Environmental Chemistry flash cards

1. 1.What is environmental pollution?

   The effect of undesirable changes in our surroundings that have harmful effects on plants, animals and human beings, caused by pollutants.

   Hint: undesirable + harmful change

2. 2.Define a pollutant and give the two broad types.

   A pollutant is a substance present in nature in greater than natural abundance, produced by human activity, that has a detrimental effect. Types: biodegradable (e.g. sewage) and non-biodegradable (e.g. DDT, plastics, heavy metals).

   Hint: can nature break it down?

3. 3.Distinguish a contaminant from a pollutant.

   A contaminant is a substance that does not occur in nature but is introduced by human activity; once it exerts a harmful effect it is called a pollutant.

   Hint: contaminant → harm → pollutant

4. 4.What are the three major segments of the atmosphere studied in pollution (by altitude, lowest first)?

   Troposphere ($0$–$10$ km), Stratosphere ($10$–$50$ km, contains ozone layer), then mesosphere/thermosphere above.

   Hint: tropo = weather layer

5. 5.What is the troposphere and why is it called the turbulent/weather region?

   The lowest layer ($0$–$10$ km) where humans live; it is turbulent, dusty, contains air and water vapour, and is where clouds and weather form.

   Hint: 'tropos' = to turn/mix

6. 6.What key gas defines the stratosphere and what is its role?

   Ozone ($O_3$). The ozone layer absorbs harmful UV radiation, protecting life on Earth.

   Hint: UV shield

7. 7.Define tropospheric pollution.

   Pollution occurring due to the presence of undesirable solid or gaseous particles in the air of the lowest atmospheric layer.

   Hint: gaseous + particulate near ground

8. 8.Name the two categories of tropospheric air pollutants.

   Gaseous pollutants (oxides of S, N, C; hydrocarbons; ozone) and particulate pollutants (dust, mist, fumes, smoke, smog).

   Hint: gas vs particle

9. 9.Which oxides of sulphur are common air pollutants and their main source?

   $SO_2$ and $SO_3$; produced mainly by combustion of fossil fuels (coal, petroleum) containing sulphur.

   Hint: burning coal

10. 10.State the harmful effects of $SO_2$ on humans and plants.

    Even low $SO_2$ causes irritation to the respiratory tract, throat and eye problems, breathing difficulty; in plants it causes chlorosis (loss of chlorophyll) and stiffness of flower buds.

    Hint: respiratory + chlorosis

11. 11.How is $SO_2$ oxidised to $SO_3$ in the atmosphere, and its consequence?

    $2 SO_2 + O_2 \rightarrow 2 SO_3$ (catalysed by particulate matter); $SO_3 + H_2O \rightarrow H_2SO_4$, contributing to acid rain.

    Hint: SO2 → SO3 → H2SO4

12. 12.Which oxides of nitrogen are pollutants, and how does NO form naturally at high altitude?

    $NO$ and $NO_2$ (together $NO_x$). At high altitude/high temperature (lightning, engines): $N_2 + O_2 \rightarrow 2 NO$.

    Hint: needs high T

13. 13.How does $NO$ convert to $NO_2$ and why is $NO_2$ especially harmful?

    $2 NO + O_2 \rightarrow 2 NO_2$. $NO_2$ is a strong oxidising agent, irritates the lungs, damages leaves, retards photosynthesis, and is a key player in photochemical smog and acid rain.

    Hint: brown gas, oxidiser

14. 14.What is the main anthropogenic source of $NO_x$ pollution?

    High-temperature combustion in automobile engines and industrial furnaces, where atmospheric $N_2$ and $O_2$ combine.

    Hint: vehicle exhaust

15. 15.Why is carbon monoxide ($CO$) so dangerous to humans?

    $CO$ binds to haemoglobin ~$300$ times more strongly than $O_2$, forming carboxyhaemoglobin, blocking oxygen transport; causes headache, hypoxia and can be fatal.

    Hint: binds Hb, blocks O2

16. 16.Give the main sources of carbon monoxide.

    Incomplete combustion of carbon fuels (automobile exhaust, burning of coal/wood/charcoal in limited air) and cigarette smoke.

    Hint: incomplete burning

17. 17.Why is $CO_2$ considered a pollutant despite being natural?

    In excess (from fossil-fuel burning, deforestation, cement) it enhances the greenhouse effect, causing global warming.

    Hint: greenhouse gas

18. 18.What are the three main sinks that remove atmospheric $CO_2$?

    Green plants (photosynthesis) and the oceans (dissolution), with limited soil/rock weathering.

    Hint: photosynthesis + oceans

19. 19.How do hydrocarbons enter the atmosphere and what are their effects?

    From incomplete combustion of fuel and unburnt petrol/diesel vapours; they are carcinogenic, cause premature ageing of plants, and help form photochemical smog.

    Hint: unburnt fuel, cancer-causing

20. 20.Define particulate pollutants and give the two subtypes.

    Minute solid or liquid particles suspended in air. Subtypes: viable (living — bacteria, fungi, algae) and non-viable (non-living — smoke, dust, mist, fumes).

    Hint: living vs non-living particles

21. 21.Differentiate smoke, dust, mist and fumes (non-viable particulates).

    Smoke = solid/liquid particles from combustion (e.g. cigarette, oil smoke); dust = solid particles from grinding/crushing; mist = liquid droplets from sprays/condensation; fumes = condensed vapours of metals/organics.

    Hint: origin distinguishes them

22. 22.What health effect do fine particulates (<$5$ µm) have?

    Particles smaller than $5$ µm can lodge deep in the lungs, causing respiratory diseases like asthma, bronchitis and lung damage.

    Hint: deep-lung penetration

23. 23.What is smog and where does the word come from?

    A combination of smoke + fog; a common form of air pollution seen especially in industrial cities.

    Hint: smoke + fog

24. 24.Describe classical (London/reducing) smog.

    Occurs in cool humid climate; a mixture of smoke, fog and $SO_2$; chemically reducing in nature (so also called reducing smog).

    Hint: cold + SO2 + reducing

25. 25.Describe photochemical (Los Angeles) smog.

    Occurs in warm, dry, sunny climate; formed from the action of sunlight on $NO_x$ and hydrocarbons from vehicles; chemically oxidising in nature.

    Hint: sunlight + NOx + oxidising

26. 26.List the main constituents of photochemical smog.

    Ozone ($O_3$), nitric oxide, acrolein, formaldehyde and PAN (peroxyacetyl nitrate) — plus other aldehydes.

    Hint: O3 + PAN + aldehydes

27. 27.Outline how photochemical smog forms (key steps).

    $NO_2 \xrightarrow{h\nu} NO + O$; $O + O_2 \rightarrow O_3$; $NO + O_3 \rightarrow NO_2 + O_2$. $O_3$ and $NO$ then react with unburnt hydrocarbons to give aldehydes, PAN and acrolein.

    Hint: NO2 photolysis starts it

28. 28.Why is ozone at ground level a pollutant while stratospheric ozone is beneficial?

    Tropospheric (ground-level) $O_3$ is a toxic oxidant in smog harming lungs and plants; stratospheric $O_3$ shields Earth from UV. Same molecule — 'good up high, bad nearby'.

    Hint: location decides

29. 29.State the harmful effects of photochemical smog.

    Irritation to eyes, nose and throat; headache; chest pain; dryness of throat; cough; damage to plant life, rubber, and building materials (metals corrode).

    Hint: eye irritation + material damage

30. 30.How can photochemical smog be controlled?

    Use catalytic converters in vehicles to prevent release of $NO_x$ and hydrocarbons; plant certain trees (e.g. Pinus, Juniperus) that metabolise $NO_2$.

    Hint: catalytic converter

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