Smoke is an international traveler that moves with the wind and weather across borders. On March 24, 2004, smoke from fires in Southeast Asia—as far away as India—has stretched thousands of kilometers away, and hangs in a dirty-looking haze across a bank of clouds over the South China Sea. At this time of year, agricultural burning takes place across Southeast Asia as both large- and small-scale farmers clear land for planting or grazing. To the north, the haze may include some dust, as dust storms have been sweeping across the Taklimakan and Gobi Deserts in northern China in mid-March.
Smoke from burning vegetation contains a lot of particulate matter. When such pollution particles are smaller than 10 microns (1 micron is one-millionth of a meter, only a fraction of the diameter of a human hair) it is especially dangerous to human health. Particles that tiny evade our lungs’ defenses and our immune systems much more easily than larger particles. Dust is known to be a carrier of disease. Both dust and smoke reduce visibility and decrease sunlight reaching the Earth’s surface, which in turn affects productivity in crops and other plants. The study of these and other aerosols in our atmosphere is a key component of NASA’s ongoing Earth science and climate change research efforts.