Photochemical smog is a type of air pollution that occurs when sunlight reacts with pollutants in the atmosphere. It is a significant environmental concern, particularly in urban areas.
Photochemical Smog Components
The primary constituents responsible for the formation of photochemical smog are:
- Oxides of Nitrogen (NOx): Primarily nitrogen monoxide (NO) and nitrogen dioxide (NO$_2$), released from vehicle exhausts and industrial processes.
- Volatile Organic Compounds (VOCs) / Hydrocarbons: Emitted from vehicles, industrial solvents, and vegetation.
- Ozone (O$_3$): Formed when NOx and VOCs react in the presence of sunlight.
These components undergo complex photochemical reactions, leading to the formation of secondary pollutants like ozone, peroxyacetyl nitrate (PAN), and other aldehydes, which cause the characteristic haze and health issues associated with smog.
Analysis of Options
Let's examine why Option D is the correct choice:
- Option 1 (SO$_2$ and NO$_2$): Sulfur dioxide (SO$_2$) is a major component of industrial or London smog, not typically the primary driver of photochemical smog. While NO$_2$ is involved, SO$_2$ is not a key precursor.
- Option 2 (SPM and CO): Suspended Particulate Matter (SPM) and Carbon Monoxide (CO) are significant air pollutants, but they are not the main reactants forming photochemical smog. CO is a product of incomplete combustion, and SPM contributes to haze but isn't a direct precursor in the photochemical reactions.
- Option 3 (SPM and NO$_2$): Similar to Option 2, SPM is not a primary reactant in photochemical smog formation. NO$_2$ is involved, but this option omits crucial components like hydrocarbons and ozone itself.
- Option 4 (Oxides of Nitrogen, Hydrocarbons and Ozone): This option correctly identifies the key precursors (NOx, Hydrocarbons) and a major secondary pollutant (Ozone) that defines photochemical smog.
Therefore, the principal components of photochemical smog are Oxides of Nitrogen, Hydrocarbons, and Ozone.
Important Questions from Environmental Pollution and Control
A tributary flowing at a rate of 4 m3/s converges into a river flowing at a rate of 8.0 m3/s. The concentration of a pollutant 'X' at the upstream of the tributary before convergence was 12 mg/L and that of the river was 30 mg/L. If the pollutant X is completely mixed in the downstream, what would be its concentration?
Consider Gaussian-point source dispersion model with effective stack height H and dispersion coefficient σz = \(\frac{H}{\sqrt2}\). If the effective stack height H increases by 10%, the downwind ground-level concentration of pollutants would
In the two lists given below, List I provides the list of Pollutants, while List II indicates Health Effects. Match the two lists and choose the correct answer from the code given below :
List - I
(Pollutant)
List - II
(Health Effect)
(a) SO2 (i) Nerve and blood effects (b) O 3 (ii) Bronchitis
(c) CO
(iii) Asphyxiant (d) Pb
(iv) Pulmonary injury The online monitoring technique for NOx is based on the Chemiluminiscence of which of the following molecules in excited state?
A 500 MW coal based power station is operating at an efficiency of 30%. If the coal has 1% of sulphur content and 1 tonne of coal produces 8000 kWh energy, how much SO2 will be emitted daily by the plant?
