The role of atmospheric aerosols on the Earth system is a subject of growing interest due to their impact on the Earth-atmosphere climate system, air quality, and human health. Ground-based remote sensing has emerged as a powerful technique for characterizing the suspended aerosol. The term aerosol is a catch-all for many kinds of little bits of stuff that end up suspended in the atmosphere, from the surface of the planet to the edges of space. They can be solid or liquid, infinitesimally small or big enough to see with the naked eye.

Definitions

An aerosol (abbreviation of “aero-solution”) is a suspension of fine solid particles or liquid droplets in air or another gas. According to the Merriam Webster;

a suspension of fine solid or liquid particles in gas

but when we study environmental physics then we describe it in other terms or relate it with the atmosphere. It can be defined as Atmospheric Aerosols;

Atmospheric aerosol an aerosol contains solid or liquid particles in suspension (e.g., dust particles). In the atmospheric aerosol

  • Typical concentrations are 103 particles cm-3 (over the ocean), 104 particles cm-3 (over the country), and 105 particles cm-3 (over cities).
  • The size ranges from aggregates of a few hundred molecules (diameter about 1 nm) to the largest particles (about 10 μm). The removal of the aerosol from the atmosphere depends on the size of the particles.

Aerosols come from both natural and human sources—and sometimes both at once. Dust, for example, is scoured from deserts, the dried-out edges of rivers, dry lakebeds, and more. Its concentrations in the atmosphere rise and fall with climate; in cold, dry, periods in the planet’s history like the last ice age, more dust filled the atmosphere than during warmer stretches of Earth’s history. But humans have affected that natural cycle, making some places dustier than they otherwise would be and keeping other areas damp.

Types and Sources of Aerosols

There are sources, that we can use for the classification or the base for the types of aerosols. This is as follows,

  • Types according to sources

So, we will take an overview of these one by one briefly.

Types According to Sources

We can divide the aerosols into two categories based on the sources of the aerosols, these are as follows,

  • Natural aerosols
  • Anthropogenic(human-made) aerosols

Natural

The aerosols have the natural sources of origin known as the natural aerosols

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. Likewise, in the ocean, some types of microalgae produce a sulfurous gas called dimethyl-sulfide that can be converted into sulfates in the atmosphere.

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.

it also can be further divided into the two groups

  • Organic Aerosols
    • natural organic materials: smoke, pollen, spores, or bacteria
  • Inorganic Aerosols
    • natural inorganic materials: fine dust, sea salt, or water droplets

Anthropogenic

The aerosols have the sources of origin by the human known as the anthropogenic aerosols

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. Fossil fuel combustion produces large amounts of sulfur dioxide, which reacts with water vapor and other gases in the atmosphere to create sulfate aerosols. Biomass burning, a common method of clearing land and consuming farm waste, yields smoke that’s comprised mainly of organic carbon and black carbon.

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. The anthropogenic can be further divided into the following groups

  • Primary aerosols
    • Primary aerosols contain particles introduced directly into the gas.
  • Secondary aerosols
    • secondary aerosols form through gas-to-particle conversion or reaction of the primary aerosols.

Effects of Aerosols

Aerosols have an important influence on atmospheric chemistry and physics:

  • they affect the atmospheric chemical composition
  • they can reduce visibility
  • they have important impacts on air quality and human health (e.g., aerosols can cause breathing problems)
  • they serve as nuclei for cloud droplets or ice crystals in ice clouds

aerosols have a lot of other effects but we will discuss here the environmental effects as well the health effects, spatially the human health effects.

Health Effects

Acid rain causes diseases

Volcanic eruptions release large amounts of sulfuric acid, hydrogen sulfide, and hydrochloric acid into the atmosphere. These gases represent aerosols and eventually return to earth as acid rain, having several adverse effects on the environment and human life.

Surface Deposition of Pollutants

When aerosols absorb pollutants, it facilitates the deposition of pollutants to the surface of the earth as well as to bodies of water. This has the potential to be damaging to both the environment and human health.

Cause pandemic

Aerosols in the 20  μm range show a particularly long persistence time in air-conditioned rooms due to their “jet rider” behavior (move with air jets, gravitational fall out in slowly moving air); as this aerosol size is most effectively adsorbed in the human nose, the primordial infection site in Covid-19, such aerosols may contribute to the pandemic.

 

Lungs Diseases

Aerosol particles with an effective diameter smaller than 10 μm can enter the bronchi, while the ones with an effective diameter smaller than 2.5 μm can enter as far as the gas exchange region in the lungs, which can be hazardous to human health. Other indoor sources of air pollution such as gas cooking are associated with only minor reductions in lung function of children.

Cancer and Premature Births

New hazards were identified from nanoparticles indoors and outdoors. At workplaces in Austria, the most frequent source of hazardous particles in the submicron range (around 100 nm) is environmental tobacco smoke. Active and passive smoking is associated with 61% of male cancer mortality in  Austria and overall,  with about eleven thousand premature deaths annually (about 10,000 from active smoking and 1,000 from secondhand smoke), mainly from cardiovascular causes. Possibly effects of passive smoking have been underestimated because of the non-linearity of the dose-response curve and the higher prevalence of second-hand smoking in Austria compared to other countries.

Aerosols and Climate

Aerosols influence climate in two primary ways: by changing the amount of heat that gets in or out of the atmosphere, or by affecting the way clouds form.

Temperature Increase

little flecks of black carbon from burned coal or wood, absorbing heat from the sun as it beats down. That ends up warming the atmosphere, though it cools the surface of the Earth by preventing the heat from escaping. Overall, that effect is probably smaller than the cooling most aerosols induce—but it’s far from nonexistent, and the more carbon-based material that collects in the atmosphere, the more warming the atmosphere experiences.

Clouds Formation

Aerosols also influence how clouds form and grow. Water droplets coalesce readily around particles, so a particle-rich atmosphere promotes cloud formation. White clouds reflect the incoming sun, preventing it from getting to the surface and warming land or water, but they also absorb the heat that the planet is constantly emitting back outward, trapping it in the lower atmosphere. Depending on the cloud type and location, they can either warm their surroundings or cool them.

Suggestions

we can reduce the impacts of aerosols or stop them by the following practices,

  • Mainly by less use of aerosols
  • People awareness
  • 3R
  • Modernization of the agriculture
  • Increasing the literacy
  • More plantation
  • Sustainability programs
  • Self-analysis of the environment
  • Water conservation
  • Reduction of carbon emissions
  • Using public transport etc.

Conclusion

An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be natural or anthropogenic. Aerosols have a complicated suite of different effects on the planet, but humans have directly impacted their presence, abundance, and distribution. While the climate effects are complex, the health impacts are clear: More fine material in the air hurts human health. Despite great progress, many questions remain about the competing impacts of aerosols. Measuring particles within clouds remains challenging. Different types of particles can clump together to form hybrids that are difficult to distinguish. Changes in humidity or temperature can cause drastic changes in how certain aerosols behave and interact with cloud droplets. Most importantly, the quantitative uncertainties in the number of aerosols, and especially aerosol properties, need to be reduced. Only better measurements, and the more sophisticated computer modeling such measurements make possible, will provide the critical information that scientists need to fully integrate aerosol impacts into climate models and to reduce uncertainty about how the climate will change. so, we should take care of the above things.

Musawar Hussain

Musawar Hussain

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