Q.Which of the following is natural and human disturbance in ecology?

PAN (Peroxyacetyl Nitrate) is a secondary pollutant formed in photochemical smog from the reaction of unburnt hydrocarbons and nitrogen oxides in sunlight.

PAN is formed in polluted, sunlit urban air when unburnt hydrocarbons and nitrogen dioxide (from vehicle exhaust) undergo a series of photochemical reactions in the presence of sunlight, along with ozone. It is one of the major components of photochemical smog and is a powerful eye and respiratory irritant, and it damages plants.

SO2, released mainly from burning coal/fuel containing sulphur, irritates the respiratory tract and is linked to bronchitis and other respiratory ailments.

Sulphur dioxide (SO2) is produced when sulphur-containing fossil fuels are burned in power plants, vehicles, and industries. Being an acidic, irritant gas, when inhaled it affects the mucous membranes of the respiratory tract, causing inflammation of the bronchi. Chronic exposure is associated with bronchitis and can aggravate asthma; SO2 is also a major contributor to acid rain.

Acidic pollutant gases (mainly SO2 and NOx) in the air react with the Taj Mahal's marble (calcium carbonate), corroding and yellowing its surface — an effect of air pollution.

The Taj Mahal is built of white marble (largely CaCO3). Air pollutants released by vehicles, industries, and nearby refineries — sulfur dioxide (SO2) and nitrogen oxides (NOx) — combine with moisture in the air to form acids (H2SO4, HNO3), which fall as acid rain or settle as acidic particulates. These acids react with CaCO3:

CaCO3 + H2SO4 → CaSO4 + H2O + CO2

The resulting calcium sulfate is soft, chalky, and yellowish, and it flakes off, eroding the marble and leaving a dull yellow surface. Suspended particulate matter also deposits grime on the surface. This is why a pollution-control buffer zone (the Taj Trapezium Zone) was created around the monument.