Seeing Through the Smoky Pall:
Observations from a Grim Indonesian Fire Season
In September and October 2015, tens of thousands of fires sent clouds of toxic gas and particulate matter into the air over Indonesia. Despite the moist climate of tropical Asia, fire is not unusual at this time of year. For the past few decades, people have used fire to clear land for farming and to burn away leftover crop debris. What was unusual in 2015 was how many fires burned and how many escaped their handlers and went uncontrolled for weeks and even months.
To study the fires, scientists in Indonesia and around the world have been using many different tools—from sensors on the ground to data collected by satellites. The goal is to better understand why the fires became so severe, how they are affecting human health and the atmosphere, and what can be done to prepare for similar surges in fire activity in the future.
In the darkest days of 2015, the smoke was so thick over Indonesia that satellite sensors like the Moderate Resolution Imaging Spectroradiometers (MODIS) on NASA’s Terra and Aqua satellites could barely see the lush tropical forests and expanses of cultivated land below. On many days, they saw acrid gray clouds of smoke hanging over Sumatra and Kalimantan (southern Borneo) instead.
On the ground, measurements from air pollution sensors were off the charts. In parts of southern Sumatra and Borneo, Indonesia’s Pollutant Standards Index (PSI)—which incorporates particulate matter, sulfur dioxide, nitrogen dioxide, carbon monoxide, and ozone—soared above 2,000. Any score above 350 is considered hazardous to human health.
NASA maintains a global network of ground sensors—AERONET—that helps validate satellite measurements of airborne particles, or aerosols. A station in Palangkaraya, one of the most severely affected cities in Borneo, detected a six-fold increase in particles compared to the usual levels for September and October. “We have never seen such a persistently high value from any of our AERONET sites for such a long period,” said Brent Holben, a scientist at NASA’s Goddard Space Flight Center.
Government authorities and people on the street did what they could to respond to the dangerous air quality. Schools were shuttered. Some people stayed indoors and wore masks when they ventured outside. The Indonesian navy sent ships to smoke-affected provinces to serve as backup evacuation centers. A spokesperson for Indonesia’s Meteorology, Climatology, and Geophysics Agency called the fires “a crime against humanity.” The mayor of Pekanbaru, a city in Sumatra, issued an order to evacuate infants younger than six months to a town hall that had been outfitted with air filters, cribs, and air conditioners.
By the time monsoon rains arrived in late October and many of the fires were quenched, government sources reported 19 pollution-related deaths. Some 500,000 people suffered respiratory problems, and more than 43 million were exposed to unusually high levels of smoke.