Archives for category: Aerosols

(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

Today is a big day. I just arrived in Los Angeles from DC this afternoon, and I’m heading to Vandenberg Air Force Base in Lompoc, California, to see an Atlas 5 rocket blast Landsat 8 into space. Officially, the satellite is called the Landsat Data Continuity Mission (LDCM) until it reaches orbit safely, but I’m going to call it Landsat 8 anyway in the spirit of keeping jargon to a minimum.

This is the second time I’ve been fortunate to have a front-row seat to the launch of one of NASA’s Earth-observing satellites. The mission that brought me to Vandenberg the first time was called Glory; it was a climate-centered mission, designed to measure aerosols and fluctuations in the amount of sunlight that reaches the top of Earth’s atmosphere.

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Earth Observatory, Earth Matters blog, 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 team of scientists have used the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite to confirm major reductions in the levels of a key air pollutant generated by coal power plants in the eastern United States. The pollutant, sulfur dioxide, contributes to the formation of acid rain and can cause serious health problems.

The scientists, led by an Environment Canada researcher, have shown that sulfur dioxide levels in the vicinity of major coal power plants have fallen by nearly half since 2005. The new findings, the first satellite observations of this type, confirm ground-based measurements of declining sulfur dioxide levels and demonstrate that scientists can potentially measure levels of harmful emissions throughout the world, even in places where ground monitoring is not extensive or does not exist. About two-thirds of sulfur dioxide pollution in American air comes from coal power plants. Geophysical Research Letters published details of the new research this month.

The scientists attribute the decline in sulfur dioxide to the Clean Air Interstate Rule, a rule passed by the U.S. Environmental Protection Agency in 2005 that called for deep cuts in sulfur dioxide emissions. In response to that rule, many power plants in the United States have installed desulfurization devices and taken other steps that limit the release of sulfur dioxide. The rule put a cap on emissions, but left it up to power companies to determine how to reduce emissions and allowed companies to trade pollution credits.

NASA, December 2011

On a warm afternoon in early March, the Taurus XL rocket that was prepped for launch at Vandenberg Air Force Base in Southern California looked more like a giant chopstick standing on end than a potential game changer in the debate over climate change science.  The barrel-shaped satellite that the rocket carried — named Glory — was designed to deliver critical information about small airborne particles called aerosols. The elusive particles account for much of the uncertainty in climate models, and data from the satellite would have helped scientists determine more of the aerosols’ key properties than ever before....

Earth, September 2011