The coronavirus (COVID-19) pandemic and attendant lockdown measures present serious threats to emotional well-being worldwide. Here, we examined the extent to which being outdoors (vs. indoors), the experience of loneliness, and screen-time are associated with emotional well-being during the COVID-19 pandemic using an experiencing sampling method. In April 2020, Austrian adults (N = 286, age M = 31.0 years) completed a 21-day experience sampling phase in which they reported their emotional well-being (i.e., happiness), whether they were indoors or outdoors, and loneliness at three random time-points each day, as well as their daily screen-time. Results indicated that being outdoors was associated with higher emotional well-being, whereas greater loneliness and greater daily screen-time were associated with poorer well-being. Additionally, the impact of loneliness on well-being was weaker when participants were outdoors than indoors. These results have health policy implications for the promotion of population well-being during pandemics.