The latest research conducted by the Chinese Academy of Sciences found a large amount of nitrogen-containing organic compounds in the recent smog and haze in Beijing, Tianjin and Hebei province.

Such compounds are the key components of the photochemical smog, in which the compounds react with sunlight and produce airborne particles and ground-level ozone, both of which are potentially harmful, Wang Yuesi, the leader of the research, told China Youth Daily.

Photochemical smog shrouded Los Angeles during the 1940s and 1950s, resulting in hundreds of premature deaths and 2,000 traffic accidents in a single day in 1954.