Photochemical Smog, AQI and BOD

• Photochemical smog is a brownish haze formed when nitrogen oxides and volatile organic compounds (VOCs) react to sunlight.
• It is more common in summer due to increased sunlight.

Harmful Effects of Photochemical Smog

• Corrodes metals, stones, rubber, and painted surfaces.
• Causes health problems like emphysema, bronchitis, and asthma, especially in senior citizens, children, and people with heart and lung issues.

Air Quality Index (AQI)

• Used to report daily air quality, indicating how clean or polluted the air is and potential health effects.
• Focuses on short-term health effects from breathing polluted air.
• Measured by assessing emissions of eight major pollutants: Particulate Matter (PM2.5 and PM10), Ozone (O3), Carbon Monoxide (CO), Nitrogen Dioxide (NO2), Sulphur Dioxide (SO2), Lead (Pb), and Ammonia (NH3).

Biochemical Oxygen Demand (BOD)

• Represents the amount of dissolved oxygen (DO) consumed by organisms decomposing organic matter in water.
• Indicates water quality inversely; high BOD means low water quality due to less oxygen available for aquatic life.
• The BOD limit for drinking water, according to WHO, is less than 5.0 mg/l to prevent harmful effects.

Chemical Oxygen Demand (COD)

• Measures the amount of oxygen consumed when a water sample is chemically oxidized.
• Used in wastewater treatment plants to measure the oxygen required to break down pollutants.
• High COD indicates more pollutants and decreased dissolved oxygen.
• Industrial units must identify chemicals causing high COD if treated effluent consistently exceeds 250 mg/l before disposal.

Monitoring BOD and COD

• Important for preventing environmental pollution and protecting aquatic life.
• Wastewater sewage should have a BOD around 80 ppm and a COD of 200 ppm for discharge.

Pesticides

• Substances or mixtures used to prevent, destroy, or control pests.
• Includes herbicides, insecticides, nematicides, and fungicides.
• Herbicides are the most commonly used pesticides, accounting for about 50% of global use.
• Can be chemical or biological agents that deter, incapacitate, kill, or discourage pests.

Heavy Metals

• Metals and metalloids with high density that are toxic even at low concentrations.
• Examples include Pb, As, Se, Hg, Cd, Zn, Ag, Cu, Fe, Cr, Ni, Pd, and Pt.
• Released into the environment from industrial discharge, automobile exhaust, and mining.
• Nonbiodegradable and tend to accumulate in living beings, posing a risk as potential carcinogens.
• Long-term exposure can cause various adverse health hazards.

Mercury (Hg)

• A toxic, naturally occurring element.
• Exposure, even in small amounts, can cause serious health problems.
• Exposure routes include skin contact, consuming contaminated fish and breathing mercury vapors.

Cadmium (Cd)

• Highly toxic, exposure can cause cancer.
• Targets cardiovascular, renal, gastrointestinal, neurological, reproductive, and respiratory systems.

Arsenic (As)

• Highly toxic in inorganic form.
• Contaminated water poses the greatest threat to public health.
• Long-term exposure can cause cancer and skin lesions.
• Immediate symptoms of acute poisoning include vomiting, abdominal pain, and diarrhoea and muscle cramping.
• Long-term exposure symptoms include pigmentation changes, skin lesions, and hyperkeratosis.