In a poorly ventilated indoor environment, it is less likely that plumes of contaminated air will be dispersed quickly away from occupants in the same way they would outdoor. When we are outside, we are less at risk because the outside dilutes the plumes of pathogens. This is why it is vital to dilute a respiratory virus, including the Covid-19 virus in indoor air. A growing body of evidence supports this, such as this such as this report from Rehva which explains clearly how Covid-19 is air borne pathogen and that diluting the pathogen inside reduces risks.