Emission　benefits　of　transit　buses　depend　on　ridership.　Declines　in　ridership　caused　by　COVID-19　leads　uncertainty　about　the　emission　reduction　capacity　of　buses.　This　paper　provides　a　method　framework　for　analyzing　spatio-temporal　emission　patterns　of　buses　in　combination　with　real-time　ridership　and　potential　emission　changes　in　the　post-COVID-19　future.　Based　on　GPS　trajectory　and　Smart　Card　data　of　2056　buses　from　278　routes　covering　1.5　million　ridership　in　Qingdao,　China,　spatio-temporal　emissions　characteristics　of　buses　are　studied.　7589　taxis　with　0.2　million　passengers＇　trips　are　used　for　acquiring　private　cars＇　emissions　to　evaluate　the　emissions　difference　between　buses　and　cars.　Empirical　results　show　that　the　average　difference　between　buses　and　cars　with　2　persons　can　reach　up　to　117　g/km-person　during　7:00-8:59　and　115　g/km-person　during　17:00-18:59.　However,　buses　have　various　emission　benefits　around　the　city　at　different　periods.　A　double　increase　in　emissions　during　non-rush　hours　can　be　observed　compared　with　rush　hours.　224　online　survey　data　are　used　to　study　the　potential　ridership　reduction　trend　in　post-COVID-19.　Results　show　that　56.3%　of　respondents　would　decrease　the　usage　of　buses　in　the　post-COVID-19　future.　Based　on　this　figure,　our　analysis　shows　that　per　kilometer-person　emissions　of　buses　are　higher　than　cars　during　non-rush　hours,　however,　still　lower　than　cars　during　rush　hours.　We　conclude　that　when　ridership　reduces　by　more　than　40%,　buses　cannot　be　＂greener＂　travel　modal　than　cars　as　before.　Finally,　several　feasible　policies　are　suggested　for　this　potential　challenge.　Our　study　provides　convincing　evidence　for　understanding　the　emission　patterns　of　buses,　to　support　better　buses　investment　decisions　and　promotion　on　eco-friendly　public　transport　service　in　the　post-COVID-19　future.