A girl wearing a respirator mask in Beijing, with the Forbidden City in the background.
Beijing experienced 2,589 deaths and a loss of US$328 million in 2012 because of PM2.5 pollution. Cities in China’s Yangtze River Delta, Pearl River Delta, and Beijing-Tianjin-Hebei region suffered over 100 hazy days a year with PM2.5 concentration two to four times above World Health Organization guidelines. Particles less than 2.5 micrometers in diameter, PM2.5, are called "fine" particles and can lodge deeply into the lungs.