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.
Glantz SA, Halpern-Felsher B, Springer ML. Marijuana, Secondhand Smoke, and Social Acceptability. JAMA Intern Med. 2018;178(1):13–14. doi:10.1001/jamainternmed.2017.5301
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