@PoppaGeorgio5 @ems_jn 20 air exchanges is good, but not sufficient to prevent accumulation of risk of mostly near-field transmission (i.e. someone breathing directly on you before the air is exchanged or filtered) over time. See article linked in other reply.
@PoppaGeorgio5@ems_jn 20空气交换是好的，但不足以防止随着时间的推移，主要是近场传播的风险积累（即在交换或过滤空气之前有人直接在你身上呼吸）。见其他回复中链接的文章。