Environmental Pollution

1. Requires seismic data from at least three different seismic stations.
2. The distance to the epicenter is calculated using the difference in arrival times of P-waves and S-waves.
3. Each station draws a circle with a radius equal to its calculated distance to the epicenter.
4. The intersection of all three circles determines the location of the epicenter.

Earthquake magnitude quantifies the energy released at the source of the earthquake. Multiple scales exist, with the Richter Scale and the Moment Magnitude Scale (Mw) being among the most widely used.

Richter scale (local magnitude $M_L$)

Originally defined as:

where:

• $A(\Delta)$: Maximum amplitude of the seismic waves at distance $\Delta$.
• $A_0(\Delta)$: Amplitude of a reference event at the same distance.

Empirical adjustment formula (Lillie's formula)

To adjust for distance variations:

where:

• $A$: Amplitude of seismic waves (in micrometers).
• $D$: Distance to the epicenter in kilometers.

Moment magnitude scale ($M_w$)

For large earthquakes, the moment magnitude is preferred and is calculated as:

where $M_0$ is the seismic moment given by:

with:

• $\mu$: Shear modulus of rock (~$3 \times 10^{10} \, \text{Pa}$)
• $A$: Area of fault rupture
• $D$: Average slip on the fault

Magnitude classification table

Pollution refers to the introduction of harmful substances (pollutants) into the environment. These substances can be physical (e.g., heat, radiation), chemical (e.g., gases, metals), or biological.

Types of air pollutants

• Primary Pollutants: Directly emitted from sources (e.g., CO, SO₂).
• Secondary Pollutants: Formed in the atmosphere via chemical reactions (e.g., O₃, smog).

Common pollutants table

Transport of pollutants

• Wind: Affects the horizontal movement of pollutants.
• Atmospheric Stability: Influences vertical dispersion. Unstable atmosphere promotes vertical mixing; stable conditions trap pollutants near the ground.
• Temperature Inversions: Can trap pollutants and cause smog events.

Ground vs. stratospheric ozone

• Ground-level Ozone (Troposphere): Harmful, causes respiratory problems and damages crops. Formed from VOCs + NOₓ in sunlight.
• Stratospheric Ozone: Beneficial, protects life by absorbing harmful ultraviolet (UV) radiation.

Nuclear waste refers to radioactive materials that remain as by-products of nuclear reactions, primarily nuclear fission occurring in nuclear reactors. These materials often include isotopes such as ${}^{141}_{56}\text{Ba}$ (Barium) and ${}^{92}_{36}\text{Kr}$ (Krypton), which are typical fission fragments. Nuclear waste is a subset of a broader category known as radioactive waste.

It is important to differentiate between:

• Nuclear Waste: Produced directly from the fission process in reactors (e.g., spent fuel rods).
• Radioactive Waste: Includes medical and industrial radioactive materials, such as Cobalt-60 used in cancer radiotherapy.

Health effects of radioactive exposure

Radioactive substances affect living organisms through two main types of biological effects:

1. Somatic Effects (Deterministic): These are dose-dependent and appear immediately after exposure to high radiation doses, causing radiation burns, organ damage, or acute radiation syndrome.
2. Stochastic Effects: These occur randomly and are associated with long-term, low-level exposure. Common effects include cancer and genetic mutations. For instance, leukemia and solid cancers may manifest 10–15 years post-exposure.

For a fetus, exposure even to small amounts of radiation can result in birth defects due to rapid cellular division. Prenatal death is also a risk in high exposure scenarios.

Types of nuclear waste

1. Low-Level Waste (LLW): Includes items like contaminated tools, mop heads, gloves, and protective clothing. Typically disposed of in near-surface landfill sites.
2. Intermediate-Level Waste (ILW): Contains higher levels of radioactivity and may require shielding. Includes reactor components and chemical sludge.
3. High-Level Waste (HLW): Primarily spent nuclear fuel or vitrified waste containing long-lived radionuclides. It generates heat and requires deep geological disposal.

Vitrification process

In the vitrification process, HLW is combined with glass-forming additives in a furnace. The molten mixture is poured into stainless steel canisters and solidifies into a stable glass form, minimizing the risk of radioactive leakage.

Figure: Immobilization of High-Level Waste through vitrification and geological burial.

Methods of disposal of nuclear waste

Disposal methods are engineered to ensure containment over geological timeframes:

• Shallow Land Burial: For LLW, under controlled and monitored conditions.
• Deep Geological Repositories: HLW is placed in sealed canisters and buried over 300 meters underground in stable rock formations.

Definition of visibility

Visibility is the greatest distance at which an observer can see and identify a prominent object against the background sky. Atmospheric particles like smoke, dust, and haze reduce visibility by scattering or absorbing incident light.

Light scattering principles

Light scattering occurs when electromagnetic waves interact with particles in the atmosphere. The effectiveness of scattering depends on the particle diameter $d_p$ relative to the wavelength $\lambda$ of incident light.

• If $d_p \ll \lambda$, Rayleigh scattering dominates. Scattering intensity is proportional to:

This explains why shorter wavelengths (e.g., blue light) scatter more than longer ones.

• If $d_p \approx \lambda$, Mie scattering occurs. Common in haze and fog where particles are comparable to visible wavelengths.
• If $d_p \gg \lambda$, particles either absorb or reflect light efficiently, resulting in reduced visibility or darkness (e.g., smoke clouds).

Figure: Scattering of blue light in haze with particles comparable to light wavelength.

Factors affecting visibility

Visibility in the atmosphere is influenced by several physical and chemical factors. These include:

1. Particle size distribution and concentration
   Smaller particles (like aerosols and fine dust) scatter light more efficiently than larger ones, especially when present in high concentrations, reducing the clarity of distant objects.
2. Chemical composition and refractive index
   Chemically reactive particles, such as sulfates or nitrates, have higher light-scattering abilities. Their refractive index determines how much they bend and scatter light, affecting overall visibility.
3. Relative humidity
   High relative humidity causes hygroscopic particles to absorb moisture and grow in size, increasing their ability to scatter and absorb light, which leads to a decrease in visibility.
4. Background light intensity and angle of observation
   Visibility is enhanced in well-lit conditions, but low light or backlighting reduces the ability to see distant objects clearly. The angle at which light enters the eye also changes how particles scatter light, influencing the observer's visual range.

Quantifying visibility impairment

The extinction coefficient $\beta_{ext}$ quantifies light attenuation and is defined as:

where:

• $\beta_{scat}$: Scattering coefficient
• $\beta_{abs}$: Absorption coefficient

The Koschmieder equation relates visibility range $V$ to the extinction coefficient:

(Assuming contrast threshold of 2%)