Notes
Air pollutants
- The atmosphere is mostly nitrogen and oxygen. Weather occurs in the troposphere; the ozone layer is in the stratosphere.
- Primary pollutants are emitted directly; secondary pollutants form in the air. EPA criteria pollutants: CO, lead, $NO_2$, ground-level $O_3$, particulates, and $SO_2$. The Clean Air Act (1970) regulates them.
- Photochemical smog forms from $NO_x$ and VOCs in sunlight. Temperature inversions trap pollution.
Acid rain and ozone
- Acid rain (pH below 5.6) forms from $SO_2$ and $NO_x$; each pH unit is a factor of 10. Scrubbers and cleaner energy reduce it.
- The ozone layer blocks UV-B. CFCs destroy ozone; the Montreal Protocol (1987) phased them out.
Greenhouse effect and climate change
- Greenhouse gases ($CO_2$, $CH_4$, $N_2O$, water vapor) absorb infrared heat. The natural effect warms Earth by about 33 $^\circ$C; human emissions enhance it.
- Evidence: rising temperatures, melting ice, sea level rise, ocean acidification, ice core records, and rising $CO_2$ (about 280 ppm to over 420 ppm).
- Mitigation reduces emissions; adaptation adjusts to impacts. People debate which policies are best.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Soot is emitted directly. The others form through reactions in the air.
Two pH units apart means $10 \times 10 = 100$.
Burning fossil fuels raises atmospheric $CO_2$, the largest driver of added warming.
Ozone-depleting chemicals have declined because of the treaty.
Traffic emissions plus sun and trapped air produce ozone.
Water expands as it warms, and land ice adds new water to the oceans.
Free response
Write your answer first, then open the scoring guide.
Free-response question
Air quality monitors in a valley city show high ozone on hot, sunny, calm summer afternoons. The city also reports that nearby lakes have become more acidic.
(a) Identify the type of air pollution that causes the high ozone and name two ingredients needed to form it.
Show the answer and scoring guide
Photochemical smog. It forms from nitrogen oxides and volatile organic compounds reacting in sunlight.
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(b) Explain how a temperature inversion and the valley location could make the problem worse.
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A warm layer of air sits above cooler air near the ground and acts like a lid, so pollutants cannot rise and disperse. Valley walls also limit wind, trapping the polluted air.
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(c) Explain how the burning of coal can lead to the acidification of the lakes, and give one way to reduce it.
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Coal burning releases $SO_2$ (and $NO_x$ from combustion), which form sulfuric and nitric acid in the air. These fall as acid rain and lower lake pH. Installing scrubbers or switching to cleaner energy reduces emissions.
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