Adding to the direct effect of reducing sunlight are indirect effects, such as aerosol-induced cloud cover and increased reflectivity, which further reduce the sunlight reaching plants. Finally, harm from growth-stunting ozone, acid deposition and other air pollutants also worsens the impact of poor air quality. There are many potential sources for the haze. The coal China uses to fire much of its industry produces soot and fine particles. Fuel for cooking and home heating also tends to be dirty.
Agricultural practices involve burning crop debris at the end of the growing season.
And China gets hit each spring with dust from desert regions in the western part of the country. The study was done by a consortium of groups that included the Chinese Academy of Meteorological Sciences, the U.S. National Center for Atmospheric Research and the Abdus Salam International Centre for Theoretical Physics in Italy in addition to Georgia Tech.