Driving reactive nitrogen emissions in China: Competition between scale and efficiency

Reactive nitrogen (Nr) emissions aggravate air and water pollution across the world. The factors influencing Nr emissions have not been clearly uncovered, especially for regions under rapid economic growth. Here we modeled total Nr emissions in mainland China and analyzed factors driving their growth during the decade (2000-2010) of fastest socioeconomic development. Results show that total Nr emissions increased from 24.9 terrogram (Tg) to 35.2 Tg, a 41.7% increase with an average annual growth rate of 3.5%. Agricultural activities, including crop planting and livestock and poultry breeding, together took a substantial but decreasing share, from 75.2% in 2000 to 61.4% in 2010. Industrial wastewater discharge, energy use, and crop production are the three largest sources contributing to the Nr emissions growth. Factors related to scale (e.g., the amount of industrial energy use) led to a growth in Nr emissions, and factors related to efficiency (e.g., industrial energy use per unit of economic output) contributed to reduction. The decreasing effect of efficiency gains, however, was still unable to overcome the increasing effect of the activity scale. More in-depth research studies on mitigation strategies are required, to inform the decoupling between socioeconomic development and Nr emissions.