Reducing the emission of ammonia — a smelly, colorless gas released from fertilizers and livestock waste — could be a cheaper and effective means of cutting down the hazardous smog choking Chinese cities, new research suggested.

Gu Baojing, the lead author of the study and professor at Zhejiang University in eastern China, said the costs involved in cutting ammonia emissions were nearly 10 times cheaper than scaling down nitrogen oxides emissions, another key air pollutant that many countries, including China, have been trying to tackle. In China, 80% to 90% of the country’s ammonia emissions is associated with the agricultural sector.

The paper underscoring the growing need to curb ammonia emission was published in the journal Science on Thursday.

“The impacts of ammonia (on air pollution) have been long overlooked,” Gu told Sixth Tone. “Most ammonia comes from agricultural regions, so for a long time people didn’t think it affected the urban area. But you know, air flows.”

Ammonia reacts with nitrogen oxides and sulfur dioxide to form PM2.5, the fine aerosol suspended in the air that is harmful to human health. PM2.5 is known to cause a wide range of illnesses — including cardiovascular and respiratory diseases — with 7 million premature deaths attributed to air pollution globally every year, according to the World Health Organization.

Although China’s air quality has significantly improved over the past years, PM2.5 remains the main air pollutant. The Chinese authorities have set emission limits for many gases that contribute to PM2.5 — including nitrogen oxides and sulfur dioxide — but ammonia is still left out from the country’s pollution reduction plan.

Estimates from Gu’s modeling in 1990 showed that ammonia-resulted PM2.5 cost the world 16 million years of life, which is the tally of the number of years people could have lived otherwise. The loss rose to 23 million years of life in 2013, as ammonia levels rose due to the burgeoning agriculture sector even when emissions of other pollutants declined.

For China, Gu’s team hypothesized that the country’s PM2.5 level would have been 43% lower if no ammonia was emitted in 2013 — an unlikely scenario considering ammonia’s natural presence in animal waste and its role in farming.

However, the study’s authors said one way to reduce ammonia emissions was by providing subsidies for farmers to switch to better fertilizers and tools that would help limit emissions by trapping the gas underneath the soil surface. Gu added that a lower protein diet for livestock and better management of their waste could also help minimize the gas.

“So far, China has set no limits on ammonia emissions,” he said. “But we hope the authorities will lay down a goal, at least cutting ammonia emissions by 40% to 50%.”

Editor: Bibek Bhandari.

(Header image: People Visual)