Research sources: 

1) Closed environments facilitate secondary transmission of coronavirus disease 2019 (COVID-19):

"The odds that a primary case transmitted COVID-19 in a closed environment was 18.7 times greater compared to an open-air environment (95% confidence interval [CI]: 6.0, 57.9)"

https://www.medrxiv.org/content/10.1101/2020.02.28.20029272v2

2) Department of Homeland Security says: 

* Virus lives longer at low humidity and inactivates faster at higher humidity
* Virus lives longer at low temperatures and inactivates faster as temperature increases
* Sunlight destroys the virus quickl

https://www.scribd.com/document/456897616/DHSST#download