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　　Off-road mobile machinery has a wide range of applications, including construction machinery, agricultural machinery, garden machinery, generator sets, fishery machinery and airport ground handling equipment, among which construction machinery and agricultural machinery account for the highest proportion. China Mobile Source Environmental Management Annual Report shows that in 2020, the NOx and PM emissions of these two types of machinery will reach 3.166 million tons and 168,000 tons respectively, accounting for 28% and 55% of the total emissions of mobile sources. In order to implement the Law on the Prevention and Control of Air Pollution and further strengthen the pollution prevention and control of off-road mobile machinery, in 2014, the Ministry issued the Emission Limits and Measurement Methods of Diesel Engine Exhaust Pollutants for Off-road Mobile Machinery (Phase III and IV in China) (GB 20891—2014), requiring the implementation of the third-stage emission standards on October 1, 2015. In January, 2021, based on the needs of environmental management and the situation of the industry, the Ministry revised and improved the technical requirements and implementation time of the fourth stage, and jointly issued a revised version of the fourth stage emission standards (hereinafter referred to as the National Four Standards) by the General Administration of Market Supervision, requiring the implementation of the National Four Standards on December 1, 2022.