Global lockdowns in 2020 reduced pollutants such as carbon dioxide and nitrogen oxides by between 10 and 30 percent. However, this temporary behaviour change is unlikely to result in long term impact. Under pessimistic assumptions that travel restrictions continue until the end of 2021, this temporary behaviour change would only prevent 0.01° C of warming by 2030.
(https://bit.ly/3lie3j0, https://go.nature.com/3lj1VxZ)