Hunt for Aerosol Agents

NASA Goddard Institute for Space Studies

Layer of aerosols injected into the atmosphere from the eruption of Mount Pinatubo

What is the profile of aerosol agents?

Answering this question is key to understanding aerosol agents and foiling a potentially global plot underway that could potentially warm the planet to the point of no return. This is not an easy mission. The GISS team must identify all the different kinds of aerosols, where they are found (sources), what they look like (size, shape and composition), how many exist, how they move around our planet, how they interact with other particles and gases and what are their effects on sunlight (reflect it or absorb it).

Aerosols are a formidable nemesis for the GISS team and the entire science community. The real challenge is that aerosols function as a global organization made up of millions of individual airborne particles with many powers that make tracking them difficult, such as the ability to:

  • Disguise themselves in a wide variety of chemical compounds and physical properties like sizes, shapes and color
  • Carry out operations over a short time period and then disappear
  • Be transported around the world in water and air, contributing to their variability from place to place
  • Interact with other gases and clouds and change properties and impacts
  • According to GISS Scientist, Dorothy Koch, an important reason global aerosols are poorly measured and continue to elude us is because they can "multi-task to change the climate.”

Global Aerosol Sources
Global Aerosol SourcesCourtesy NASA Earth Observatory

The GISS team's investigation takes them around the world to find where aerosols come from (the source) and whether they are natural or human-created.

Natural sources, like volcanic eruptions, can produce a global aerosol event by spewing huge amounts of ash and sulfuric acid into the atmosphere. Former GISS scientist, Richard Stothers, knew Volcanoes, Past and Present provide fantastic experiments happening in the real world to study the global cooling effect of aerosols. In 1991, the eruption of Mount Pinatubo provided scientists with one of the most violent events in recent history.

Other natural sources are fires in forests and on grassy plains that emit black or even brown carbon aerosols, depending on how hot the fire is. Winds over the world's oceans generate the sprays of droplets that form sea salt aerosols and over the desert gusts of wind lift small particles of dust from the surface to form clouds of dust aerosols that can travel thousands of miles, even crossing the Pacific and Atlantic oceans. A more subtle natural source of particles are gases emitted by plants in the ocean and on land that can condense out onto particles, or even form new particles.

A smaller, potentially more dangerous group of aerosol agents operate under cover in everyday human activities. These so-called anthropogenic aerosol sources can mainly be traced to the burning of fossil fuels like coal, oil and gas. Other aerosols enter our air as a by-product of these human activities as sulfur dioxide, but then interact with other atmospheric agents, like water vapor, and turn into sulfate particles.The GISS team also hunts human-made aerosols in land areas we clear of vegetation for agriculture by burning which creates brown and black carbon just like buying natural fires.

Aerosols from natural and human sources also work together. In South Asia's Tibetan Plateau desert dust mixes with black carbon from industrial pollution, biomass burning and forest fires. It is a dangerous interplay that maybe changing weather and rainfall patterns on the Asian Monsoon season.

Source: NASA Earth Observatory, Average monthly aerosol amounts

Since the most aerosols (heaviest concentrations) are found close to their source, this is the best way to find their their hideouts. For example, India, China and the U.S. are among the worlds’ biggest consumers of fossil fuels, so we know these areas are big hideouts for these aerosols sources. Likewise, Brazil, Indonesia and Africa are areas where deforestation is happening at an increasing rate, so this is a big hideout for aerosols emitted from biomass burning.

Aerosols disguise themselves in various sizes and shapes. This influences how they move around the planet and how much sunlight they scatter or absorb.

To find whether an aerosol is on a cooling or warming mission, the GISS team must get a measure of the single scattering albedo (a quantity ranging from 0 to 1). The closer to 1 an aerosol particle is, the better a cooling agent. The aerosol agents that measure closer to 0 are the ones with the greatest ability to absorb sunlight and are the ones we have to worry about in our already warming world.

Aerosols are also made up of different properties or composition. Whether they are composed of sulfates, nitrates, black carbon, soot or some combination is another factor that tells us about an aerosol's radiative capabilities to absorb or reflect sunlight, warm or cool and interact with other climate agents.

Composition tells us about how long different aerosols have to carry out their climate mission and whether their mission will effect people locally and/or globally. If volcanic aerosols are involved, they can travel into the upper atmosphere and last for 1-2 years. If aerosols from dust storms or pollution agents are activated, they can only reach the lower troposphere and can easily removed within a few days after settling to the ground or being washed away by rain.

Asian Brown Cloud
Asian Brown CloudCourtesy NASA Goddard Space Flight Center
Aerosols can be transported from one region to another. Light dust particles are easily lifted up and carried by winds and clouds to perform regional and global missions, sometimes at great distances from the original source.

The "Asian Brown Cloud" describes a large polluted cloud of aerosols and other particulates created from various aerosol sources int he region. On a global scale, instruments aboard NASA satellites track African dust plumes traveling from the Saharan Desert across the Atlantic and settling down over the Caribbean. Similarly, aerosols from arid regions in Africa and Asia are transported to the America's, contributing to haze, pollution and weather. Aerosols even rain down on the Arctic. According to GISS scientist, Drew Shindell, this is likely due to the region's close proximity to Europe and North America, two of the world's biggest industrialized areas and among the largest emitters of aerosols over the past century. Essentially, sand and dust particles are moving around the planet, bringing different parts of the world into our backyards and interconnecting all our lives.

Hunting down aerosols, measuring them and understanding their global climate missions is critical to making informed informed choices for the future.

Polar Bears on Melting Ice
Polar Bears on Melting IceCourtesy USGS
Aerosols have the ability to both absorbed and scatter sunlight as they interact with other climate agents. Some aerosols agents are able to carry out the most subversive missions, overtaking unsuspecting cloud particles, changing cloud properties, and increasing their potential to produce life-threatening water cycle extremes, such as droughts and floods. Analysis by the GISS research team studying aerosols shows that the biggest climate effect is from aerosol-cloud interactions. Some of the greatest impacts are seen in the melting of Arctic snow and ice cover and retreating glaciers.