**5. Conclusions**

The pandemic has likely changed our relationship with green space, which has numerous established public health and societal benefits, and the nature of this change is not fully understood. Scientific evidence is needed regarding travel to green space, an important environmental determinant of human health, under normal conditions and pandemics. We investigated the effect of green space on human mobility patterns during the COVID-19 pandemic using large-scale mobility data from social media; our findings imply potential increases in usage of green space in Maryland and California, USA, particularly parks and environment for recreational activities when other essential social activities were prohibited or discouraged due to the control measures of COVID-19. Results suggest that understanding environmental factors associated with mobility changes during a pandemic can aid decision-makers with preparing preventive measures against public health burdens caused by pandemics. We urge future studies to explore these findings, expand relevant data sources, investigate methodologies to estimate the health benefits of green space impeded by a pandemic and the most vulnerable persons to such damages.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2071-1050/12/22/9401/s1, Figure S1: Histograms of the statistics of the daily percent changes in mobility in Maryland, Figure S2: Histograms of the statistics of the daily percent changes in mobility in California, Figure S3: Trend in the distance traveled by users during the study period, Figure S4: Pair-wise scatter plots for EVI and covariates in Maryland, Figure S5: Pair-wise scatter plots for EVI and covariates in California, Table S1: Regression coefficients of covariates in the statistical models including parks (all types), EVI, retail and hospitals, population density, and percent impervious area.

**Author Contributions:** Conceptualization, S.H.; methodology, S.H.; software, S.H.; validation, S.H. and M.L.B.; formal analysis, S.H.; investigation, S.H.; resources, S.H.; data curation, S.H.; writing—original draft preparation, S.H. and C.C.L.; writing—review and editing, S.H. and M.L.B.; visualization, S.H. and M.L.B.; supervision, M.L.B.; project administration, M.L.B.; funding acquisition, M.L.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the U.S. Environmental Protection Agency, grant number RD835871.

**Acknowledgments:** This publication was developed under Assistance Agreement No. RD835871 awarded by the U.S. Environmental Protection Agency to Yale University. It has not been formally reviewed by EPA. EPA does not endorse any products or commercial services mentioned in this publication. The content is solely the responsibility of the authors and does not necessarily represent the official views of the EPA. Authors appreciate Facebook for providing Facebook Disease Prevention Maps (https://dataforgood.fb.com/tools/disease-prevention-maps/).

**Conflicts of Interest:** The authors declare no conflict of interest.
