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On April 20, 2017, at 4:20 in the afternoon, 15 000 people in San Francisco’s Golden Gate Park lit marijuana joints during the annual “420 Day.” In cannabis culture, April 20 has become an international countercultural holiday; people gather to celebrate and consume cannabis, typically around 4:20 pm.
The giant cloud of secondhand marijuana smoke was visible from the University of California, San Francisco, half a mile away. The cloud embodied the revelers’ new freedom on this first 420 Day since California voters legalized recreational marijuana in November 2016. The smoke cloud, however, was also part of a growing source of air pollution.
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Corresponding Author: Stanton A. Glantz, PhD, Center for Tobacco Control Research and Education, 530 Parnassus Ste 366, University of California, San Francisco, San Francisco, CA 94143-1390 (Stanton.Glantz@ucsf.edu).
Published Online: November 20, 2017. doi:10.1001/jamainternmed.2017.5301
Conflict of Interest Disclosures: None reported.
Funding/Support: This work was funded in part by the National Institute of Drug Abuse (grant No. R01DA043950 to Dr Glantz and grant No. R21DA031966 to Dr Springer), the California Tobacco Related Disease Research Program (grant No. 25IR-0030 to Dr Springer) and the Elfenworks Foundation.
Role of the Funder/Sponsor: The funder/sponsors had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
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