Nitrogen and Sulfur Oxides: Impacts on Environment and Health

Nitrogen Oxides (NOx): Environmental and Health Impacts

There are eight distinct nitrogen oxides (NOx), but only three are commonly found in the atmosphere:

• Nitrous oxide (N₂O): Emitted naturally, non-toxic, and not considered an air pollutant.
• Nitrogen monoxide (NO): A toxic, colorless, and odorless gas primarily from natural sources, with a smaller contribution from anthropogenic sources.
• Nitrogen dioxide (NO₂): A toxic, reddish-brown gas with a strong, suffocating odor, almost entirely of anthropogenic origin.

Effects of Nitrogen Oxides

The danger of nitrogen oxide contamination to plants and animals is more potential than actual, given current atmospheric levels. Of these oxides, NO₂ is the most toxic to humans, affecting the respiratory system and potentially being lethal. Regarding materials, it affects textile dyes and contributes to corrosion in metallic structures.

Sulfur Dioxide (SO₂): A Major Air Pollutant

Most sulfur oxides emitted into the atmosphere are in the form of sulfur dioxide (SO₂).

Effects of Sulfur Dioxide

SO₂ undergoes photooxidation to form sulfuric acid (H₂SO₄), a component of sulfurous smog. Dissolved H₂SO₄ in water droplets returns to the surface as acid rain, causing considerable damage. SO₂ also causes lesions on plant leaves, affecting photosynthetic activity. In humans, SO₂ primarily affects the respiratory system, though higher concentrations are needed to cause damage compared to plants. It can also irritate mucous membranes, such as those in the eyes. This pollutant contributes to the cracking of paint and the deterioration of leather and paper. Lichens are highly sensitive to SO₂, even at low concentrations, making them useful biomarkers for this type of contamination.

Hydrocarbons (C_xH_y): Formation of Photochemical Smog

Hydrocarbons (C_xH_y) comprise a complex and broad group of organic contaminants, both natural and anthropogenic.

Effects of Hydrocarbons

The primary concern with hydrocarbons is their role in the formation of ozone (O₃). This occurs in the presence of sunlight and low relative humidity, leading to a complex cloud of smoke known as photochemical smog, as seen in Los Angeles. This oxidizing, acidic smog is increasingly common in large, brightly lit cities. Photochemical oxidants like O₃, peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), and peroxybenzoyl nitrate (PBzN) cause irritation of the nose, throat, and eyes, and can even lead to extreme fatigue and lack of coordination. Regarding materials, O₃ affects vehicle tires, pulp tissue, and binders in paints.

The Hydrological Cycle: Earth's Water in Constant Motion

The volume of water on Earth remains constant, even as it moves and changes its physical state. This is due to the hydrological cycle, which connects the hydrosphere, atmosphere, geosphere, and biosphere.

Phases of the Water Cycle

• Internal Cycle

  Driven by heat and density differences within the Earth. Water of magmatic origin, known as juvenile water, is formed by chemical reactions inside the Earth. It emerges through volcanoes, ridges, or deep fractures and mixes with the waters of the external cycle.

• External Cycle

  Powered by solar energy, which causes evaporation and evapotranspiration, and gravity, which causes precipitation, infiltration, and runoff. Part of this phase occurs in the atmosphere, and another part on the surface or at shallow depths. Clouds transport water vapor until precipitation occurs as rain, snow, or hail. Some water is deposited as surface runoff, while another part infiltrates the ground, forming groundwater and aquifers. This water can be used by living organisms or flow to the sea. Surface water returns to the atmosphere through evaporation and evapotranspiration from the environment and living organisms. This generates clouds through condensation, which are then moved, closing the cycle.

Purpose of the Hydrological Cycle

The hydrological cycle is crucial for regulating Earth's surface temperature, transporting matter and energy, causing rock erosion, and transferring and discharging sediments on continents regularly.