New Insights into Aerosol Chemistry and Air Quality in Extreme Winters

New Insights into Aerosol Chemistry and Air Quality in Extreme Winters

Sub: Env

Sec : Pollution

Why in News

• A recent study by researchers from the University of Alaska Fairbanks and the Georgia Institute of Technology has uncovered a new chemical pathway responsible for worsening air quality during harsh winters.

Contrasting Air Quality: Dras vs. Fairbanks

• Dras (Ladakh, India)
  • Winter temperature: Around -20°C.
  • Air quality: Remarkably clean and healthy.
• Fairbanks (Alaska, USA)
  • Winter temperature: Around -22.4°C.
  • Air quality: Among the worst in the U.S., ranked first in particle pollution (PM).

Particulate Matter (PM):

• PM10-2.5: Particles with diameters between 2.5 and 10 micrometres (μm).
• PM2.5: Ultrafine particles smaller than 2.5 μm, capable of penetrating the lungs and causing severe health issues such as asthma and premature death.
• PM 10 and PM 2.5 are smaller than 10 and 2.5 microns in their diameter, respectively.
• The PM 2.5 particles can easily bypass the nose and throat and can enter the circulatory system.
• The particles can also lead to chronic diseases such as asthma, heart attack, bronchitis and other respiratory problems.
• Byproducts of emissions from factories, vehicular pollution, construction activities and road dust, such particles are not dispersed and stay suspended in the air that we breathe.
• PM2.5 Nonattainment Area: Designation for areas where PM2.5 levels exceed the permissible limit of 35 μg/m³ of air. Fairbanks was declared such an area in 2009 due to emissions from wood stoves, fuel oil burning, industrial sources, and automobiles.

Hydroxymethanesulphonate Formation:

Hydroxymethanesulfonate (HMS) is an organosulfur compound formed through the aqueous-phase reaction between formaldehyde (HCHO) and Sulphur dioxide (SO₂).

This reaction typically occurs in atmospheric water droplets, such as those found in fog or clouds.

Formation Mechanism:

• HMS is produced when formaldehyde reacts with dissolved Sulphur dioxide in the presence of liquid water.
• Elevated relative humidity provides the necessary aqueous medium for the reaction.
• Colder conditions enhance the solubility of gases like SO₂ and HCHO in water droplets, promoting HMS formation.
• Aerosol particles with moderate pH levels facilitate the reaction.

Environmental Impact:

• HMS can constitute a significant fraction of fine particulate matter (PM2.5) in the atmosphere, especially during severe pollution episodes.
• The presence of HMS in aerosols contributes to haze formation and deteriorates air quality, posing health risks.
• As a component of aerosols, HMS influences the Earth’s radiative balance by affecting cloud formation and atmospheric albedo.
• Research in Fairbanks, Alaska, has shown that during winter, lower sulphate concentrations combined with low temperatures lead to less acidic PM particles, increasing HMS production.
• Implications for Emission Controls: Studies suggest that reducing emissions of formaldehyde and other volatile organic compounds may decrease particulate Sulphur levels, indicating a potential co-benefit for air quality management.

Global Significance: HMS has been detected in various regions worldwide, indicating its global relevance in atmospheric chemistry.

Health Considerations: Fine particulate matter containing HMS can penetrate deep into the respiratory tract, potentially leading to adverse health effects.

Aerosol:

• An aerosol is a suspension of fine solid particles or liquid droplets in a gas.
• In the Earth’s atmosphere, aerosols play a crucial role in environmental and climatic processes.
• These particles can originate from natural sources (e.g., volcanic eruptions, sea spray) or human activities (e.g., industrial emissions, vehicle exhaust).

Types of Aerosols

• Natural Aerosols:
  • Dust: Fine particles from soil or deserts, carried by wind.
  • Sea Spray: Salt particles formed when ocean waves break.
  • Volcanic Ash: Tiny particles ejected into the atmosphere during volcanic eruptions.
  • Biogenic Aerosols: Organic particles like pollen, spores, or microbial fragments.
• Anthropogenic (Human-Made) Aerosols:
  • Industrial Emissions: Sulfates, nitrates, and other pollutants released by factories.
  • Combustion Products: Black carbon and organic carbon from vehicle exhaust and biomass burning.
  • Urban Pollution: Aerosols formed due to vehicular traffic and industrial activities.

Role of Aerosols in the Atmosphere

• Radiative Forcing:
  • Cooling Effect: Aerosols like sulfate reflect sunlight back into space, reducing the Earth’s surface temperature.
  • Warming Effect: Black carbon absorbs sunlight, contributing to atmospheric warming.
• Cloud Formation: Aerosols act as cloud condensation nuclei (CCN), enabling water vapor to condense and form clouds.
• Air Quality Impact: High concentrations of aerosols reduce visibility and degrade air quality, posing health risks.
• Impact on Climate: Aerosols influence the global climate by affecting the energy balance of the Earth and modifying cloud properties (indirect effect).