Question

How does urbanization cause air pollution?

Answer 1

1. More vehicles and traffic: Urban growth results in many more cars, buses, and trucks, plus congestion and idling, producing carbon monoxide, nitrogen oxides, hydrocarbons, and particulate matter; vehicular exhaust is a dominant source of urban pollution.
2. Industry and power generation: Factories, refineries, and thermal power plants concentrated near cities burn fossil fuels and emit SO₂, NOx, CO₂, and large amounts of particulates.
3. Household and small-source combustion: In many urban areas, heating, cooking (biomass, coal, oil), and open burning of garbage/stubble release smoke, CO, methane, and particulates that add substantially to urban air loads.
4. Construction, dust, and land‑use change: Building, roadwork, and demolition create dust and airborne particulates; replacing vegetation reduces natural pollutant removal. Wind-blown dust from construction sites and bare soil is a common urban particulate source.
5. Formation of secondary pollutants: Primary emissions (NOx + VOCs) react in sunlight to form ozone and photochemical smog (and PAN), which are often more harmful than the original exhausts. Smog episodes are common in urban areas under sunny, stagnant conditions.
6. Meteorology and urban design effects: Cities create heat islands and “urban canyon” flow patterns that can raise reaction rates and trap pollutants (and winter inversions can hold smoke/fog close to the ground), worsening concentrations and health impacts. Smog and reduced visibility commonly result.