REINING IN BROWN CLOUDS.

The article focuses on the air pollutants called brown clouds. It states that brown clouds contain nitrogen oxides, fly ash, and soot particles that could cause respiratory problems. It mentions that brown clouds affect five areas including East Asia, the Sahara Desert, and eastern Pakistan, and also persist throughout Europe and eastern U.S. It also notes that environmental activists and policy groups call for global reduction in black-carbon emissions to minimize human-induced global warming.