Will high-speed rail improve air quality, or make it worse? We use data of 270 cities in China from 2000 to 2018 to study the impact of high-speed rail (HSR) on air pollution. Based on the difference-in-difference (DID) model, the regression results show that high-speed rail has reduced air pollution. But the results also show geographic differences. In underdeveloped areas, HSR will increase urban air pollution. The main mechanism is that HSR has affected the industrialization level and the entry of polluting enterprises. Especially in underdeveloped cities, HSR will increase industrial output and attract more polluting companies, which is not conducive to environmental governance.

The development of new digital infrastructure enables the construction of intelligent agricultural production systems, enhances agricultural sustainability, and supports the national “dual-carbon” goals. Based on a theoretical analysis and using panel data for 31 Chinese provinces during 2011–2023, this study constructs a two-way fixed-effects model to empirically test the impact of new digital infrastructure on agricultural carbon emissions, and provides insights for differentiating provincial heterogeneity, as well as impact mechanism. The main findings are as follows: (1) New digital infrastructure is negatively correlated with agricultural carbon emissions, and this conclusion holds after a series of robustness and endogeneity tests. (2) Heterogeneity analysis reveals that, by geographic location, new digital infrastructure has a significant carbon reduction effect in eastern provinces but increases emissions in central provinces. By the digital development level, this study highlights the dual importance of digital infrastructure and financial supports. Contrary to those provinces leading in digital infrastructure development, there is a positive correlation in lagging areas. By policy support level, the significant carbon reduction effect is only observed in provinces with advanced digital-inclusive finance support. For green development policy support, it significantly reduces agricultural carbon emissions in pioneer regions but increases emissions in follower regions. (3) Mechanism tests indicate that new digital infrastructure promotes agricultural carbon reduction mainly through scale-economy effects and energy efficiency upgrading effects. Policy implications to improve agricultural digital infrastructure development and accelerate carbon emission reductions are finally suggested.