Aerosols’ Pollution of Our Atmosphere
When we think of aerosols, we think of hairsprays, paints, fabric softeners, cooking sprays, various cleaning products, spray-on deodorant, or air fresheners. We’ve been chided in the last number of years for using these products: they put more chemicals into our atmosphere! We’re only making our air more polluted! Stop, stop, stop! But what I’ve noticed is that, despite this pestering, there has been a lack of explanation. We have a very narrow idea of what aerosols are, and the true damage that their pollution has on the atmosphere. In this post, I aim to define what aerosols are, the ones that cause the most harm, and why exactly our environment is put at great risk.
According to a particle published by NASA in 1996, aerosols are defined as tiny particles that are suspended in the atmosphere that, as they grow larger and larger, scatter throughout Earth’s atmosphere and absorb a substantial amount of sunlight (1). The majority of aerosols found in our atmosphere, nearly 90% by mass (2), originate from natural sources. Examples of these sources are black carbon, biomass burning aerosols, mineral dust, sea salt, organic aerosols, sulfate/nitrate aerosols, volcanic aerosols, cloud condensation nuclei, forest fires, certain plants that produce gases that will react with substances in the air, and even in the ocean, where there are types of micro-algae that produce a sulfurous gas known as dimethyl-sulfide that can convert into sulfates in the atmosphere (3). But even though I’ve just listed off several examples of natural aerosol produces, NASA highlights three that significantly impact Earth’s climate, and I want to take a moment to focus on them.
The first is the volcanic aerosol layer. Following major volcanic eruptions, the aerosols will form in the stratosphere. The dominant layer will be made up of sulfur dioxide gas which converts to droplets of sulfuric acid over the course of several days following the eruption. These particles are also spread around by the wind in the stratosphere, allowing them to span over several parts of the globe. These aerosols, once they’ve comfortably formed, can remain in their places for approximately two years where they will reflect sunlight, reducing the amount of energy reaching the lower atmosphere and Earth’s surface — this ultimately plays a significant role in cooling these areas (1).
The next type of aerosol is desert dust, which is a dramatic term used to describe dust veils that several satellites have found throughout the world. These clouds are made up of tiny particles of dirt that have blown away from the desert surface. The dust particles themselves are made up of minerals that absorb sunlight while at the same time scattering it. By absorbing the sunlight, the dust particles warm the layer of the atmosphere where they dwell, which scientists have found makes it more difficult for storm clouds to form, ultimately relating directly to a lack of rain. This suppression is believed to cause a dust veil which only furthers desert expansion (1).
And the third culprit? Well, it’s time for us to look in the mirror for this one. Anthropogenic, or human-made, aerosols are responsible for the remaining 10% of aerosols found in our atmosphere (2). Though considerably less ample, these aerosols can dominate the air near urban and industrial communities (3). Scientists explain that the burning of fossil fuels, a practice that society desperately depends on despite its horrific impacts on our environment, produces large amounts of sulfur dioxide, which then reacts with gases in the atmosphere, specifically water vapor, to create sulfate aerosols. Sulfate aerosols reflect sunlight, which reduces the amount that then reaches Earth’s surface (1). They also can reportedly enter clouds, causing the number of cloud droplets to increase but the droplet sizes themselves to get smaller. By doing this, clouds are believed to reflect more sunlight than they would if the sulfate aerosols had not been introduced into the atmosphere (1). Biomass burning is another habit — one that humans use to clear large areas of land and consume farm waste. By doing so, it releases smoke that consists of black carbon which is considered an absorber of incoming sunlight.
What else though? So far it seems like I’ve only been throwing big words at you that have little to no meaning. How does any of this apply to your life? Think about when you get up in the morning. You use your car to drive to work, and on your way, you pass hundreds of other vehicles on the road. By doing this, each of these automobiles are producing sulfates, nitrates, black carbon, and other particles into the air. The roads you drove on were once nonexistent as there were miles of trees instead. This land was taken away to be replaced by these human-paved roads. This is an example of deforestation, or an altering of the land surface, which increases the rate at which dust particles enter the atmosphere. Think about all of the pollutants being released when someone lights a cigarette, or when a wood-burning fireplace is releasing smoke from its chimney, or even lighting a candle — these are all sources of aerosols in our daily lives.
So what’s happening then? Let’s look at the sun. The sun provides the Earth with energy which then drives its climate. But not all of this energy that reaches the very top of our atmosphere actually makes it all the way to the surface of Earth because the aerosols and the clouds that are made up of them reflect nearly a quarter of this energy back up into space. There are also some aerosols that absorb this sunlight as I mentioned before, one being black carbon. Unlike pure sulfates and nitrates, both of which reflect the majority of radiation that they encounter, black carbon is an example of an aerosol that will absorb the sun’s radiation, warming the atmosphere but also shading Earth’s surface. There are several other natural aerosols that respond to light differently, but the general idea is that an individual particle’s effect on light depends on its composition and the color of its particles (3).
I want to draw all of this in and focus on the impact that aerosol pollution has on our environment. Interacting with the climate in a direct way, aerosols reflect sunlight and cool the planet. In an indirect way, aerosols influence the properties of our clouds. By increasing the number of aerosols in our atmosphere, it alters the amount of clouds and the thickness and frequency of rainfall (4). From all of this information, it seems like we can draw a few conclusions: first, aerosols originate from so many more sources than most people realize. Second, there seems to be two main impacts that our climate is experiencing — the cooling of Earth’s surface, and the influence on cloud structure and rain frequency. And though you might notice that unlike greenhouse gases that are warming Earth’s surface, the majority of aerosols are cooling the earth. Then why are aerosols so bad when they’re working against the foul greenhouse gases? What scientists are saying is this: they don’t have a lot of clear, definitive data that shows the impact of aerosols on the environment. There are even some computer models that suggests that anthropogenic aerosols’ cooling of Earth’s surface could potentially counterbalance the greenhouse gas warming by an approximated 30% (4). But there is no evidence that really proves this one way or another. Until there’s more research done that outlines the long-term effect that aerosols have on our atmosphere, we should continue to look at them as pollutants escaping into our atmosphere that should be limited as best as we can.
Bibliography
Allen, B. Atmospheric Aerosols: What Are They, and Why Are They So Important? https://www.nasa.gov/centers/langley/news/factsheets/Aerosols.html (accessed Nov 4, 2018). 1
Voiland , A. Aerosols: Tiny Particles, Big Impact https://earthobservatory.nasa.gov/Features/Aerosols/page1.php (accessed Nov 4, 2018). 2
Laboratory, O. R. N. Aerosol Particle Types and Characteristics http://cdiac.ess-dive.lbl.gov/aerosol_particle_types.html (accessed Nov 4, 2018). 3
Aerosols https://enviroliteracy.org/air-climate-weather/climate/aerosols/ (accessed Nov 5, 2018). 4
