10.2 Air, Water, Soil & Noise Pollution and Health Impacts

Air, Water, Soil & Noise Pollution and Health Impacts

Quick Answer: Environmental pollutants are classified by origin, physical state, and receptor medium. Air pollutants divide into primary (emitted directly: $CO, SO_2, NO_x$, primary PM) and secondary (formed in the atmosphere: $O_3, PAN, H_2SO_4$). India's National Air Quality Index (AQI) tracks 8 criteria pollutants ($PM_{2.5}, PM_{10}, SO_2, NO_2, CO, O_3, NH_3, Pb$) across 6 color tiers. Photochemical smog is oxidizing (summer, $NO_x$ + VOCs + UV), while Classical smog is reducing (winter, smoke + fog + $SO_2$). Water pollution is quantified by Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), and Chemical Oxygen Demand (COD). Major heavy metal pathologies include Arsenic (Blackfoot disease), Cadmium (Itai-Itai), Mercury (Minamata), Lead (Plumbism), and Fluoride (Fluorosis).

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1. Atmospheric Pollution: Primary vs. Secondary Pollutants

Air pollution involves the introduction of particulates, biological molecules, or toxic gases into Earth's atmosphere, causing disease, death to humans, damage to other living organisms, or degradation of natural and built environments.

                     ┌─────────────────────────────────────────┐
                     │       CLASSIFICATION OF POLLUTANTS      │
                     └────────────────────┬────────────────────┘
                   ┌──────────────────────┴──────────────────────┐
                   ▼                                             ▼
        ┌───────────────────────┐                     ┌───────────────────────┐
        │   PRIMARY POLLUTANTS  │                     │  SECONDARY POLLUTANTS │
        │ • Emitted Directly    │   Chemical / Solar  │ • Formed in Ambient   │
        │ • CO, SO2, NO, NO2    │ ──────────────────> │   Atmosphere          │
        │ • Primary PM2.5/PM10  │     Transformations │ • O3, PAN, H2SO4 Mist │
        │ • NH3, Pb, VOCs       │                     │ • Photochemical Smog  │
        └───────────────────────┘                     └───────────────────────┘

Primary Pollutants

Substances emitted directly from identifiable sources (anthropogenic or natural) into the ambient air in a harmful form:

• Carbon Monoxide ($CO$): Colorless, odorless gas produced by incomplete combustion of carbon-containing fuels (automobiles, biomass, coal). Binds with blood hemoglobin to form carboxyhemoglobin ($COHb$) with an affinity $\sim 200\text{--}250\text{ times}$ greater than oxygen, causing tissue hypoxia, neurological impairment, and asphyxiation.
• Sulfur Dioxide ($SO_2$): Pungent gas released from coal/oil combustion in thermal power plants and metal smelting. Causes bronchoconstriction, aggravates asthma, and acts as the chief precursor to sulfuric acid rain.
• Nitrogen Oxides ($NO_x = NO + NO_2$): Produced during high-temperature vehicular and industrial combustion when atmospheric $N_2$ and $O_2$ react. Induces pulmonary edema, bronchitis, and serves as a vital precursor for both acid rain and ground-level ozone.
• Particulate Matter ($PM_{10}$ & $PM_{2.5}$): Solid particles and liquid droplets suspended in air. $PM_{10}$ (inhalable particles $\le 10,\mu\text{m}$) deposits in the upper respiratory tract; $PM_{2.5}$ (fine respirable particles $\le 2.5,\mu\text{m}$) penetrates deep into lung alveoli and crosses the air-blood barrier, inducing cardiovascular and respiratory morbidity.
• Ammonia ($NH_3$): Emitted from agricultural fertilizer application and livestock manure. Reacts with acidic air pollutants to form secondary ammonium aerosols.
• Lead ($Pb$): Heavy metal emitted from legacy leaded fuels, battery manufacturing, smelters, and paints. Accumulates in bones, causing severe neurotoxicity, learning disabilities in children, and renal dysfunction.

Secondary Pollutants

Pollutants not emitted directly; synthesized when primary pollutants undergo chemical reactions or photochemical transformations in the presence of sunlight and atmospheric moisture:

• Tropospheric / Ground-level Ozone ($O_3$): Formed by photochemical reactions between $NO_x$ and Volatile Organic Compounds (VOCs) under solar UV radiation. A potent oxidizing agent causing deep lung irritation, coughing, reduced crop yields, and rubber degradation.
• Peroxyacetyl Nitrate (PAN: $CH_3COOONO_2$): A powerful eye irritant (lachrymator) and plant toxicant formed alongside ozone in photochemical smog.
• Acid Mists ($H_2SO_4$ & $HNO_3$): Formed when $SO_2$ and $NO_2$ are oxidized by hydroxyl radicals ($OH^\bullet$) and dissolved in atmospheric water droplets.

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2. National Air Quality Index (AQI) Architecture

Launched by the Ministry of Environment, Forest and Climate Change (MoEFCC) and Central Pollution Control Board (CPCB) under the Swachh Bharat Abhiyan in October 2014, the National AQI transforms complex chemical concentration data of multiple pollutants into a single numerical index, color code, and descriptive health category ("One Number-One Colour-One Description").

Criteria Pollutants Monitored

The AQI is calculated based on 8 criteria air pollutants:

1. Particulate Matter $\le 10,\mu\text{m}$ ($PM_{10}$, 24-hr avg)
2. Particulate Matter $\le 2.5,\mu\text{m}$ ($PM_{2.5}$, 24-hr avg)
3. Nitrogen Dioxide ($NO_2$, 24-hr avg)
4. Sulfur Dioxide ($SO_2$, 24-hr avg)
5. Carbon Monoxide ($CO$, 8-hr avg in $\text{mg/m}^3$)
6. Ozone ($O_3$, 8-hr avg)
7. Ammonia ($NH_3$, 24-hr avg)
8. Lead ($Pb$, 24-hr avg)

[!IMPORTANT] An overall AQI can only be calculated if data is available for a minimum of three pollutants, out of which one must necessarily be either $PM_{2.5}$ or $PM_{10}$.

National AQI Categories, Breakpoints & Health Impacts

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3. Smog Chemistry: Photochemical vs. Classical (London) Smog

Smog (a portmanteau of "smoke" and "fog") manifests in two chemically and meteorologically distinct forms:

┌─────────────────────────────────────────────────────────────────────────────┐
│                            COMPARATIVE SMOG PROFILES                        │
├──────────────────────────────────────┬──────────────────────────────────────┤
│    PHOTOCHEMICAL (LOS ANGELES) SMOG   │        CLASSICAL (LONDON) SMOG       │
├──────────────────────────────────────┼──────────────────────────────────────┤
│ • Season/Climate: Warm, Sunny Summer │ • Season/Climate: Cool, Humid Winter │
│ • Nature: OXIDIZING                  │ • Nature: REDUCING                   │
│ • Primary Drivers: NOx + VOCs + UV   │ • Primary Drivers: Coal Smoke + SO2  │
│ • Key Products: O3, PAN, Aldehydes   │ • Key Products: H2SO4 Mist, Soot     │
│ • Visual Color: Brownish Haze (NO2)  │ • Visual Color: Dark Grey/Black Fog  │
└──────────────────────────────────────┴──────────────────────────────────────┘

Detailed Chemical Mechanisms

• Photochemical Smog:
  1. $NO_2 + h\nu (\text{UV solar radiation}) \rightarrow NO + O(^3P)$ (Atomic Oxygen)
  2. $O(^3P) + O_2 + M \rightarrow O_3 + M$ (Tropospheric Ozone Synthesis)
  3. $O_3 + NO \rightarrow NO_2 + O_2$ (Normal scavenge cycle; disrupted by hydrocarbons)
  4. $\text{VOCs} + OH^\bullet \rightarrow R^\bullet + H_2O \xrightarrow{O_2} RO_2^\bullet$ (Peroxy Radicals)
  5. $RO_2^\bullet + NO \rightarrow RO^\bullet + NO_2$ (Oxidizes $NO$ without consuming $O_3$, causing runaway $O_3$ accumulation)
  6. $RCO_3^\bullet + NO_2 \rightarrow RCO_3NO_2$ (Peroxyacetyl Nitrate - PAN)
• Classical Smog:
  1. Heavy combustion of sulfur-laden coal produces high ambient concentrations of soot and $SO_2$.
  2. Under winter temperature inversion (trapping cold surface air under warm air) and high humidity, $SO_2$ dissolves in fog droplets: $SO_2 + H_2O \rightarrow H_2SO_3 \xrightarrow{O_2, \text{catalyst (soot/metals)}} H_2SO_4$
  3. The resulting reducing aerosol induces severe pulmonary edema (e.g., London Great Smog of December 1952, causing $\sim 12,000$ fatalities).

4. Acid Rain Kinetics and Material Degradation

Normal, unpolluted precipitation is naturally slightly acidic with a pH of approximately 5.6 due to the atmospheric dissolution of carbon dioxide forming weak carbonic acid:

$CO_2(g) + H_2O(l) \rightleftharpoons H_2CO_3(aq) \rightleftharpoons H^+(aq) + HCO_3^-(aq)$

Acid Precipitation is defined as precipitation (rain, snow, fog, dew) exhibiting a $\text{pH} < 5.6$, driven by anthropogenic emissions of sulfur dioxide ($SO_2$) and nitrogen oxides ($NO_x$):

• Sulfuric Acid Contribution (60–70%): $SO_2 \xrightarrow{OH^\bullet, O_2, H_2O} H_2SO_4$
• Nitric Acid Contribution (30–35%): $NO_2 + OH^\bullet \rightarrow HNO_3$

Ecological & Material Impacts

1. Soil Cation Leaching: Acid rain leaches vital plant nutrients ($Ca^{2+}, Mg^{2+}, K^+$) from topsoil while mobilizing toxic aluminum ions ($Al^{3+}$) from soil minerals into root zones and waterways, damaging plant roots and aquatic fish gills.
2. Marble Cancer / Stone Leprosy: Acid deposition degrades historical calcium carbonate (limestone/marble) structures, such as the Taj Mahal in Agra (impacted by emissions from Mathura Refinery):

$\text{CaCO}_3(\text{marble}) + \text{H}_2\text{SO}_4(\text{acid rain}) \rightarrow \text{CaSO}_4\cdot 2\text{H}_2\text{O}(\text{gypsum}) + \text{CO}_2 \uparrow$

Gypsum is highly water-soluble and mechanically brittle, causing structural pitting, black crust formation, and severe surface spalling.

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5. Water Quality Parameters: DO, BOD, COD & Heavy Metal Pathologies

Quantitative Water Quality Metrics

• Dissolved Oxygen (DO): The concentration of free, non-compound $O_2$ dissolved in water. Pristine freshwater contains $8\text{--}10\text{ mg/L}$ of DO at $20^\circ\text{C}$. A drop below $4\text{--}5\text{ mg/L}$ indicates severe pollution and induces aquatic mortality.
• Biochemical Oxygen Demand (BOD): The quantity of dissolved oxygen required by aerobic microorganisms to biologically oxidize the biodegradable organic matter present in a water sample over a 5-day incubation period at $20^\circ\text{C}$ ($ ext{BOD}_5$).
  • Clean drinking water: $\text{BOD} < 1\text{ mg/L}$
  • Moderately polluted river: $\text{BOD} = 2\text{--}8\text{ mg/L}$
  • Raw municipal sewage: $\text{BOD} = 150\text{--}350\text{ mg/L}$
  • Untreated industrial effluent: $\text{BOD} > 1,000\text{ mg/L}$
• Chemical Oxygen Demand (COD): The total quantity of oxygen required to chemically oxidize both biodegradable and non-biodegradable organic compounds using a boiling mixture of a powerful chemical oxidizing agent (potassium dichromate, $K_2Cr_2O_7$) in concentrated sulfuric acid ($H_2SO_4$).

$\text{COD} > \text{BOD} \quad \text{(Always, as COD encompasses total oxidizable carbon)}$ $\text{Biodegradability Index} = \frac{\text{BOD}_5}{\text{COD}} \quad (\text{Ratios } > 0.5 \text{ indicate readily biodegradable domestic waste})$

Heavy Metal and Inorganic Chemical Pathologies

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6. Soil Contamination, Biomagnification & Ambient Noise Standards

Bioaccumulation vs. Biomagnification

• Bioaccumulation: The progressive increase in contaminant concentration within an individual organism over its lifespan because the rate of absorption exceeds metabolic excretion.
• Biomagnification: The progressive increase in toxicant concentration at successively higher trophic levels in a food chain. Classic example: Persistent Organic Pollutants (POPs) like DDT and PCBs, which are lipophilic and resistant to environmental degradation, concentrating from water ($0.000003\text{ ppm}$) to zooplankton ($0.04\text{ ppm}$) to small fish ($0.5\text{ ppm}$) to fish-eating predatory birds ($25\text{ ppm}$), resulting in eggshell thinning and population collapse.

CPCB Ambient Noise Pollution Standards

Noise is legally defined as an air pollutant under the Air (Prevention and Control of Pollution) Act 1981 (amended 1987). Ambient noise limits are regulated by the Noise Pollution (Regulation and Control) Rules, 2000 in $L_{\text{eq}},\text{dB(A)}$:

[!NOTE] A Silence Zone comprises an area within a 100-meter radius around hospitals, educational institutions, courts, and religious establishments, officially declared by competent authorities.