Smog (Smoke + Fog), Aerosols and their Impact on Monsoon

The intricate interplay between atmospheric constituents such as SMOG and aerosols exerts profound effects on the dynamics of monsoon rain, a crucial climatic phenomenon sustaining agriculture and ecosystems in many regions across the globe. SMOG, a complex mixture of pollutants primarily comprising particulate matter, ozone, and nitrogen oxides, alongside aerosols—tiny suspended particles of solid or liquid—significantly influence the intricate balance of moisture, temperature, and atmospheric circulation essential for monsoon development. Their intricate interactions, both locally and globally, not only modulate precipitation patterns but also pose challenges to air quality and human health. Understanding the intricate relationships between SMOG, aerosols, and monsoon rain is imperative for effective climate mitigation and adaptation strategies in the face of escalating environmental challenges.

Table of Contents

SMOG

Smog is a term derived from “smoke” and “fog,” indicating a hazy atmospheric condition resulting from the combustion of substantial quantities of coal, vehicle emissions, and industrial fumes (primary pollutants).
It comprises soot particulates such as smoke, sulfur dioxide, nitrogen dioxide, and various other components.
There are at least two discernible types of smog: sulfurous smog and photochemical smog.

SULFUROUS SMOG

Sulfurous smog, commonly known as “London smog” due to its initial occurrence in London, is characterized by elevated levels of sulfur oxides in the atmosphere.
It arises from the combustion of sulfur-containing fossil fuels, with coal being a predominant source (given that coal served as the primary power source in London during the nineteenth century, and the consequences of coal burning became apparent in the early twentieth century).
The presence of moisture and a substantial concentration of suspended particulate matter in the air further intensify the effects of this type of smog.

PHOTOCHEMICAL SMOG

Photochemical smog, also recognized as “Los Angeles smog,” is prominently observed in urban areas with a high concentration of automobiles, with nitrogen oxides being the primary emissions.
This type of smog, known as summer smog, forms when pollutants like nitrogen oxides (considered primary pollutants) and organic compounds (also primary pollutants) undergo reactions in the presence of sunlight.
This reaction leads to the formation of ozone (a secondary pollutant).

The chemical process can be represented as follows:

Nitrogen Dioxide + Sunlight + Hydrocarbons = Ozone

(Ozone is beneficial in the stratosphere but, near the Earth’s surface, it contributes to global warming as a greenhouse gas.)

The resultant smog manifests as a light brownish coloration of the atmosphere, causing reduced visibility, damage to plants, eye irritation, and respiratory distress.

EFFECT ON WEATHER

The atmospheric pollution levels in cities like Los Angeles, Beijing, Delhi, Mexico City, and others experience an increase due to inversions that trap pollution close to the ground.
Inversions, particularly temperature inversions, play a significant role in this phenomenon.
Temperature inversion occurs when the normal atmospheric temperature pattern is reversed, with warmer air aloft trapping cooler air near the surface.
This inversion layer can trap pollutants, leading to heightened pollution levels. The effects of temperature inversions on weather are noteworthy.
The resulting smog, a combination of airborne particulate matter such as soot and invisible toxic gases like ozone (O3), carbon monoxide (CO), and sulfur dioxide (SO2), poses severe health risks to humans.
These pollutants are carcinogens, capable of causing cancer and contributing to various health issues, including sickness, shortened life expectancy, or even death.
Furthermore, temperature inversions accentuate the atmospheric conditions, reducing precipitation and exacerbating the effects of smog-related haze.
This haze, laden with pollutants, significantly lowers visibility and further contributes to the adverse environmental and health impacts associated with increased pollution levels.

AEROSOLS

Aerosols, tiny particles present in the atmosphere, can originate from both natural and human activities.
Naturally occurring aerosols include dust stirred by the wind, sea salt, and sulfate compounds produced through natural processes.
Plants also release organic materials into the air, contributing to natural aerosol formation.
On the other hand, anthropogenic activities generate aerosols such as soot, sulfates from fossil fuel combustion, fly ash from thermal plants, and nitrates from vehicular emissions, constituting a significant portion of atmospheric haze.
While naturally formed aerosols can play a role in cloud formation by providing a substrate around which water vapor condenses into droplets, aerosols released through human activities may have adverse effects on climate.
Aerosols, in contrast to greenhouse gases that persist in the atmosphere for extended periods, are short-lived. These fine particles remain aloft in the atmosphere for only one to three weeks.
The distribution of aerosols is not uniform globally; they tend to concentrate near their sources and can be transported across continents by winds.
The quantity and composition of aerosols in the atmosphere also vary seasonally, influenced by changing environmental conditions.

AEROSOL AND THEIR IMPACT ON MONSOON

Scientists have highlighted the significant impact of aerosols on India’s monsoon rainfall over the past 50 years.
The data suggests a decrease in monsoon rainfall due to aerosols, raising concerns about an increased frequency of droughts in the future if pollution continues unchecked.
Aerosols, by dimming sunlight over the Arabian Sea, cool that region compared to the southern Indian Ocean.
This cooling effect reduces the temperature gradient between the two areas, slowing monsoon circulation and resulting in decreased rainfall.
The interplay between greenhouse gases, which warm the ocean and promote more rain, and aerosols, which cool the ocean and lead to less rain, creates a dynamic situation.
Scientists anticipate that, in some years, aerosols may have a greater impact, while in others, the greenhouse effect might prevail.
Considering the dominance of natural aerosols, such as dust, over South Asia during the pre-monsoon period is crucial for understanding climate change in the region.
The incorporation of dust aerosols into climate models, as demonstrated by the U.K. Met Office’s research on African monsoons, is essential for more accurate simulations of the Indian monsoon system.
Similar to studying the effects of carbon dioxide on climate change, a comprehensive approach is necessary to understand how aerosols influence climate.
Developing a system to assess the role of aerosols in determining climate, especially their impact on the complex Indian monsoon, is essential.
While it took over a century to reach a consensus on greenhouse gases and global warming, the hope is that definitive answers to the impact of aerosols can be found more quickly.

FAQs – SMOG, AEROSOL, AND THEIR EFFECT ON MONSOON RAIN

1-What is smog, and how is it formed?

A: Smog is a term derived from “smoke” and “fog.” It results from the combustion of coal, vehicle emissions, and industrial fumes, leading to a hazy atmospheric condition. There are two main types: sulfurous smog and photochemical smog.

2-What is sulfurous smog, and why is it called “London smog”?

A: Sulfurous smog, or “London smog,” is characterized by high levels of sulfur oxides. It is associated with the burning of sulfur-containing fossil fuels, especially coal. The name originates from its initial occurrence in London during the nineteenth century.

3-What causes photochemical smog, known as “Los Angeles smog”?

A: Photochemical smog, or “Los Angeles smog,” results from the reaction of nitrogen oxides and organic compounds, primarily from automobiles, in the presence of sunlight. This type of smog forms ozone, a secondary pollutant.

4-How does smog affect health and visibility?

A: Smog contains toxic gases like ozone, carbon monoxide, and sulfur dioxide, posing health risks such as respiratory issues and reduced visibility due to airborne particulate matter.

5-What role do temperature inversions play in smog formation?

A: Temperature inversions trap pollutants close to the ground, intensifying smog. Inversions occur when warmer air traps cooler air near the surface, reducing atmospheric mixing and worsening pollution.

6-What are aerosols, and how are they formed?

A: Aerosols are tiny particles in the atmosphere. They can be naturally formed, like dust and sea salt, or result from human activities, including the burning of fossil fuels and industrial emissions.

7-How do aerosols influence cloud formation?

A: Naturally formed aerosols act as substrates for water vapor to condense into droplets, aiding cloud formation. However, aerosols from human activities may adversely affect climate.

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Smog (Smoke + Fog), Aerosols and their Impact on Monsoon Rainfall – UPSC Environment Notes