Pollutants and tropospheric ozone

Primary pollutants from the combustion of fossil fuels include carbon monoxide, carbon dioxide, black carbon or soot, unburned hydrocarbons, oxides of nitrogen, and oxides of sulfur. In the presence of sunlight, secondary pollutants are formed when primary pollutants undergo a variety of reactions with other chemicals already present in the atmosphere. Tropospheric ozone is an example of a secondary pollutant, formed when oxygen molecules react with oxygen atoms that are released from nitrogen dioxide in the presence of sunlight. Tropospheric ozone is highly reactive and damages plants (crops and forests), irritates eyes, creates respiratory illnesses and damages fabrics and rubber materials. Smog is a complex mixture of primary and secondary pollutants, of which tropospheric ozone is the main pollutant.

Photochemical Smog

Photochemical smog occurs when nitrogen oxides (NOx) and volatile organic compounds (VOCs) or primary pollutants react in the presence of sunlight, forming a mixture of harmful secondary pollutants, including ozone (O₃). It commonly occurs in urban areas with heavy traffic and industrial activity, photochemical smog is typically seen as a brownish haze over cities.

Impacts of Photochemical Smog:

• Health: Causes respiratory problems, irritation of the eyes, and aggravates asthma.
• Vegetation: Damages plants by affecting photosynthesis and reducing crop yields.
• Visibility: Reduces visibility and creates the haze commonly associated with smog.

Meteorological and Topographical Factors Affecting Photochemical Smog

• Sunlight:
  • Photochemical smog requires sunlight to catalyze the chemical reactions that produce ozone and other harmful compounds.
• Temperature:
  • Warm temperatures accelerate the formation of ozone, leading to more severe smog conditions.
• Wind:
  • Calm Winds: Allow pollutants to accumulate and form smog.
  • Strong Winds: Can disperse smog, reducing its concentration in one area.