Exercises: Pollution of the fluid layers

Distinguish between a primary pollutant and a secondary pollutant, and give an example of each in the atmosphere.

The diagram summarizes the process of acid rain. Identify the gases marked as 1 and 2 that cause it, explain how it forms from them, and describe its effects on limestone rocks and aquatic ecosystems.

List three sources of pollution of inland waters and classify them as point or non-point sources.

What is smog and what differences are there between classic smog, linked to coal and fog, and the photochemical smog of today's large cities?

Name three effects of air pollution on human health and associate a responsible pollutant with each one.

What is the eutrophication of a lake or an estuary and which nutrients trigger it?

What are heavy metals, such as lead, mercury or cadmium, and why are they a concern even when discharged in low concentrations? Consider their persistence and their bioaccumulation.

What function does the stratospheric ozone layer fulfil and which artificial gases destroyed it? Which international agreement banned them?

Tropospheric ozone is a secondary pollutant formed by photochemical reactions between nitrogen oxides ($\text{NO}_x$) and volatile organic compounds. Explain why its peak levels occur in summer and downwind of major cities.

Biochemical oxygen demand (BOD) measures the organic matter present in water. A discharge of slurry sharply increases the BOD of a river: describe the chain of effects on dissolved oxygen and aquatic life.

Agricultural nitrates pollute many Spanish aquifers. Explain why diffuse pollution is harder to control than a point-source industrial discharge and propose two management measures.

What is the carbon footprint and which greenhouse gases, besides $\text{CO}_2$, does it account for? Give an example of an everyday activity with a high footprint and one with a low footprint.

The acid rain in Scandinavia came partly from emissions from other European countries. Explain the long-range transport of air pollutants and its implications for international cooperation.

Compare the primary, secondary and tertiary treatments of a sewage plant: what each one removes (solids, organic matter, nutrients) and what water quality is obtained after each stage.

What is biomagnification? Trace the concentration of mercury along a marine food chain (phytoplankton, small fish, tuna, humans) and explain its risk.

You can do it on paper and send a photo with your answer.

What do air quality indices measure and how are their alert thresholds used? Explain which actions are triggered in a city when they are exceeded (traffic restriction, warnings to sensitive population).

A popular science article states: "Given that water vapor accounts for more than 60% of the natural greenhouse effect, anthropogenic emissions of $\text{CO}_2$ and $\text{CH}_4$ lack geoclimatic relevance; furthermore, methane degrades in just over a decade, so controlling it is not a priority."

1. a) Refute this argument by justifying why water vapor acts as an internal feedback of the climate system and not as an initial radiative forcing, unlike $\text{CO}_2$.
2. b) Compare the global warming potential (GWP) and the average atmospheric residence time of $\text{CH}_4$ and $\text{CO}_2$. Predict the short-term (20 years) versus long-term (100 years) climatic consequences if methane mitigation were prioritized exclusively.
3. c) Select a currently observable geological consequence linked to global temperature rise (in the cryosphere or in coastal dynamics), explain its physical mechanism, and indicate which field indicator allows it to be measured.

In an intramontane basin where an industrial city is located, the following air temperature data are recorded at 07:00 h on a clear winter day:

• Ground level (600 m): 1,0 °C

• 800 m: -1,0 °C

• 1 000 m: 6,0 °C

• 1 300 m: 3,5 °C

• 1 600 m: 0,5 °C

An industrial chimney located at 600 m emits flue gas at an altitude of 1 050 m with an exit temperature of 4,0 °C.

1. a) Identify the exact altitudinal interval where a thermal inversion exists, calculate the vertical temperature gradient in that interval, and explain the meteorological and topographic mechanism that generated it overnight.
2. b) Predict with reasoned arguments the dynamic behavior of the plume emitted at 1 050 m: will it rise freely, descend toward the valley floor, or remain trapped in neutral buoyancy? Justify it by comparing the density and temperature of the plume with those of the surrounding air.
3. c) If from midday onwards insolation raises the ground temperature to 12,0 °C, predict what will happen to the vertical structure of the atmosphere and how the concentration of pollutants at street level will evolve during the breakup of the inversion.

High concentrations of synthetic microfibers (polyester, average density $\approx 1,38\text{ g/cm}^3$) have been found both in ultra-deep ocean trench sediments (> 8 000 m) and floating in the sea surface microlayer.

1. a) Resolve the apparent physical paradox: if polyester is significantly denser than surface seawater ($\approx 1,025\text{ g/cm}^3$), what hydrodynamic and biological processes (such as surface tension, biofouling, and "marine snow") explain both its prolonged initial buoyancy and its accelerated transport to the abyssal sea floor?
2. b) If a conventional wastewater treatment plant (WWTP) retains up to 95% of these microfibers from textile washing in its primary and secondary sludge, justify why this does not solve the environmental problem if such sludge is reused as agricultural fertilizer.
3. c) Design two viable preventive or corrective barriers: one technological, applicable in the urban hydrological cycle, and another at the level of textile materials science, evaluating their potential technical limitations.

Consider the inorganic carbon equilibrium system in seawater:

(1) $\text{CO}_2\text{ (g)} \rightleftharpoons \text{CO}_2\text{ (aq)}$

(2) $\text{CO}_2\text{ (aq)} + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{H}^+ + \text{HCO}_3^-$

(3) $\text{H}^+ + \text{CO}_3^{2-} \rightleftharpoons \text{HCO}_3^-$

(4) $\text{Ca}^{2+} + \text{CO}_3^{2-} \rightleftharpoons \text{CaCO}_3\text{ (s)}$

1. a) If the burning of fossil fuels massively injects $\text{CO}_2$ into the atmosphere, apply Le Chatelier's principle to predict how each equilibrium shifts. Justify why the concentration of the carbonate ion ($\text{CO}_3^{2-}$) decreases, even though the total amount of dissolved carbon in the ocean increases.
2. b) Relate the reduction of $\text{CO}_3^{2-}$ to the solubility product of calcium carbonate and the saturation state ($\Omega$) of calcite and aragonite. Predict the consequences for the calcite compensation depth (CCD) and for the preservation of fossils and benthic shells.
3. c) To combat this problem, "enhanced weathering" geoengineering has been proposed through the controlled addition of basic minerals (such as finely ground olivine) in coastal areas. Justify its foundation geochemically and point out two associated ecological risks.

Following a torrential rain event associated with a DANA (isolated cut-off low) in an agricultural basin, millions of cubic meters of fresh water loaded with nitrates and phosphates enter a shallow coastal lagoon. Three weeks later, dissolved oxygen at the bottom drops to 0,1 mg/L, with almost total anoxia and massive mortality of fish and bivalves, while in the top 30 cm of the water column, oxygen stands at 8,0 mg/L.

1. a) Justify the formation of a pycnocline (combined gradient of salinity and temperature) after the torrential flood and explain physically why it prevents bottom reoxygenation by atmospheric diffusion or mechanical mixing by moderate wind.
2. b) Describe the biogeochemical cascade that triggers the proliferation and subsequent collapse of phytoplankton, detailing the bacterial degradation of biomass at the bottom and the massive release of phosphorus from sediments under anoxic conditions (positive feedback loop).
3. c) Critically evaluate two alternative interventions: widening and dredging the connection channels with the open sea versus constructing a perimeter belt of constructed wetlands and woodchip bioreactors to treat groundwater and runoff. Justify which one is environmentally sustainable and which one could irreversibly alter the ecological nature of the lagoon.

In global carbon budget models, it is assumed that oceans and forest masses will continue to absorb around 50% of net anthropogenic emissions. However, various biogeochemists warn of the instability of these sinks in the face of global change.

1. a) Using Henry's law and changes in ocean stratification, predict how surface thermal warming and the slowdown of the thermohaline circulation (AMOC) will affect the solubility pump and the marine biological pump.
2. b) In boreal and temperate forest ecosystems, analyze how increasing summer temperatures and water stress interact on the ratio between net photosynthesis and soil heterotrophic respiration. Under what circumstances can a mature forest transform from a net sink into a net source of $\text{CO}_2$?
3. c) A commercial airline offers "carbon neutral" tickets by investing part of the fare in single-species plantations of fast-growing trees on grassland areas. Demonstrate the geological and temporal asymmetry of this offset, refuting that a labile biological reservoir is equivalent to the permanent geological confinement of extracted fossil fuels.

A conventional thermal power plant discharges its cooling water into a river whose low-flow discharge is 15,0 m³/s. The discharge increases the average temperature of the receiving reach from 18,0 °C to 28,0 °C. Upstream of the discharge, the river also receives secondary effluent from an urban wastewater treatment plant with a residual $\text{BOD}_5$ of 20,0 mg/L.

1. a) Explain the combined lethal impact on native fish fauna through two opposing factors: the thermodynamics of dissolved gas (the saturation curve of $\text{O}_2$ in water) and the metabolic $Q_{10}$ law (according to which the basal metabolism and oxygen demand of poikilothermic organisms doubles for every 10 °C thermal increase).
2. b) Mentally draw or describe in a reasoned manner the dissolved oxygen sag and recovery curve (Streeter-Phelps curve) downstream of the thermal discharge compared to the one that would be observed at 18,0 °C. Specify what happens to the rate of biological degradation of organic matter and to the position of the critical oxygen deficit point.
3. c) Compare technically and environmentally two mitigating measures at the power plant: installing evaporative closed-circuit cooling towers versus constructing shallow retention and natural cooling ponds prior to river discharge. Evaluate the consumptive water use and the impact on the local microclimate of both.

Persistent organic pollutants (POPs), such as hexachlorobenzene (HCB) and polychlorinated biphenyls (PCBs), show concentrations a thousand times higher in the adipose tissue of polar bears and Arctic cetaceans than in the phytoplankton of polar seas, even though there are no industrial sources emitting them at those latitudes.

1. a) Explain the process of global fractional distillation ("grasshopper effect"): justify how latitudinal temperature variations, together with the vapor pressure and hydrophobicity of each substance, determine which pollutants reach polar areas and which are deposited at temperate latitudes.
2. b) Justify, through the physicochemical properties of the compound (in particular the octanol-water partition coefficient, $\log K_{ow} > 5$) and the structure of Arctic food webs, why these compounds biomagnify so sharply at higher trophic levels, clearly distinguishing biomagnification from bioconcentration.
3. c) In recent decades it has been confirmed that permafrost thawing and the reduction of summer Arctic sea ice are causing local increases in DDT and lindane concentrations in polar surface water, decades after their ban by the Stockholm Convention. Propose two geochemical hypotheses explaining how global warming turns Arctic cryospheric reservoirs from secondary sinks into new active sources of POPs.

Unit challenge. Environmental assessment of an atmospheric and hydrological dispersion event.

Imagine that you advise the environmental department of your municipality. Analyze how recent atmospheric dynamics have conditioned air and water quality in your surroundings:

1. Data collection: Consult AEMET and the MITECO air quality viewer for records from your nearest station over the last 5 days: surface pressure ($hPa$), wind speed ($m/s$), precipitation ($mm$), and levels of $PM_{10}$ or $NO_2$ ($\mu g/m^3$).

2. Dynamics and dispersion: Prepare a comparative table and reason whether anticyclonic conditions or a thermal inversion in the troposphere have favored the confinement of pollutants compared to cyclonic situations with greater convective mixing.

3. Interaction with the hydrosphere: Evaluate how atmospheric scavenging by precipitation (with possible $pH < 5,6$) or urban runoff transfers this pollutant load to a nearby river or aquifer, altering parameters such as turbidity or dissolved oxygen.

4. Action proposal: Design a one-page executive summary with two contingency measures based on weather forecasting to mitigate emission peaks.

Assessment criteria:

• Conceptual accuracy in integrating tropospheric dynamics with pollutant transport.

• Coherence in explaining mass transfer between the atmosphere and hydrosphere.

• Rigorous use and graphical treatment of the official data obtained.