On October 27, 2014 (September 4 of the 2014 lunar calendar), China, the top ten cities with the worst air conditions in the world, did not make the list. On October 27, 2014, according to the latest "2014 Urban Outdoor Air Pollution Database" released by the World Health Organization. New Delhi, the capital of India, has the highest annual average of 153 for PM2.5. India accounts for half of the 20 cities with the highest PM2.5 values. Among the 20 cities, no China city is on the list. Although in China, many cities are shrouded in gray fog, millions of residents wear masks to go out. On January 20, 2014 local time, New Delhi, India, was shrouded in smog, and the entire city seemed to be covered under a thick gray blanket. The WHO ranks China as the top 20 cities in the world with the highest annual average of PM2.5. One of the murderers of smog is burning straw. In India, one of the reasons why New Delhi has become a city with the worst air in the world is Fireworks set off to celebrate festivals. The World Health Organization (WHO)"2014 Urban Outdoor Air Pollution Database" shows that half of the 20 cities with the highest annual average PM2.5 concentrations in the world come from India, but this data is currently only updated to May 2014. Celebrating Diwali, PM2.5 concentrations surge in New Delhi The Diwali Festival is an important Hindu festival. In order to welcome Diwali, every household in India lights candles or oil lamps, and fireworks illuminate the dark night. According to Agence France-Presse reported on October 26, just after Diwali in India, which is to "celebrate the victory of justice over evil and light repels darkness", PM2.5 data in New Delhi soared to above 250 for the first time, which is the safe concentration set by the WHO. 10 times the upper limit of 25. Agence France-Presse reported that since the annual setting off of fireworks and firecrackers causes casualties and the pungent smoke makes people in the capital breathless, Indian authorities often guide the public to restrict them from setting off fireworks and firecrackers. However, judging from previous years 'values, the surge in PM2.5 concentrations caused by Diwali is only a prelude. Data released by the Central Pollution Control Commission of India show that from November 2013 to January 2014, the average PM2.5 concentration in New Delhi reached 575, while the average PM2.5 concentration in Beijing during the same period was 400. According to CNN, an average of 1400 vehicles are added to the streets of New Delhi every day, and Indian manufacturers only equip them with the most basic emission reduction devices. Smoke from burning garbage, industrial emissions and pollutants from coal-fired power stations also continue to pollute the atmosphere. Medical research shows that toxic smoke can cause residents in New Delhi to develop acute lung epidemics, eye diseases and rickets caused by vitamin D deficiency. Indian Prime Minister Narendra Modi launched the "Clean India Mission" in February 2014, calling on all Indians to take action to control environmental pollution. However, according to CNN's report on May 8, the Indian Center for Science and Environment believes that New Delhi's implementation measures to control pollution are still very "weak." The WHO "2014 Urban Outdoor Air Pollution Database" ranking of the top 10 cities with the worst air in China's "2014 Urban Outdoor Air Pollution Database" shows that New Delhi, the capital of India, has the highest annual average of PM2.5, at 153. Patna, another Indian city, followed closely with a figure of 149. India accounts for half of the 20 cities with the highest PM2.5 values in the WHO data, while the rest come from countries such as Pakistan and Iran. The database includes online public data from 1600 cities in 91 countries around the world, covering the period 2008 - 2013. CNN reported that among the 20 cities, not a single China city was on the list. Although in China, many cities are shrouded in gray fog, millions of residents wear masks to go out. In the database, the highest ranked city is Lanzhou, ranking 36th, with an average annual PM2.5 concentration of 71. Beijing's annual average PM2.5 concentration is 56, ranking 76th. The data source for China is CleanAirAsia, a non-profit organization jointly sponsored by the Asian Development Bank (ADB), the World Bank (WB) and the U.S. Agency for International Development (USAID).