Haze over China
Dense smog settled over the North China Plain on February 20, 2011. The featureless gray-brown haze is so thick that the ground is not visible in parts of this photo-like image taken at 11:35 a.m. by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. At that time, a weather station at Beijing’s airport reported visibility of 1.9 miles (3.1 kilometers). Visibility dropped as low as 1.1 miles (1.8 km) later in the afternoon. Smog frequently builds up in eastern China during the winter when weather conditions trap pollutants over the plain. Haze had been reported over Beijing for much of the previous week. It is not possible to tell from this view exactly what pollutants made up the haze on February 20, but it probably contains mostly soot or black carbon and possibly some ground-level ozone. Soot is released from burning fossil fuels (particularly diesel and coal), wood, and other biofuels. These same processes also release chemicals that combine in sunlight to form ozone: methane, nitrogen oxides, volatile organic compounds, and carbon monoxide. In China, coal is an important fuel burned in home heating and cooking and energy production.