How clean are electric vehicles? Evidence-based review of the effects of electric mobility on air pollutants, greenhouse gas emissions and human healthAtmospheric Environment Journal 185 (2018), 64-77.
AbstractThere is a growing need for a broad overview of the state of knowledge on the environmental aspects of Electric Vehicles (EVs), which could help policymakers in the objective of making road transportation more sustainable and environmental friendly. This study provides a comprehensive review of the effects of EVs adoption on air quality, greenhouse gas emissions, and human health. Specifically, we (i) synthesized relevant published literature related to environmental implication of EVs, (ii) quantitatively evaluated the effect of EVs on environment and human health, and (iii) identified research gaps and recommend future research areas for the adoption of EVs and their benefits to society. We assessed in total 4734 studies and selected 123 articles of more
detailed review, with 65 articles fulfilling the inclusion criteria. The studies reviewed consistently showed reductions in greenhouse gas emissions and emissions of some criteria pollutants. Particularly on PM and SO2, the increases or decreases are very dependent on the context. Overall, the positive benefits of EVs for reducing greenhouse gas emissions and human exposure depends on the following factors: (i) type of EV, (ii) source of energy generation, (iii) driving conditions, (iv) charging patterns, (v) availabilty of charging infrastructure, (vi) government policies, and (vii) climate of a regions. This study provides a comprehensive analysis and review on the benefits of electric mobility.
3.1.2. GHG emissions
Most studies have considered CO2 emissions to link GHGs with electric mobility. From the 65 articles that fulfilled the inclusion criteria, 51 reported results for CO2 emissions. Fig. 8 indicates that EVs are associated with substantial reductions in CO2 emissions. According tothe literature reviewed, CO2 emissions due to EV penetration are less sensitive to the variation of source of energy generation than particulate and gaseous pollutants. In other words, some studies have shown
that even with a high percentage of electricity generated by coal power plants, EVs may still reduce emissions of CO2. For example, in China where the electric grid is mostly dominated by coal generation, BEVs can reduce CO2 emissions by 20%, but increase PM10, PM2.5, NOx, and
SO2 emissions by 360%, 250%, 120%, and 370%, respectively (Huo et al., 2013). However, when we focus on government targets for GHG emissions reduction, studies have reported that EVs can reduce petroleum imports, but it will be challenging for EVs to achieve the government goals for CO2 reduction (Doucette and Mcculloch, 2011; Shen et al., 2014a,b).
Looks like the 20% figure for China is from a single study in 2013. I found two later papers by Huo et. al.
Life-cycle assessment of greenhouse gas and air emissions of electric vehicles: A comparison between China and the U.S.Atmospheric Environment 108 (2015) 107-116
AbstractWe evaluated the fuel-cycle emissions of greenhouse gases (GHGs) and air pollutants (NOx, SO2, PM10 and PM2.5) of electric vehicles (EVs) in China and the United States (U.S.), two of the largest potential markets for EVs in the world. Six of the most economically developed and populated regions in China and the U.S. were selected. The results showed that EV fuel-cycle emissions depend substantially on the carbon intensity and cleanness of the electricity mix, and vary significantly across the regions studied. In those regions with a low share of coal-based electricity (e.g., California), EVs can reduce GHG and air pollutant emissions (except for PM) significantly compared with conventional vehicles. However, in the Chinese regions and selected U.S. Midwestern states where coal dominates in the generation mix, EVs can reduce GHG emissions but increase the total and urban emissions of air pollutants. In 2025, EVs will offer greater reductions in GHG and air pollutant emissions because emissions from power plants will be better controlled; EVs in the Chinese regions examined, however, may still increase SO2 and PM emissions. Reductions of 60e85% in GHGs and air pollutants could be achieved were EVs charged with 80% renewable electricity or the electricity generated from the best available technologies of coal-fired power
plants, which are futuristic power generation scenarios.
The fuel-cycle emissions of EVs depend substantially on the carbon intensity and cleanness of the electricity mix. With an electricity generation as in 2012, EVs running in regions with a
large share of natural gas based electricity and good pollutant control of power plants (as is the case in CA and NPCC) can reduce GHG emissions and the total and urban emissions of air pollutants
(except total PM in CA) compared with conventional gasoline vehicles. However, EVs operating in regions where coal dominates the power mix (Chinese regions and the three U.S. Midwestern states)
could increase both the total and the urban emissions, or offer limited reductions. In 2025, as the share of coal-based electricity decreases and emissions from power plants are controlled further,
EVs could offer greater reductions in GHG and air pollutant emissions, although Chinese regions may still increase SO2 and PM emissions. On the other hand, considering that EVs transfer a significant
proportion of vehicle fuel-cycle emissions from nearground tailpipes in populated cities to high chimneys that are usually far from people, EVs may be able to reduce the urban pollutant concentrations and benefit human health.
Assessment of electrical vehicles as a successful driver for reducing CO2
emissions in ChinaApplied Energy 184 (2016) 995–1003
AbstractThis paper analyses the impacts of the gasoline vehicle replacement programme with EVs at different penetration rates on petroleum and electricity sectors and their CO2 emissions. The study utilises a top-down-type Environmental Input–Output (EI–O) model. Our results show that the replacement of gasoline cars with EVs causes greater impacts on total gasoline production than on total electricity generation. For example, at 5%, 20%, 50%, 70% and 100% gasoline vehicle replacement with EVs, the total gasoline production decreases by 1.66%, 6.65%, 16.62%, 23.27% and 33.24% in policy scenario 1, while the total electricity production only increases by 0.71%, 2.82%, 7.05%, 9.87% and 14.10%. Our study
confirms that the gasoline vehicle replacement with EVs, powered by 80% coal, has no effect on overall emissions. The CO2 emissions reduction in the petroleum sector is offset by the increase in CO2 emissions in the electricity sector, leaving the national CO2 emissions unchanged. By decarbonising the electricity sector, i.e. using 30% less coal in electricity generation mix, the total CO2 emissions will be reduced by 28% (from 10,953 to 7870 Mt CO2) on the national level. The gasoline vehicle replacement programme with EVs, powered by 50% coal-based electricity, helps reduce CO2 emissions in petroleum sector and contributes zero or a very small proportion of additional CO2 emissions to the electricity sector (policy scenario 2 and 3). We argue that EVs can contribute to a reduction of petroleum dependence, air quality improvement and CO2 emission reduction only when their introduction is accompanied by aggressive electricity sector decarbonisation.
7. Conclusion
The purpose of this paper is to examine direct impacts on total gasoline production and electricity generation and their CO2 emissions as a result of gasoline vehicle replacement with EVs in China. We find that the introduction of EVs in China is only sensible if the power sector is decarbonised by using renewable energy sources. As long as power is generated by coal, the vehicle replacement programme has no effect (policy scenario 1). As soon as the electricity sector is decarbonised, EVs contribute zero or a very small amount of additional CO2 emissions to the electricity sector (policy scenario2 and 3). Our study shows that EVs are able to reduce dependency on petroleum and to improve air quality, however, they are not the main driver for reducing the national CO2 emissions in China. Policies on structural changes in primary economic sectors, i.e. improvement of carbon intensity in the electricity sector, are needed to achieve a substantial reduction of national CO2 emissions before any new products, such as EVs, can be rolled out in the transportation sector in the future. Currently, renewable and low-carbon energy sources are still under-used and the electricity sector is largely powered by coal in China [75,76]. It is therefore an ineffective and counterproductive activity for Chinese Government to promote EVs.
The last sentence states it very clearly, unless the Chinese electricity supply is significantly decarbonized, EV's will not reduce GHG emissions. For other countries, with much less fossil fuels in their electricity supply, EV's will significantly reduce GHG emissions. Unfortunately, China is decarbonizing at a very slow rate (there was a burst of activity in the past couple of years but the growth rate has been greatly reduced due to government policy changes). What EVs will do is greatly increase Chinese energy security as they shift demand from imported oil to domestically produced coal. This makes great sense given the increasingly competitive relationship with the US and the easily interdictable (and easily affected by sanctions) nature of oil tankers travelling through the Straits of Malacca.