Air Pollution, Noise and Solid Waste Management

Environmental engineering also covers air quality, noise and solid waste. These topics bring short conceptual and numerical questions in GATE CE.

Air pollutants

• Primary: emitted directly (SO₂, NOₓ, CO, particulate matter PM₁₀ and PM₂.₅, hydrocarbons).
• Secondary: formed in the air (ozone, PAN, sulphuric acid in acid rain). Photochemical smog needs NOₓ, hydrocarbons and sunlight.
• Units: convert ppm (by volume) to µg/m³ at 25 °C and 1 atm: µg/m³ = ppm × M × 1000/24.45 (M = molecular weight in g/mol).
• India's National Ambient Air Quality Standards set limits for each pollutant.

Meteorology

• Dry adiabatic lapse rate: about 9.8 °C/km (temperature drop of rising dry air).
• Environmental lapse rate (ELR) greater than adiabatic: super-adiabatic, unstable (good dispersion; looping plume).
• ELR less than adiabatic: stable (coning plume when neutral to slightly stable; fanning plume in an inversion).
• Inversion (temperature rises with height): very stable, traps pollutants. Fumigation and lofting plumes occur with inversions below or above the stack.
• Gaussian plume model for ground-level concentrations from a stack of effective height H = h + Δh.

Particulate control devices

ESP efficiency (Deutsch–Anderson): η = 1 − e^(−wA/Q).

Noise

• Sound level L = 10 log₁₀(I/I₀) = 20 log₁₀(p/p₀) dB, with p₀ = 20 µPa.
• Adding levels: L_total = 10 log₁₀(Σ 10^(Lᵢ/10)). Two equal sources add 3 dB.
• Equivalent level L_eq averages energy over time. dB(A) weighting follows the ear's response.

Municipal solid waste

• Functional elements: generation, storage, collection, transfer, processing, disposal.
• Processing: composting (aerobic), vermicomposting, anaerobic digestion, incineration (needs high calorific value), recycling.
• Sanitary landfills: liner, leachate collection, gas venting, daily cover.
• Composting needs a C/N ratio of about 25–30.

Practice