A spike in Chinese air pollution over the last three decades has caused a 60 percent increase in the levels of nitrogen pollutants that ultimately end up back on the nation’s land and in its water, a new study has found. In an analysis of 270 monitoring sites across the country, researchers found that the annual deposition of nitrogen, as measured in precipitation, had increased from 13.2 kilograms per hectare in 1980 to about 21.1 kilograms per hectare in 2010. Scientists say so-called nitrogen deposition occurs when nitrogen in the atmosphere is washed back to the planet’s surface by rain and snow in the form of pollutants such as nitrates and ammonium. Elevated nitrogen levels can trigger harmful ecological effects, from soil acidification to feeding algae blooms. According to the study, published in Nature, leaves of herbaceous and woody plants absorbed 33 percent more nitrogen in 2010 than in 1980, while rice, wheat, and maize crops on unfertilized fields had a 16 percent increase. The spike in pollution levels has been driven by an increase in industrial emissions, agricultural uses, and transportation.