Exercises: The atmosphere

Name the layers of the atmosphere in order from Earth's surface outwards into space and state a characteristic feature of each.

State the main composition of air (the two dominant gases with their approximate proportions) and name two trace gases whose variation is of major environmental importance.

In which layer of the atmosphere do weather phenomena occur and in which is ozone concentrated? Explain the function of each of these two layers.

Explain what atmospheric pressure is, with which instrument it is measured and in which units, and discuss how and why it varies with altitude (what does a barometric altimeter actually measure?).

What is the relative humidity of the air? Explain why the same amount of water vapour gives different relative humidity values depending on the temperature, and relate it to the formation of dew as the night cools.

Explain why the sky looks blue at midday and reddish at sunset, resorting to the scattering of light by the molecules of the air and to the longer path the light travels when the Sun is low.

Name four primary atmospheric pollutants (sulphur dioxide, nitrogen oxides, suspended particles, carbon monoxide) and indicate one main source of each.

What is the tropopause and at what approximate altitude is it located? Discuss why commercial aircraft fly close to it (stability, less turbulence, lower consumption).

Explain what the lapse rate (vertical thermal gradient) of the troposphere is and what a thermal inversion is, relating the latter to episodes of trapped pollution over major cities in winter.

Describe the function of the stratospheric ozone layer, what substances destroyed it (CFCs), and why the Montreal Protocol is considered the greatest success of environmental diplomacy.

Outline in words the general circulation of the atmosphere (Hadley cell, Intertropical Convergence Zone, subtropical anticyclones) and use it to explain the climatic contrast between the humid north and the arid south-east of the Iberian Peninsula.

Explain the mechanism of the daytime sea breeze and of the night-time land breeze (differential warming and cooling of land and sea) and discuss what effect they have on the pollution of a coastal city (do they carry it out to sea or recirculate it?).

Explain the Foehn effect: what happens to a mass of humid air as it climbs a mountain range (cooling, condensation, rain) and as it descends on the other slope (drier and warmer air), and relate it to the contrast between the Cantabrian coast and the Meseta.

Distinguish between a warm front and a cold front: which air mass advances in each case, which clouds and what type of precipitation (persistent or intense and brief) each brings, and what temperature change an observer notices after they pass.

Distinguish between classical or London-type smog (a mixture of smoke and fog with $\text{SO}_2$ and particles) and Los Angeles-type photochemical smog (ozone and secondary compounds formed by sunlight), indicating the season and the typical conditions of each.

Explain the role of the Azores anticyclone in the summer climate of the Peninsula (stable, dry weather) and that of the trade winds in the Canaries, including the formation of the "sea of clouds" that waters the laurel forests.

Based on the thermal profile recorded by a probe in the Earth's atmosphere (zones 1 to 4):

1. a) Justify, using the concepts of air density and lapse rate, why zone 2 acts as a dynamic lid that prevents the vertical development of storm clouds from zone 1.
2. b) Predict how the morphology of the thermal curve in zone 2 would change if the ozone layer were completely destroyed, and what direct consequence that change would have on the altitude of the upper boundary of zone 1.
3. c) Commercial flights frequently choose the transition level between zones 1 and 2, whereas auroras are only observed in zone 4. Justify the commercial flight altitude based on atmospheric stability and fuel consumption, and explain why auroras cannot occur at lower altitudes.

Consider Earth's radiation budget in initial equilibrium (average incident $340\ \text{W/m}^2$ at the top of the atmosphere).

1. a) A climate model evaluates two independent anthropogenic disturbances: 1) a reduction in mean albedo from $30\ \%$ to $28\ \%$ due to Arctic ice melt and urbanization; 2) an increase in greenhouse gases that decreases the outgoing longwave radiation emitted to outer space by $3{,}5\ \text{W/m}^2$. Calculate the net radiative forcing introduced by each disturbance and interpret which one would cause a greater initial thermal imbalance.
2. b) A climate change denier argues: "If Earth absorbs more energy than it emits, the surface will immediately emit more infrared radiation into space and equilibrium will be restored without an increase in mean temperature." Reasonably refute this claim using the Stefan-Boltzmann law and the absorption/re-emission mechanism of the greenhouse effect.
3. c) Explain how radiometers aboard satellites (such as the CERES mission) manage to measure Earth's energy imbalance by distinguishing reflected shortwave energy from emitted thermal longwave radiation.

During a winter episode in a large inland city like Madrid, a monitoring station records an $\text{NO}_2$ concentration of $240\ \mu\text{g/m}^3$ at 7:00 AM (above the pre-alert threshold) and high levels of $\text{PM}_{2{,}5}$. The radiosonde shows a surface temperature of $-1{,}5\ \text{°C}$ and $+4{,}5\ \text{°C}$ at an altitude of $300\ \text{m}$, with surface winds of $0{,}4\ \text{m/s}$.

1. a) Demonstrate with the thermal data why pollutants cannot disperse vertically, calculating the vertical lapse rate of that layer in $\text{°C/100 m}$ and deducing its sign relative to the normal adiabatic lapse rate.
2. b) Critically evaluate two emergency measures of the pollution protocol: banning parking for non-residents in the city center versus reducing the speed limit on ring roads to $70\ \text{km/h}$. Justify which one acts more directly on $\text{NO}_2$ emissions associated with braking, acceleration, and vehicular congestion.
3. c) Design two structural urban planning and mobility measures that permanently reduce the city's vulnerability to these meteorological episodes, justifying their feasibility in terms of the emissions budget.

In January, a station at the bottom of the Ebro basin ($130\ \text{m}$ altitude) records dense fog for ten consecutive days with maximum temperatures of $1{,}5\ \text{°C}$, while an observatory on a surrounding plateau ($850\ \text{m}$) records clear skies and $14\ \text{°C}$ at 2:00 PM.

1. a) Interpret the thermodynamic origin of this situation: justify how nocturnal radiative cooling in a basin-like topography and subsidence from a winter anticyclone interact to generate an extraordinarily persistent basal thermal inversion.
2. b) Explain the positive feedback loop whereby the albedo of the fog itself prevents daytime insolation from warming the ground, perpetuating the trapping of the cold air mass and pollutants at the valley floor.
3. c) Predict what will happen to the particulate matter concentration in the valley if anticyclonic subsidence intensifies versus a scenario in which an Atlantic front with northwesterly winds (cierzo) exceeding $45\ \text{km/h}$ enters the region. Justify the evolution of atmospheric stability in both cases.

Despite more than $80\ \%$ of historical CFC emissions originating in the Northern Hemisphere, the ozone hole is much deeper and more recurrent over Antarctica than over the Arctic.

1. a) Resolve this apparent geographical paradox: relate the distribution of continental and marine masses at both poles to the strength of the polar vortex, and justify why temperatures below $-78\ \text{°C}$ in the austral stratosphere promote the massive formation of polar stratospheric clouds (PSCs), which are absent in the Arctic in most years.
2. b) During the polar night, chlorine remains trapped in inactive reservoir compounds (such as $\text{ClONO}_2$ and $\text{HCl}$). Explain the heterogeneous reaction that occurs on the ice crystals of PSCs and justify why explosive ozone destruction takes place precisely at the beginning of the austral spring (September–October) and not in the middle of winter.
3. c) If CFC emissions were drastically reduced following the Montreal Protocol, justify, based on the chemical kinetics of CFCs and stratospheric transport dynamics, why the average recovery time of the ozone column is measured in decades rather than years.

An atmospheric sounding taken over a plain at midday records $28\ \text{°C}$ at $0\ \text{m}$ altitude; $19\ \text{°C}$ at $1000\ \text{m}$; $14\ \text{°C}$ at $2000\ \text{m}$; $11\ \text{°C}$ at $3000\ \text{m}$; and $-56\ \text{°C}$ at $12\ \text{km}$ (tropopause level).

1. a) Calculate the environmental vertical temperature gradient (environmental lapse rate, ELR) in $\text{°C/100 m}$ for each of the first three sections ($0-1000\ \text{m}$, $1000-2000\ \text{m}$, and $2000-3000\ \text{m}$) and compare them with the standard average tropospheric lapse rate ($0{,}65\ \text{°C/100 m}$).
2. b) A parcel of dry air at $30\ \text{°C}$ rises due to thermal buoyancy, cooling at the dry adiabatic lapse rate ($\text{DALR} = 1\ \text{°C/100 m}$). Determine the exact altitude at which it will reach neutral buoyancy and state whether the atmosphere is unstable or stable in each of the sections it traverses.
3. c) Predict what will happen to the buoyancy of a storm cloud rising with convective force when its top reaches $12\ \text{km}$ and penetrates into the stratosphere. Based on this, justify why cumulonimbus clouds develop a flat, anvil-shaped morphology at that level.

Long-range atmospheric transport connects regions separated by thousands of kilometers, such as Saharan dust masses reaching the Iberian Peninsula or industrial $\text{SO}_2$ emissions from Central Europe acidifying Scandinavian lakes.

1. a) Interpret the following biogeochemical paradox: a severe Saharan dust intrusion dangerously increases airborne particulate matter ($\text{PM}_{10}$) in cities, but at the same time raises the pH of rain in acidified rural areas. Justify the mineralogical composition of the dust responsible for this buffering effect.
2. b) In Scandinavian lakes on granitic bedrock, acid rain caused the disappearance of entire fish communities, whereas in Iberian lakes on calcareous bedrock, damage was negligible under equivalent acid loads. Provide a chemical justification for this difference in vulnerability and deduce the mechanism of sulfuric acid formation from $\text{SO}_2$ during its atmospheric transport.
3. c) Design a method that allows the environmental authorities of an autonomous community to demonstrate scientifically to the European Commission whether an exceedance of the daily $\text{PM}_{10}$ limit ($50\ \mu\text{g/m}^3$) is exclusively due to a Saharan haze event or to the contribution of local traffic and industry.

A coastal municipality approves the construction of a continuous row of 22-story residential towers just a few meters from the beach, replacing a previous strip of low-density single-family homes with trees.

1. a) Justify thermodynamically how the daytime sea breeze develops and predict how the architectural barrier will alter the penetration of the airflow and its velocity toward inland neighborhoods located $2\ \text{km}$ from the coast, taking into account aerodynamic surface roughness.
2. b) During a summer heatwave, reason how this physical obstacle and the replacement of vegetation with asphalt and concrete intensify the nocturnal urban heat island effect and hinder air renewal under land breeze conditions (nighttime land breeze).
3. c) Design three binding urban planning criteria (regarding the orientation of main roadways relative to the coastline, building height staggering, and ground albedo/permeability) that should be incorporated into the project to ensure effective sea ventilation corridors and optimize thermal comfort in the interior of the city.