Grain production has hit its upper limit, and so the quantity of chemical fertilizers employed should also have reached a maximum level."

"The new focus now is to control industrial emissions of ammonia," said Wang.

Misunderstood Gas

Why is China only now getting around to controlling ammonia emissions? Some experts blame a lack of scientific data.

Some Chinese research institutes began studying components of PM 2.5-type pollution in the 1980s.

"Anyone who studies PM 2.5 pays attention to ammonia," said Song. "Most researchers know the role ammonia plays in PM 2.5 because it is the only alkaline gas in the atmosphere."

Atmospheric science researchers are already familiar with the relationship between ammonia and PM 2.5 pollution. But studies on ammonia emission sources have been inadequate.

"The sources of ammonia are complex," said Zhu Tong, a professor at Peking University's College of Environmental Sciences and Engineering. "At present, we understand relatively little about the sources of ammonia gas in cities."

Wang said that when he started studying PM 2.5 around 2001, he had little knowledge of its chemical components.

He learned more in 2008 in the run-up to that year's Summer Olympics in Beijing. Wang served as chief scientist to the Beijing Atmospheric Environment Joint Monitoring Program, which was aimed at improving air quality monitoring in the Beijing area for the games.

"Considerations brought about by the 2008 Olympics were not only limited to establishing air quality standards, but also how to reduce the sources of pollution," Wang said. "After 2009, we started paying attention to chemical components. At that point, we discovered that the density of ammonia was consistently high."

Yang Fumo, director of CAS' Chongqing Institute of Green and Intelligent Technology, said that sulfur oxide's effects on air pollution were studied long ago and subsequently included in the government's list of emissions slated for mandatory reductions. More recently, government officials have grown aware of nitrogen oxides and have taken steps to control them.

"Ammonia—its quantity and its emission sources—this among the three major pollutants is the one that we know least about," said Yang.

The first step toward knowing more about ammonia emissions, Song said, involves revising the national emissions inventory with new data. CAS, Peking University, Tsinghua University, China Agricultural University, and other institutions have in recent years studied how to revise ammonia emissions data.

But this is no easy task, since getting accurate information from farms and factories can be difficult. Researchers also have to confront skeptics who question their data-gathering methods and results.

Researchers are generally required to make calculations based on the government's statistics-compiling bureaus. And some say firm data from farms can be hard to obtain, since a lot of livestock is raised by small farmers. Data-gathering itself has drawbacks.

"In China, statistics are reported upward through several layers of administrative channels," said Peng. "In this process, it's hard to avoid situations in which there are inaccuracies. There are even problems with under-reporting and cover-ups."

Moreover, he said, because "backyard husbandry is the norm" in the countryside "it is rather difficult to ascertain the quantity of ammonia released" by livestock farmers.

To fully understand how ammonia affects China's air quality, officials say, officials from several government agencies including the ministries of agriculture and environment will have to cooperate.

Some researchers are concerned that the environment ministry plans to control ammonia emissions on farms and livestock facilities that the agriculture ministry oversees. Bringing together these agencies of various stripes, however, are the scientists.

"We have reached the stage where scientists make suggestions to the state," said Wang.