The document discusses the results of a study on the impact of COVID-19 lockdowns on air pollution. Researchers analyzed data from dozens of countries and found that lockdowns led to an average decline of nearly 30% in nitrogen dioxide levels over cities. However, they also observed that this improvement was temporary and air pollution rebounded once lockdowns were lifted as vehicle traffic increased again. The short-term reductions are not enough to meet long-term air quality and climate targets according to the researchers.