The large (26-fold over the past 25years) increase in the on-road vehicle fleet in China has raised sustainability concerns regarding air pollution prevention, energy conservation, and climate change mitigation. China has established integrated emission control policies and measures since the 1990s, including implementation of emission standards for new vehicles, inspection and maintenance programs for in-use vehicles, improvement in fuel quality, promotion of sustainable transportation and alternative fuel vehicles, and traffic management programs. As a result, emissions of major air pollutants from on-road vehicles in China have peaked and are now declining despite increasing vehicle population. As might be expected, progress in addressing vehicle emissions has not always been smooth and challenges such as the lack of low sulfur fuels, frauds over production conformity and in-use inspection tests, and unreliable retrofit programs have been encountered. Considering the high emission density from vehicles in East China, enhanced vehicle, fuel and transportation strategies will be required to address vehicle emissions in China. We project the total vehicle population in China to reach 400-500 million by 2030. Serious air pollution problems in many cities of China, in particular high ambient PM concentration, have led to pressure to accelerate the progress on vehicle emission reduction. A notable example is the draft China 6 emission standard released in May 2016, which contains more stringent emission limits than those in the Euro 6 regulations, and adds a real world emission testing protocol and a 48-h evaporation testing procedure including diurnal and hot soak emissions. A scenario (PC[1]) considered in this study suggests that increasingly stringent standards for vehicle emissions could mitigate total vehicle emissions of HC, CO, NO and PM in 2030 by approximately 39%, 57%, 59% and 79%, respectively, compared with 2013 levels. With additional actions to control the future light-duty passenger vehicle population growth and use, and introduce alternative fuels and new energy vehicles, the China total vehicle emissions of HC, CO, NO and PM in 2030 could be reduced by approximately 57%, 71%, 67% and 84%, respectively, (the PC[2] scenario) relative to 2013. This paper provides detailed policy roadmaps and technical options related to these future emission reductions for governmental stakeholders.

The formation mechanism of aerosol sulfate during wintertime haze events in China is still largely unknown. As companions, SO2 and transition metals are mainly emitted from coal combustion. Here, we argue that the transition metal-catalyzed oxidation of SO2 on aerosol surfaces could be the dominant sulfate formation pathway and investigate this hypothesis by integrating chamber experiments, numerical simulations and in-field observations. Our analysis shows that the contribution of the manganese-catalyzed oxidation of SO2 on aerosol surfaces is approximately one to two orders of magnitude larger than previously known routes, and contributes 69.2% ± 5.0% of the particulate sulfur production during haze events. This formation pathway could explain the missing source of sulfate and improve the understanding of atmospheric chemistry and climate change.

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Abstract. China's new "Twelfth Five-Year Plan" set a target for total NO x emission reduction of 10 % for the period of 2011-2015. Heavy-duty diesel vehicles (HDDVs) have been considered a major contributor to NO x emissions in China. Beijing initiated a comprehensive vehicle test program in 2008. This program included a sub-task for measuring onroad emission profiles of hundreds of HDDVs using portable emission measurement systems (PEMS). The major finding is that neither the on-road distance-specific (g km −1 ) nor brake-specific (g kWh −1 ) NO x emission factors for diesel buses and heavy-duty diesel trucks improved in most cases as emission standards became more stringent. For example, the average NO x emission factors for Euro II, Euro III and Euro IV buses are 11.3 ± 3.3 g km −1 , 12.5 ± 1.3 g km −1 , and 11.8 ± 2.0 g km −1 , respectively. No statistically significant difference in NO x emission factors was observed between Euro II and III buses. Even for Euro IV buses equipped with SCR systems, the NO x emission factors are similar to Euro III buses. The data regarding real-time engine performance of Euro IV buses suggest the engine certification cycles did not reflect their real-world operating conditions. These new on-road test results indicate that previous estimates of total NO x emissions for HDDV fleet may be significantly underestimated. The new estimate in total NO x emissions for the Beijing HDDV fleet in 2009 is 37.0 Gg, an increase of 45 % compared to the previous study. Further, we estimate that the total NO x emissions for the na-