Outdoor transmission may represent fewer than one in 1000 Covid-19 cases. A database of more than 2000 international superspreader events found only one that happened exclusively outdoors.

Researchers examining the beginning of the outbreak in China looked at more than 7000 infections and found only one case of outdoor transmission. Strangely enough, few superspreader events have happened on aeroplanes or in gyms, likely due to better ventilation.

Source: What we've learned about the virus over 18 months in the wilderness