A Chinese woman wears a mask to protect from particles blown in during a sandstorm as she walks in the street on May 4, 2017 in Beijing, China. Sandstorms are common in northern China during the spring season and are caused when heavy winds from Mongolia in the north brings sand and pollutants that can blanket Chinese cities and cause air quality to deteriorate. (Photo by Kevin Frayer/Getty Images)

A Palestinian protester sets fire to himself as he throws a molotov cocktail during clashes with the members of the Israeli armed forces in the West Bank city of Hebron, 13 October 2015. The past 12 days have seen the worst spell of street violence in Israel and the Palestinian areas in years, stirred in part by Muslim anger over perceived changes to the status quo observed at a disputed Jerusalem holy site. Sixteen Palestinians from the West Bank and Jerusalem have been killed, but more than half of them have been attackers shot dead after or during attempts to stab Israelis. (Photo by Abed Al Hashlamoun/EPA)

Riot policemen stand in formation during street protests against the decision made by Burundi's ruling National Council for the Defence of Democracy-Forces for the Defence of Democracy (CNDD-FDD) party to allow President Pierre Nkurunziza to run for a third five-year term in office, in the capital Bujumbura, April 26, 2015. Police in the Burundian capital used water cannon and tear gas on Sunday to disperse protesters demonstrating against Nkurunziza seeking a third term, witnesses said, after the government banned protests for or against the move. (Photo by Thomas Mukoya/Reuters)

Flying pigeons pass over Nepalese street vendors near the earthquake damaged UNESCO World Heritage Site, Durbar Square in Kathmandu on May 20, 2015. Nearly 8,500 people have now been confirmed dead in the disaster, which destroyed more than half a million homes and left huge numbers of people without shelter with just weeks to go until the monsoon rains. (Photo by Ishara S. Kodikara/AFP Photo)

Revellers participate in a parade on the street during a carnival in the village of Vevcani, south of Skopje, Macedonia January 13, 2016. Vevcani village marks the annual Orthodox St. Vasilij Day with a carnival that features a 1,400-year-old celebration with pagan roots. The highlights of the carnival include a political satire where masked villagers act out current events. (Photo by Ognen Teofilovski/Reuters)

Joaldunaks return in a trailer to their town at the end of Carnival between of the Pyrenees villages of Ituren and Zubieta, northern Spain, Monday, February 1, 2016. In one of the most ancient carnivals in Europe, dating from before the Roman empire, companies of Joaldunak (cowbells) made up of residents of two towns, Ituren and Zubieta, parade the streets costumed in sandals, lace petticoats, sheepskins around the waist and shoulders, coloured neckerchiefs, conical caps with ribbons and a hyssop of horsehair in their right hands and cowbells hung across their lower back. (Photo by Alvaro Barrientos/AP Photo)

In a July 14, 1967 file photo, left, National Guardsmen make their way along Market Street in Newark, N.J, after an evening of deadly rioting and looting in what came to be known as the Newark riots. In a June 16, 2017 photo, right, an ambulance drives on the same block 50 years later. (Photo by AP Photo/File, left; Julio Cortez, right)

A damaged traffic signal is pictured along a street at a residential area flooded by the Kinugawa river, caused by typhoon Etau in Joso, Ibaraki prefecture, Japan, September 11, 2015. Unprecedented rain in Japan unleashed heavy floods on Friday that tore houses from their foundations, uprooted trees and forced more than 100,000 people from their homes. (Photo by Issei Kato/Reuters)