The outbreak of the Covid-19 epidemic has had a significant impact on the mode of production and life worldwide. For example, all provinces and cities in China initiated a first-level response mechanism to protect public health. The resulting changes in travel activities have produced significant environmental pollutant emission reduction effects. Based on daily air pollution data from 74 major Chinese cities that first implemented the new air quality standards in China, this paper uses the regression discontinuity method to identify the impact of the first-level response policy on urban air pollution and has shown that cities' average air quality index and PM2.5 has dropped by 10% and 16% under the first-level response policy. The results are still consistent through the robustness test and the placebo test. This unique natural experiment allows a better understanding of the contributions of the transportation sector to air pollution problems in China. It also allows for an improved understanding of the sources of air pollution that are most responsive to transportation changes and the differential responses in different geographic locations across the country.