Pedestrians cover their face as they walk along the dusty road in Kathmandu, Nepal February 27, 2017. Nepal has forced 2,500 old vehicles off roads in its capital city of Kathmandu, part of a fight against alarming air pollution levels that have hit nine times World Health Organisation (WHO) limits. Air pollution has been a chronic problem in rapidly growing Kathmandu, which sits in a Himalayan valley and is home to more than 3mn people. (Photo by Navesh Chitrakar/Reuters)

The proliferation of marijuana edibles for both medical and recreational purposes is giving rise to a cottage industry of baked goods, candies, infused oils, cookbooks and classes that promises a slow burn as more states legalize the practice and awareness spreads about the best ways to deliver the drug. Edibles and infused products such as snack bars, olive oils and tinctures popular with medical marijuana users have flourished into a gourmet market of chocolate truffles, whoopie pies and hard candies as Colorado and Washington legalized the recreational use of marijuana in the past year. Photo: In this Thursday, July 10, 2014, photo, Mike Fitzgerald, right, teaches behind a sample display of cannabis-infused products during a cooking class at the New England Grass Roots Institute in Quincy, Mass. (Photo by Michael Dwyer/AP Photo)

A shot of Pu'uo crater, the main source of lava from Kilauea, taken from a helicopter in Kilaura, Hawaii. (Photo by Kirk Aeder/Barcroft Media)

Flames rage through a pile of tires at the tire dump of Sesena in Toledo, Spain, 13 May 2016. The tire dump reportedly contains over 100,000 tons of tires and reaches to the neighbouring town of Valdemoro in Madrid. According to local authorities, the fire was apparently deliberately started as it had been raining till midnight and the fire started early 13 May 2016 at a small spot in Valdemoro. (Photo by Ismael Herrero/EPA)

Two women lighting cigarettes on a tennis court in Essex, England circa 1930's. (Photo by Keystone View/FPG/Getty Images)

A woman takes part in a global March for marijuana in Medellin, Colombia, May 7, 2016. The Global Marijuana March (GMM) is an annual rally held at different locations across the planet. It refers to cannabis-related events that occur on the first Saturday in May, or thereabouts, and may include marches, meetings, rallies, raves, concerts, festivals and information tables. (Photo by Fredy Builes/Reuters)

Bill Moreau watches as the Black Forest fire burns near his house near Black Forest Road Tuesday afternoon, June 11, 2013, near Colorado Springs, Colo. The Black Forest Fire was one of at least three significant wildfires burning in Colorado amid gusty winds and record-breaking hot, dry weather. (Photo by Christian Murdock/AP Photo/The Colorado Springs Gazette)

Workers are pictured at a shisha manufacturing factory in Baghdad December 17, 2014. (Photo by Thaier Al-Sudani/Reuters)