Aerosol particles at global view

Nov 10, 2010

Of all the pollution that fills our lungs on any given day, the most dangerous is the small stuff. Aerosol particle pollution—airborne solid particles and liquid droplets--comes in a range of sizes. 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.

This map provides an estimate of the average distribution of fine near ground-level throughout the world. The highest concentrations of fine particles, called PM (particulate matter) 2.5, hover over highly industrialized areas in eastern Asia. The high concentrations over northern Africa and the Middle East are likely fine dust from the deserts. The World Health Organization’s Air Quality Guidelines recommend that concentrations of particulate pollution should not exceed 10 micrograms per cubic meter. When compared with global population, the map reveals that 80 percent of the world’s people live in areas that exceed that value.

The map was compiled from satellite measurements (acquired between 2001 and 2006) and from model data. Both the Multi-angle Imaging SpectroRadiometer (MISR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite measure particle pollution (). The GEOS-Chem model was used to help researchers determine how much of the satellite-measured pollution was at ground level, where it poses a threat to human health.

comes from a variety of sources, as detailed in the Earth Observatory’s new fact sheet, Aerosols: Tiny Particle, Big Impact. The following is an excerpt.

The bulk of aerosols—about 90 percent by mass—have natural origins. Volcanoes, for example, eject huge columns of ash into the air, as well as sulfur dioxide and other gases, yielding sulfates. Forest fires send partially burned organic carbon aloft. Certain plants produce gases that react with other substances in the air to yield aerosols, such as the “smoke” in the Great Smoky Mountains of the United States.

Sea salt and dust are two of the most abundant aerosols, as sandstorms whip small pieces of mineral dust from deserts into the atmosphere and wind-driven spray from ocean waves flings sea salt aloft. Both tend to be larger particles than their human-made counterparts.

The remaining 10 percent of aerosols are considered anthropogenic, or human-made, and they come from a variety of sources. Though less abundant than natural forms, anthropogenic aerosols can dominate the air downwind of urban and industrial areas.

Automobiles, incinerators, smelters, and power plants are prolific producers of sulfates, nitrates, black carbon, and other particles. Deforestation, overgrazing, drought, and excessive irrigation can alter the land surface, increasing the rate at which dust aerosols enter the atmosphere. Even indoors, cigarettes, cooking stoves, fireplaces, and candles are sources of aerosols.

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More information: Donkelaar, A., et al. (2010, June). Global estimates of ambient fine particulate matter concentrations from satellite-based aerosol optical depth: development and application. Environmental Health Perspectives, 118 (6). Accessed November 4, 2010.

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not rated yet Nov 10, 2010
Too bad they can't get data over the other 80% of the earth's surface. The satellites don't see well over water, high elevation or rough terrain. Not to mention that it's daylight only. I wonder if day vs night makes a difference with aerosols though? Anyway, it would be neat also if we had a long enough data set to see trends. Still, this snapshot is better than nothing. I wonder which poses a larger threat to humans and wildlife; aerosols or GHG's?
not rated yet Nov 13, 2010
I wonder which poses a larger threat to humans and wildlife; aerosols or GHG's?

I imagine it's a matter of location and degree. Some areas in China have horrifically polluted air. For a good example of the health effects of air pollution, just look at London Fog. Any population living in such highly air faces immediate and severe consequences.

Humanity as a whole, however, is almost certainly more challenged by potentially game-changing GHGs and other problems. We can afford to lose slightly more of the vulnerable (old, young, poor) every year, but we can't afford to relocate major population centers or severely impact industry.
not rated yet Nov 14, 2010
I'm not a good person to judge such a question myself. I'm not surprised that you are so quick to make a judgement. Most people these days feel that they MUST have a belief. It's uncommon for people to accept that some questions aren't answered yet. We all want to think we know everything, so it seems.

I will challenge your statement only in so far as to say that your opinions are not fully supported by the facts. There are too many factors that you have not taken into account, and far too many unanswered questions to say what our greatest threat is right now. If you are talking about sea level rise, when you talk about relocating cities, then I think you are a little crazy, no offense.
not rated yet Nov 14, 2010
... and I'm not surprised that you're so quick to judge me ;). It's similarly unsurprising that many people want to see 100% confidence before recommending policy changes, rather than accepting 90% or 95%.

There are plenty of issues I refrain from judging on, but on this issue there is enough evidence to make an informed, tentative conclusion. Particulate matter has a powerful local effect, and has a well-documented impact on health. Assuming the IPCC's conclusions have even a slim 10% chance of being true, I think it's pretty darned safe to say that climate change poses a larger global threat.

As I said, we can absorb the current human losses and health effects/healthcare costs brought about by particulate matter. I'm not saying we shouldn't do anything about the problem, just that it's a manageable and localized one. The less-localized causes are largely out of our control.
not rated yet Nov 15, 2010
"just that it's a manageable and localized one"

That is not true. Aerosols from the central US drift a thousand miles to cause acid rain in Quebec. Aerosols from the Saharah desert drift all the way across the Atlantic and affect cloud formation in the Amazon. Ash from Mt St Hellen fell like snow in Ohio. I have two vials of it in my keepsake chest. I would not be so quick to say that aerosols are the least harmful of the two when compared to ghg's. The space agencies have only just begun to study aerosols, after all. They are not well understood and it still remains to be discovered what the magnitude of their effect is on global climate change. I'm not saying you are wrong, or that ghg's aren't harmful. I'm not saying that ghg's shouldn't be contained. I am just suggesting that aerosols could be even worse, because we really don't know how bad they are yet.

Ghg's could even have a positive net effect according to some. Warmer climate in tundra leads to biodiversity increase.

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