A Snapshot of Particles in the Air

Tiny solid and liquid particles—some you can see, some you cannot—can be found in the air everywhere on the planet, at any time of year. The amount of particles, known to scientists as aerosols, fluctuates naturally with the seasons and natural events, as well as with human activities. Dust storms, volcanic eruptions, wildfires, and salt spray from the winds over the ocean are the most common and abundant producers of aerosols. Humans generate them, too, through the burning of fossil fuels, manufacturing processes, and fires for cooking, heating, and agricultural clearing.

This map shows the global distribution of aerosols in August 2010, and the proportion of those aerosols that are large or small. Yellow areas are predominantly coarse particles, like dust and sea salt, while red areas are mainly fine aerosols from smoke or pollution. Gray indicates areas with no data. The brighter or more intense the color, the higher the concentration of aerosols.

The map was compiled from data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites.

Yellow bands—larger, coarse particles—around the Middle East, North Africa, and western North America likely indicate dust and sand storms as the northern hemisphere reaches the driest time of year. The bright red areas in Russia and much of South America reveal the intense wildfires and some agricultural burning, which coincided with hot summers and drought in several regions. The red patches in western Canada spring from summer wildfires, while China was likely coping with a combination of fire, dust, and pollution events. It is unclear what was happening in western Africa.

Of all the particles that fill our lungs on any given day, the most dangerous are the small ones. Aerosol particles smaller than 2.5 micrometers pose the greatest risk to human health because they are small enough to be breathed deep into the lungs and, in some cases, enter the blood stream. These fine particles, about 30 times smaller than the width of a human hair, are also a major cause of poor visibility.

NASA map by Robert Simmon, based on MODIS data from NASA Earth Observations. Caption by Mike Carlowicz.

Instrument:
Terra - MODIS
Nasa Earth Observatory del 25 dicembre 2010

Dust in the Wind

Tiny solid and liquid particles—scientists refer to them as aerosols—can be found in the air all over the world, and they have a global impact on weather and climate. There are many sources of aerosols, including smoke and pollution from human activities. One of the most abundant particles is the dust and sand that blows off of Earth's deserts.

This series of images, derived from a computer model, shows wind-blown dust from North Africa as it spread over the Atlantic Ocean on July 1, 2009. The model depicts aerosol optical thickness, a measure of the amount of light that the aerosols scatter and absorb, and a proxy for the number of particles in the air. An optical thickness of less than 0.1 indicates a clear sky with maximum visibility; a value of 1 or above indicates very hazy conditions. The time signatures in the model move in six-hour increments from midnight (00:00 Universal Time, or UTC) to 6 p.m. (18:00).

Although most aerosols remain suspended in the air for just short periods—typically between four days and a week—they can travel vast distances. Particles moving with the atmosphere at 5 meters (16.4 feet) per second will travel thousands of kilometers in a week.

Dust plumes from the Sahara frequently cross the Atlantic and reach the skies of the Caribbean. Scientists are particularly interested in the role of this dust transport in the formation of clouds and in influencing the development of hurricanes and typhoons.

As noted in our fact sheet, “Aerosols: Tiny Particles, Big Impact”:

Most elementary school students learn that clouds form when enough water vapor condenses. That’s true, but aerosols play a critical role in the process. In fact, most clouds owe their existence to aerosols that serve as the tiny “seeds,” called cloud condensation nuclei. Natural aerosols are the most common condensation nuclei in pristine environments.

The event depicted above comes from the Goddard Earth Observing System Model, Version 5 (GEOS-5), an atmospheric model used to study the physics of the atmosphere in both the short term (weather) and mid- to long term (climate). The GEOS-5 model uses mathematical equations that represent physical processes—such as precipitation and cloud processes—to calculate what the atmosphere will do. Actual measurements of physical properties like temperature, moisture, and winds are routinely folded in to keep the simulation as close to the real world as possible.

The millions of calculations involved in creating such a detailed global model require thousands of computer processors. The GEOS-5 model runs on the nearly 15,000 processors of the Discover supercomputer in the new NASA Center for Climate Simulation at Goddard Space Flight Center.

NASA maps by Pete Colarco and Robert Simmon, based on GEOS-5 model data. Caption by Mike Carlowicz and Adam Voiland.

Instrument:
Model

Earth Observatory, Imge of the day 18th December 2010

Ecoscienza - ARPA Emr

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Seasonal Changes in Indian Aerosols

In recent years, scientists have detected very high levels of aerosol pollution in the air over India. Some of it is the result of industrial and agricultural activity, and some of it is nature at work. New research released this fall shows that the amount, size, and source of the aerosol particles hovering in the air over India changes by season.

These maps were built from data from the Multi-angle Imaging Spectroradiometer (MISR) instrument on NASA’s Terra spacecraft. The top image shows aerosol optical depth, a measure of the amount of light that the aerosols scatter and absorb in the atmosphere, and a proxy for how many particles are in the air. The lower map shows the likely source—natural or human-made (anthropogenic)—based on the size of the particles and other factors. Data depicted are averages for the pre-monsoon season (March through May), the monsoon (June to September), post-monsoon (October, November), and winter (Dec to Feb) for the years 2000 to 2008.

Aerosols are tiny solid and liquid particles suspended in the air, and they come from many natural sources, including volcano emissions, sand and dust storms, and salt from sea spray. Nearly 90 percent of all aerosols (by mass) arise naturally, and most tend to be relatively large particles. The rest of the aerosol load in the air comes from man: sulfates, black and brown carbon, and other pollutants associated with the burning of fossil fuels and of agricultural land. Aerosols produced by human activity tend to be smaller and more damaging to human lungs.

Researchers Sagnik Dey and Larry Di Girolamo of the University of Illinois at Urbana-Champaign assembled and analyzed nine years worth of measurements and found that the level of aerosol pollution was, depending on the season and location, two to five times higher than World Health Organization guidelines. More significantly, the dominant sources of the pollution shift with seasonal weather patterns.

In the spring months leading up to the monsoon, winds blow onshore and inland, carrying dust from Africa and the Arabian peninsula…and something more. “Just before the rains come, the air gets really polluted, and for a long time everyone blamed the dust,” said Di Girolamo. “But MISR has shown that there’s also a massive buildup of manmade pollutants hidden within the dust.”

The rains of the monsoon tend to wash dust and soot from the air, though some anthropogenic pollutants build up. After monsoon season, damp ground means dust transport is reduced, while human-made pollutants skyrocket because of land-clearing for farming and because weather patterns do not disperse vehicle exhaust. During winter, seaward-blowing breezes disperse all the pollutants across the subcontinent and out to sea.

Articolo di Nasa Earth Observaotory del 24 novembre 2010

Global View of Fine Aerosol Particles

Articolo su Earth Observatory del 9 novembre 2010