The Applications of ‘N Offset’ Mechanism in the Evaluation of Reactive Nitrogen Emissions Reduction in a Typical China’s Urban Agglomeration

The rapid development of urbanization, resulting in direct and indirect emissions of anthropogenic reactive nitrogen to environment during nitrogen consumption, had brought the huge ecological pressure and serious environmentally pollution. Took a typical China’s urban agglomeration (Beijing-Tianjin-Hebei agglomeration) as example, this study constructed quantitative analysis of reactive nitrogen emissions and an evaluation index for annual reactive nitrogen removal efficiency of this region by employing data envelopment analysis. After that, this study attempted to put forward reactive nitrogen reduction countermeasures based on ‘N offset’ mechanism for the collaborative development. The results showed that, during urbanization from 2004-2014, the total reactive nitrogen emissions by Beijing-Tianjin-Hebei agglomeration presented slightly decreased with fluctuation. Hebei province was the main contributor to nitrogen emission, occupying 79-84% and 74-79% of nitrogen loss to atmosphere and hydrosphere. The main sources of regional emissions were agricultural activities primarily, and then turned to industrial activities and residential livelihood. The differences existed in the impacts of urbanization on reactive nitrogen emission intensity of each region. The annual emission intensity of this agglomeration was 5.8 t N/km2. Beijing city owned the highest of emission reduction efficiency. The reduction in the emissions intensity of Hebei province and the improvement in emission reduction efficiency of Tianjin city were supposed to be the keys for overall low-nitrogen urbanization within agglomeration. The nitrogen-reduction countermeasures accompanied by corresponding pecuniary compensation, basing on collaborative ‘N offset’ mechanism, would contribute to the reciprocity among Beijing-Tianjin-Hebei agglomeration towards sustainable development.