Archives for category: Air Quality


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