Little evidence currently exists on the effects of COVID-19 lockdowns on air quality in low-income countries, where most air pollution-linked deaths occur. We offer the first study on the lockdown impacts in Vietnam, a poorer country with worsening air pollution that has had a successful fight against early waves of the pandemic. We compile a new, rich database from various sources including satellite air pollution data for the past year from January 2020 to January 2021 that covers both the pre-pandemic and post-pandemic lockdown periods. Employing the Regression Discontinuity Design method, we find NO2 concentration to decrease by 24 to 32 percent two weeks after the COVID-19 lockdown. While these positive effects on air quality are comparable to those found in previous studies on stricter gasoline regulations or transition to cleaner energy sources, they dissipate after ten weeks. Our findings are robust to different measures of air quality and model specifications. We also find that mobility restrictions are a potential channel for improved air quality. Finally, our back-of-the envelope calculations suggest that two weeks after the lockdown, the economic gains from better air quality are at least $33.9 million US dollars.