The greenhouse gas and reactive nitrogen mitigation from the Japanese passenger car fleet

【背景・経緯】
　To achieve sustainable mobility, great efforts have been made in the transportation sector such as promoting next generation cars including hybrid vehicles (HVs), battery electric vehicles (BEVs), and fuel cell vehicles (FCVs). Policies tackling target environmental impacts can affect different aspects of environmental quality adversely or beneficially, which brings about questions on trade-offs or co-benefits. The passenger car fleet contributes an important part of total emissions driving concerns on both climate change and nitrogen cycle disturbance. In this study, we investigated simultaneously the time series greenhouse gas and reactive nitrogen emissions of the Japanese passenger car fleet from a life cycle perspective. The integrated model which consists of the dynamic material flow sub-model and life cycle analysis sub-model was developed for the analysis.

 

【成果】
　The evolving car stock composition leads to significant transition of the energy consumption structure and subsequent emission characteristics. The greenhouse gas emission of passenger cars was about 120.4 million t CO₂-e in 2000. It was predicted to be 74.7 million t CO₂-e in 2030, as shown in Fig. 1. The emission of reactive nitrogen was 152.7 kt Nr in 2000 and decreased to 36.0 kt Nr in 2030. Compared with carbon emission, several different features were observed for nitrogen emission. First, a sharp decline was observed for the total reactive nitrogen emission from 2000 to 2010. And then the decline slowed down significantly. Second, reactive nitrogen emission increases were not observed across all categories of cars from 2000 to 2030. Third, the reactive nitrogen emission from Tank to Wheel (TTW) stage was higher than that from Well to Tank (WTT) stage from 2000 to 2013, whereas WTT emission exceeded the TTW emission from 2013 to 2030. The time series results indicated that the contribution of key pollutant species is also different in different periods, which calls for a timely policy adjustment to increase its effectiveness.

 

Figure 1. Emissions of greenhouse gases and reactive nitrogen from 2000 to 2030 by powertrain category, size, and life cycle stage.

 

【成果の意義・今後の展開】
　Investigation on car fleet emissions is capable of reflecting the dynamic penetration of next generation cars and analyzing the holistic policy implications. Examining the mitigations of greenhouse gas and reactive nitrogen simultaneously can provide new insights that can’t be revealed by investigating one at a time. On the other hand, one snapshot of emission in one year could not provide tendency information. Dynamic emission modeling is thus essential. This study explored the time series mitigation profiles of greenhouse gas and reactive nitrogen, shedding new lights on contributions to climate action and the sustainable nitrogen management declaration.

2023年09月07日