Archives for category: Air Quality
indonesia_fires

(Photo by Martin Wooster.)

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.

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NASA Earth Observatory, March 2015

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When astronauts talk about viewing Earth from space, the conversation often turns to the planet’s mesmerizing beauty. They describe views of aquamarine coral reefs glimmering amidst the deep blue ocean; of armies of sand dunes marching across deserts; of clouds and lightning flashes dancing through the atmosphere.

For many, the view is deeply humbling. “For the first time in my life, I saw the horizon as a curved line. It was accentuated by a thin seam of dark blue light: the atmosphere,” said Ulf Merbold, a German astronaut who flew on Space Shuttle Columbia in 1983. “This was not the ‘ocean’ of air I had been told it was…I was terrified by its fragile appearance.”

For some astronauts, that thin blue line has appeared quite vulnerable. Many have noticed palls of haze lingering over parts of the world, the result of millions of tiny particles drifting in the atmosphere. Aerosol particles, which can be either liquid or solid, obstruct sunlight and cause distinct and vibrant features to blend into a hazy, featureless mélange of gray.

The particles that affect visibility have many sources, some of them natural. For instance, winds blow bits of dust and dried soil aloft; volcanoes occasionally belch thick plumes of ash; forest fires produce smoke; even vegetation and plankton can emit substances that contribute to haze.

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NASA Earth Observatory, June 2014


For more than a decade, scientists have observed “ship tracks” in natural-color satellite imagery of the ocean. These bright, linear trails amidst the cloud layers are created by particles and gases from ships. They are a visible manifestation of pollution from ship exhaust, and scientists can now see that ships have a more subtle, almost invisible, signature as well.

Data from the Dutch and Finnish-built Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite show long tracks of elevated nitrogen dioxide (NO2) levels along certain shipping routes. NO2, is among a group of highly-reactive oxides of nitrogen, known as NOx, that can lead to the production of fine particles and ozone that damage the human cardiovascular and respiratory systems. Combustion engines, such as those that propel ships and motor vehicles, are a major source of NO2 pollution.

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Earth Observatory, February 2013

As is often the case in the winter, a thick river of haze hovered over the Indo-Gangetic Plain in January 2013, casting a gray pall over northern India and Bangladesh. On January 10, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this image of haze hugging the Himalayas and spilling out into the Ganges delta and Bengal Sea.

The haze likely resulted from a combination of urban and industrial pollution, agricultural fires, and a regional meteorological phenomenon known as a temperature inversion. Usually the air higher in the atmosphere is cooler than the air near the surface, a situation that allows warm air to rise and disperse pollutants. However, cold air often settles over northern India in the winter, trapping warmer air—and pollution—close to the surface, where it has the greatest impact on human health.

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Earth Observatory, February 2013

Many types of aerosol particles circulate in the atmosphere, but one of the most damaging to human health is known as PM2.5, a technical term for microscopic bits of matter less than 2.5 microns in diameter (one thirtieth the width of a human hair). These small pollutants, which come mostly from burning fossil fuels and biomass, can lodge deep in the lungs, where they exacerbate a variety of respiratory and cardiovascular diseases.

Ground-based instruments are the standard for monitoring PM2.5 in many industrialized nations. For example, the U.S. Environmental Protection Agency, along with state and local governments, maintain a network of about10,000 ground stations that generate real-time air quality measurements for hundreds of cities. Such data gets funneled into services like AIRNow, which issues warnings when pollution reaches unsafe levels.

However, not all countries have ground-based monitoring systems that measure such fine-grained pollutants.China, like most countries, has traditionally only monitored a larger type of particle pollution known as PM10. Though Chinese leaders have announced a plan to monitor PM2.5 more broadly in the future, to date only a handful of cities have started to publish PM2.5 numbers.

Satellites offer a perspective on PM2.5 that is particularly useful when ground instruments are unavailable or offer limited information. With that in mind, researchers at Columbia University’s Earth Institute and Batelle Memorial Institute have developed maps based on satellite data that depict annual PM2.5 exposure in all of China’s provinces.

The map above, which shows annual exposure between 2008-2010, indicates that most areas had PM2.5 levels that exceeded World Health Organization guidelines (10 micrograms per cubic meter). Areas surrounding Beijing and to the south along the coast, which fall in China’s industrial heartland, had the most pollution. In many cases, annual exposure was above 40 micrograms per cubic meter. Other provinces in eastern and south central China had pollution levels above 30 micrograms per cubic meter. For comparison, the New York, Chicago, and Los Angeles metro areas have PM2.5 levels that average between 10 and 20 micrograms per cubic meter.

The values used to create the map were derived from a method that Dalhousie University scientist Aaron van Donkelaar developed and published in Environmental Health Perspectives in 2010. At the time, van Donkelaar released a global map of PM2.5 pollution. Both that map and the map above are based on data from the Multi-angle Imaging Spectroradiometer (MISR) instrument on the Terra satellite, the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on the Terra and Aqua satellites, and a chemical transport model calledGEOS-Chem.

While satellite measurements are the best option in areas with limited ground monitoring, they are not without shortcomings. Satellites, for example, have difficulty detecting pollution over bright surfaces, such as snow and deserts. Overall, the researchers say the uncertainty amounts to about 6.7 micrograms per cubic meter.

NASA Earth Observatory, March 2012

A new study led by a NASA scientist highlights 14 key air pollution control measures that, if implemented, could slow the pace of global warming, improve health and boost agricultural production.

The research, led by Drew Shindell of NASA’s Goddard Institute for Space Studies (GISS) in New York City, finds that focusing on these measures could slow mean global warming 0.9 ºF (0.5ºC) by 2050, increase global crop yields by up to 135 million metric tons per season and prevent hundreds of thousands of premature deaths each year. While all regions of the world would benefit, countries in Asia and the Middle East would see the biggest health and agricultural gains from emissions reductions.

“We’ve shown that implementing specific practical emissions reductions chosen to maximize climate benefits would also have important ‘win-win’ benefits for human health and agriculture,” said Shindell. The study was published today in the journal Science.

NASA, January 2012