Small Airborne Particles Are Powerful Enough to Change the Climate
Small Airborne Particles Are Powerful Enough to Change the Climate
Good things come in small packages, according to an old aphorism. The author of the quote definitely wasn’t a researcher in bioaerosols and other airborne pollutants. In the scientific realm, smaller often means deadlier.
Increasingly, researchers are confirming that small airborne particulates represent the greatest danger to health, longevity and quality of life for affected populations. Most surprisingly, these tiny pollutants are powerful enough to change established weather patterns across the globe.
“Aerosols are a mix of suspended liquid and solid particles in the air with distinctive chemical compositions,” writes Anuradha Varanasi on Columbia University’s Climate School State of the Planet site. “The smaller the size of an aerosol, the more severe its health impacts. Particulate matter with a diameter of less than 2.5 microns (PM2.5) can easily infiltrate the lungs. PM2.5 has been associated with higher rates of respiratory, autoimmune, and neurological disorders than a comparatively bigger PM with a diameter of 10 microns or less.”
Small particles have the ability to generate major climate changes, as well. “Although microscopically tiny, aerosol particles can have mighty impacts on the atmosphere and climate. Major volcanic eruptions and their resulting aerosol emissions high up in the atmosphere are infamous for altering monsoon circulations and precipitation patterns around the world, even triggering severe droughts in Eastern China and India.”
The most dangerous particulates originate from manmade sources. “The majority of anthropogenic aerosols are made in the atmosphere from gas molecules,” explains Varanasi. “For example, during the coal burning process, the sulfur present in coal becomes oxidized and gets released into the atmosphere as sulfur dioxide gas. The gas then reacts with clouds, water vapor, and other pre-existing compounds before it transforms into sulfate aerosols that have a cooling effect on the lower atmosphere.”
Ironically, for many decades sulfate aerosols were having a cooling effect on the planet. Now that many developed countries have reduced emissions of these particulates, the cleaner air has led to greater warming.
“Similar to sulfate particulate matter, other anthropogenic aerosols like nitrates and airborne microplastics also scatter and deflect solar radiation back to space, leading to atmospheric cooling,” she notes. “Certain forms of organic carbon could also have a net cooling influence by scattering sunlight away from the Earth’s surface.”
Warming has, in turn, increased the amount of ozone pollution in many regions, especially in China. “Warmer temperatures ramp up reactions between nitrogen oxides and volatile organic compounds that get trapped in the lower atmosphere. Researchers observed that getting rid of aerosols or fine particulate matter is another reason why Chinese cities are experiencing a spike in ozone pollution.
“Previously, high levels of PM2.5 in the air acted like sponges that efficiently absorbed the radicals responsible for generating ozone pollution. The aerosols consistently inhibited ozone production. By aggressively tackling the sources of sulfur dioxide emissions, China inadvertently tinkered with the atmosphere’s chemistry. Once the sulfate-dominated PM2.5 concentrations started depleting, more sunlight and radicals were left behind to produce ground-level ozone.”
Varanasi points out that a volcanic eruption by Mount Pinatubo in the Philippines in 1991 lowered global temperatures by up to a half degree Celsius for the next two years. Up to 20 million tons of noxious sulfur dioxide gas were released into the stratosphere, forming mists of tiny sulfate aerosols.