# Evaluation of Light Pollution in Global Protected Areas from 1992 to 2018
## 6 Conclusions  
In this study, we developed a framework to evaluate the light pollution in global PAs using WDPA and globally harmonized NTL data over the past decades (1992 to 2018). We identified three categories of light pollution (i.e., 5974 non-polluted, 8141 continuously polluted, and 16,509 discontinuously polluted) in PA and investigated the global distribution of these PAs. Then, we analyzed the temporal trend of NTL in polluted (i.e., the continuously and discontinuously polluted) PAs. Specifically, NTL trends in the first polluted interval and high-intensity intervals were analyzed with consideration of protection policies and urbanization.  
Those PAs affected by NTL are mainly distributed in regions with latitudes from 30\({}^{\circ}\)N to 60\({}^{\circ}\)N, representing three key regions (i.e., Europe, the USA, and East Asia). Overall, because of global urbanization, the temporal trend of NTL in global PAs is increasing, except for the USA and Japan, showing a slightly decreasing trend. This is probably related to socioeconomic and demographic factors. Most PAs are close to lit pixels when regarding their distances to the first or the high-intensity polluted buffers (i.e., less than 10 km), especially for the PA types of habitat/species management area (IV) and protected landscape/seascape (V). These PAs are more likely to be affected by light pollution than other regions under future global urbanization scenarios.  
Characterizing the spatial relationship between PAs and NTL and the trend of NTL intensity in/around PAs is of high importance for biodiversity conservation. Our study provides a global perspective on light pollution in worldwide PAs and identified different types and hotspots of PAs using temporally consistent NTL time series data. Global urbanization is the main driver raising the risk of light pollution in/around PAs, of which their distance to NTL has become close over the past decades. As a result, more attention is required to mitigate these risks to support sustainable development. It is also worthy to note that the number of PAs in China is not so many in WDPA, although China has experienced prevalent urban sprawl over the past decades [72].  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/article/10.3390/rs13091849/s1](https://www.mdpi.com/article/10.3390/rs13091849/s1)]([https://www.mdpi.com/article/10.3390/rs13091849/s1](https://www.mdpi.com/article/10.3390/rs13091849/s1)). Figure S1: An illustration of continuously polluted category. The case area in Paris (France) (a) and change of nightlights (b). Figure. S2: An illustration of the discontinuously polluted category in Zhangjiajie (China) (a) with NTL dynamics (b) and temporal trend analysis (c). Figure. S3: An illustration of buffers around the protected area in Seattle and the highlighted high-intensity intervals.  
**Author Contributions:** Conceptualization, X.L.; methodology, X.L., and H.M.; software, H.M., Y.W.; validation, X.L., and H.M.; formal analysis, X.L., and H.M.; investigation, H.M.; resources, X.L., X.D., J.H. and W.S.; data curation, X.L.; writing--original draft preparation, H.M.; writing--review and editing, X.L., H.M., Y.W., Y.H., J.H., W.S., T.H., P.Y., F.X., and X.D.; visualization, H.M.; supervision, X.L., J.H., and W.S.; project administration, X.L.; funding acquisition, X.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Chinese University Scientific Fund, grant number 15051001.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Acknowledgments:** We acknowledge the protected planet program for their share of the WDPA dataset. We thank the editors and reviewers for their helpful and constructive comments on our work.  
**Conflicts of Interest:** The authors declare no conflict of interest.