AP Environmental Science

An ecosystem 生态系统 is all the living things (biotic) and non-living things (abiotic) in an area, interacting together. Organisms depend on each other and on their physical environment, and interactions like predation 捕食, competition 竞争, and symbiosis 共生 (mutualism, commensalism, parasitism) shape the community.

A biome 生物群系 is a large region defined by its climate and characteristic life. Terrestrial biomes (deserts, grasslands, tropical rainforest, temperate forest, taiga, tundra) are determined mainly by temperature and precipitation 降水. Each has plants and animals adapted to those conditions.

Aquatic biomes cover more of Earth than land. Freshwater (streams, lakes, wetlands) and marine (open ocean, coral reefs, estuaries) systems differ in salinity 盐度, sunlight, and nutrients. Estuaries 河口 (where rivers meet the sea) and coral reefs are especially productive and biodiverse.

The carbon cycle 碳循环 moves carbon between the atmosphere, organisms, oceans, and rocks. Photosynthesis removes $\text{CO}_2$; respiration, decomposition, and burning fossil fuels 化石燃料 return it. Burning fossil fuels adds carbon far faster than natural processes remove it.

The carbon cycle moves carbon among the atmosphere, living things, and fossil fuels

The nitrogen cycle 氮循环 makes nitrogen usable for life. Nitrogen fixation 固氮 (by bacteria) converts atmospheric $\text{N}_2$ to ammonia; nitrification and assimilation pass it through organisms; denitrification returns $\text{N}_2$ to the air. Fertilizer adds reactive nitrogen, which can pollute water.

The nitrogen cycle: N$_2$ is fixed into soil nitrates, passed through food, and returned to the air by denitrification

The phosphorus cycle 磷循环 has no atmospheric (gas) stage – phosphorus moves through rock, soil, water, and organisms. It is slow and often the limiting nutrient 限制性营养 for growth, so added phosphorus (fertilizer, detergents) can trigger algal blooms.

The phosphorus cycle: rock weathers to soil phosphate and slowly sediments back, with no gas phase

The water cycle 水循环 moves water by evaporation 蒸发, transpiration 蒸腾 (from plants), condensation, precipitation, and runoff. It distributes fresh water and shapes climate; human use and land changes can alter its flow.

The water cycle: evaporation and transpiration lift water to the air; precipitation and runoff return it

Primary productivity 初级生产力 is the rate at which producers capture energy (usually by photosynthesis). Gross primary productivity (GPP) is the total captured; net primary productivity (NPP) is what remains after the producers' own respiration – the energy available to the rest of the ecosystem. Warm, wet, sunlit systems (rainforests, reefs) are most productive.

Worked example. If producers in a grassland capture $20{,}000\ \text{kcal/m}^2/\text{yr}$ of energy (GPP) and burn $8{,}000\ \text{kcal/m}^2/\text{yr}$ in their own respiration, then $\text{NPP}=\text{GPP}-R=20{,}000-8{,}000=12{,}000\ \text{kcal/m}^2/\text{yr}$. Only that NPP – not the full GPP – is available to the consumers above.

Organisms occupy trophic levels 营养级: producers 生产者 (make their own food), then primary, secondary, and tertiary consumers 消费者, with decomposers 分解者 recycling nutrients at every level. Each level depends on the energy captured below it.

Energy flows one way through an ecosystem and is lost as heat at each transfer. The 10% rule: only about 10% of the energy at one trophic level passes to the next; the other 90% powers life processes and escapes as heat. This is why food chains are short and top predators are few.

Worked example. Continuing from $12{,}000\ \text{kcal/m}^2/\text{yr}$ of NPP at the producer level, the primary consumers receive about $10\%=1{,}200\ \text{kcal}$, secondary consumers $\approx120\ \text{kcal}$, and tertiary consumers only $\approx12\ \text{kcal}$. After three transfers the energy has shrunk a thousand-fold – the arithmetic reason a fourth or fifth trophic level rarely has enough to support it.

An energy pyramid: only about 10% of energy passes to the next trophic level

A food chain 食物链 is a single line of who-eats-whom; a food web 食物网 links many chains into a realistic picture of feeding relationships. Because species are interconnected, removing one (especially a keystone species 关键种) can disrupt the whole web.

A food web links many food chains; arrows point the way energy flows

• Remember energy flows and is lost (the 10% rule) while matter cycles (carbon, nitrogen, phosphorus, water).
• Apply the 10% rule down a food chain and know NPP = GPP − respiration (only NPP is available to consumers).
• Learn each biogeochemical cycle's stores and how humans disturb it (burning fossil fuels adds CO₂; fertiliser adds nitrogen/phosphorus).
• Producers are most abundant because so little energy reaches the top.
• Use correct units and show your arithmetic on the free-response math questions (no calculator — keep numbers round).

Biodiversity 生物多样性 is the variety of life, measured at three levels:

• Genetic diversity – variety of genes within a species. More genetic variety means a population can better respond to environmental stressors 环境压力; a population bottleneck 种群瓶颈 (a sharp drop in numbers) throws that variety away and leaves the survivors vulnerable.
• Species diversity – the number of species (species richness 物种丰富度) and how evenly individuals are spread among them.
• Habitat diversity – the variety of habitats in a region.

More species-rich ecosystems are more resilient 有韧性的: they recover from disruption more readily, because varied species can fill roles when conditions change. Habitat loss removes species in a predictable order – specialist 特化 species (narrow needs) go first, then the hardier generalist 广适性 species, and species that need large territories decline as their range shrinks.

Biodiversity has three levels: genetic, species, and habitat

Ecosystem services 生态系统服务 are the free benefits nature gives people, in four categories:

• Provisioning – products: food, fresh water, timber, fibre.
• Regulating – processes that keep conditions stable: climate regulation, water filtration, pollination, flood control.
• Cultural – non-material value: recreation, beauty, spiritual and educational value.
• Supporting – the services that make the others possible: nutrient cycling, soil formation, photosynthesis.

Anthropogenic 人为的 (human-caused) activities can disrupt these services, with real economic and ecological costs – for example, losing pollinators forces farmers to pay for pollination that bees once did for free.

Island biogeography 岛屿生物地理学 studies how many species an island (or any isolated habitat patch) holds. The number settles at a balance between two rates:

• Immigration of new species – higher for islands closer to the mainland.
• Extinction of resident species – lower on larger islands.

So big, near islands hold the most species; small, remote ones the fewest. Isolation also drives evolution: island species often become specialists because resources are limited, and many are endemic 特有 – found nowhere else. That makes them fragile. When an invasive species 入侵物种 (usually a tough generalist) arrives, it can outcompete the specialists, which have nowhere else to go.

Larger and nearer islands hold more species, balancing immigration against extinction

Every species has a range of tolerance 耐受范围 – the span of conditions (temperature, salinity, pH, sunlight) it can survive. Near the middle is an optimal range 最适范围 where individuals thrive; toward the edges are zones of stress 胁迫区 where they survive but struggle to grow or reproduce; beyond the limits they die. Ecological tolerance 生态耐受性 applies both to a single individual and to a whole species, and it decides where an organism can live and how it copes with change.

Within its optimal range a species thrives; toward the limits it is stressed, then cannot survive

Natural events disrupt ecosystems across every timescale, and a single natural event can rival or exceed a human-made one. Earth's processes come in three timing patterns:

• Periodic 周期性 – regular cycles (seasons, tides).
• Episodic 偶发性 – occasional, irregular events (fires, floods, volcanic eruptions).
• Random 随机 – no pattern (a meteor strike).

Over geological time, Earth's climate has shifted for many reasons, and sea level has risen and fallen with the amount of glacial ice – each change reshaping large swaths of habitat. Wildlife responds by migration 迁徙, moving short or long distances to follow conditions.

An adaptation 适应 is an inherited trait that improves survival and reproduction in an environment. Adaptations arise through natural selection 自然选择 – incremental genetic change accumulating over generations, not within a single lifetime. When the environment changes, individuals must alter their behaviour, move, or die; if change comes faster than a population can adapt, it declines. A periodic disturbance such as fire is often part of a healthy cycle, and many species are adapted to it (some pine cones open only in a fire's heat).

Ecological succession 生态演替 is the gradual, orderly change in a community over time:

• Primary succession 初级演替 starts on bare rock with no soil – after a glacier retreats or lava cools. Pioneer species 先锋物种 such as lichens 地衣 arrive first and slowly build soil. It is slow.
• Secondary succession 次级演替 follows a disturbance that leaves the soil intact – after a fire or abandoned farming – so it is much faster.

Succession tends toward a relatively stable climax community 顶极群落. Two special roles shape a community out of proportion to their numbers: a keystone species 关键种, whose activities hold the community structure together (remove it and the community collapses – sea otters keeping urchins in check), and an indicator species 指示物种, whose presence or health signals the condition of the whole ecosystem (lichens vanish where the air is polluted).

Primary succession builds from bare rock; secondary succession regrows from surviving soil

• Describe biodiversity at three levels: genetic, species, and habitat, and link higher diversity to greater resilience.
• Specialist species (narrow needs) are more vulnerable than generalists when a habitat changes.
• Distinguish primary succession (bare rock, no soil, slow) from secondary (soil intact, faster).
• Explain a keystone species (outsized effect) and an indicator species (signals ecosystem health).
• Name the four ecosystem services (provisioning, regulating, cultural, supporting) with examples.

A generalist 广适性物种 can live in many habitats and eat many foods (raccoon, cockroach) – flexible, so it copes well with change. A specialist 狭适性物种 needs specific conditions or foods (panda, koala) – efficient in a stable habitat but very vulnerable if that habitat changes.

Two reproductive strategies:

• $r$-selected species produce many offspring with little care, mature fast, and have short lives (insects, weeds). They colonize quickly and boom-and-bust.
• $K$-selected species produce few offspring with much care, mature slowly, and live long (elephants, humans). They do well near carrying capacity in stable environments but recover slowly from losses.

A survivorship curve 存活曲线 plots how many individuals survive at each age (on a log scale). Type I (humans): most survive to old age, then die – a convex curve. Type II (many birds): a constant death rate at all ages – a straight line. Type III ($r$-selected: fish, insects): most die young, a few survive – a concave curve.

Type I, II, and III survivorship curves on a log scale

The carrying capacity 环境容纳量 ($K$) is the maximum population an environment can support long-term. A population may overshoot $K$ when resources are temporarily plentiful, then crash (dieback) as resources run out. Populations tend to fluctuate around $K$.

Population growth levels off at the carrying capacity of the environment

With abundant resources a population grows exponentially 指数增长 ($J$-curve). As resources become limited, growth slows to logistic 逻辑斯蒂增长 ($S$-curve), leveling at $K$. Limiting factors 限制因素 (food, water, space, disease) set the ceiling.

An age-structure diagram 年龄结构图 shows the proportion of a population in each age group. A wide base (many young) predicts rapid growth; even bars predict a stable population; a narrow base predicts decline. They forecast a country's future population.

Population pyramids of a developing and a developed country

The total fertility rate 总生育率 (TFR) is the average number of children per woman. A replacement level of about 2.1 keeps a population steady; above it grows, below it shrinks. TFR falls with education, access to family planning, and lower infant mortality.

Human population growth depends on birth rate, death rate, and migration. Rapid growth strains resources and increases the ecological footprint 生态足迹. Factors lowering birth rates include education (especially of women), urbanization, and economic development.

Worked example. A country has a birth rate of $30$ per $1000$ and a death rate of $10$ per $1000$. The natural growth rate is $\dfrac{30-10}{10}=2.0\%$ per year (dividing the per-thousand difference by $10$ converts it to a percent). By the rule of 70, the population doubles in about $\dfrac{70}{2.0}=35$ years. If development cut the growth rate to $1.0\%$, the doubling time would stretch to $\dfrac{70}{1.0}=70$ years.

The demographic transition 人口转型 describes how a country's growth changes as it develops, in stages: (1) high birth and death rates (slow growth); (2) death rate falls (rapid growth); (3) birth rate falls (slowing growth); (4) both low (stable). Developed nations are in later stages; many developing nations are in the rapid-growth stages.

The four stages of the demographic transition

The population grows fastest in stages 2 and 3 – the gap between a still-high birth rate and an already-fallen death rate. That lag is why a country's population keeps climbing long after its death rate drops.

• Use the rule of 70: doubling time ≈ 70 ÷ growth-rate(%); a growth rate is (births − deaths) per 1000 ÷ 10.
• Read age-structure diagrams: a wide base predicts rapid growth, even bars a stable population.
• Contrast r-selected (many offspring, little care) and K-selected (few, much care) strategies.
• Know the demographic transition stages and what lowers birth rates (education, family planning, development).
• A falling growth rate still means growth — the population only shrinks when deaths exceed births.

Earth's crust is broken into plates 板块 that slowly move on the mantle – plate tectonics 板块构造. At divergent boundaries plates spread apart (new crust); at convergent they collide (mountains, volcanoes, earthquakes); at transform they slide past (earthquakes). Boundaries create hazards but also volcanic soils and mineral resources.

Soil 土壤 forms slowly as rock weathers 风化 and organic matter builds up. Erosion 侵蚀 is the removal of soil by wind and water, sped up by removing vegetation (farming, deforestation, overgrazing). Because soil forms so slowly, erosion faster than formation depletes a vital resource.

Soil is a mix of sand, silt, and clay (its texture 质地), plus organic matter, water, and air, layered in horizons 土层. Texture controls porosity 孔隙度 and permeability 渗透性 – how well soil holds water and nutrients. Loam (a balanced mix) is best for plants.

The atmosphere 大气层 is layered: the troposphere 对流层 (weather, where we live), the stratosphere 平流层 (holding the ozone layer), and higher layers. It is mostly nitrogen and oxygen, with trace gases (including greenhouse gases) that regulate temperature.

Clean dry air is about 78% nitrogen, 21% oxygen, and 1% other gases

Uneven solar heating drives global wind patterns 全球风带. Warm air rises at the equator and sinks at about 30°, creating convection cells 对流环流 (Hadley, Ferrel, polar) and prevailing winds (trade winds, westerlies). The spinning Earth deflects winds – the Coriolis effect 科里奥利效应 – shaping weather and climate.

Three circulation cells per hemisphere set the prevailing surface winds

A watershed 流域 is all the land that drains to a common body of water. Everything that happens on the land – farming, paving, pollution – affects the water it drains into, so watersheds are key units for managing water quality.

Seasons come from Earth's tilted axis (about 23.5°), not its distance from the Sun. The hemisphere tilted toward the Sun gets more direct sunlight and longer days (summer). The tilt also makes the tropics warm year-round and the poles cold.

The tilt of the Earth's axis causes the seasons

Geography shapes climate: latitude (sunlight angle), elevation (cooler with height), proximity to oceans (moderating temperature), and mountains creating a rain shadow 雨影 (wet windward side, dry leeward side). These factors decide which biome forms where.

El Niño 厄尔尼诺 and La Niña 拉尼娜 are periodic shifts in Pacific Ocean temperatures and winds. El Niño (warm eastern Pacific) and La Niña (cool eastern Pacific) alter rainfall, storms, and fisheries worldwide – for example, floods in some regions and droughts in others.

• Seasons come from the Earth's tilt, not its distance from the Sun.
• Soil forms very slowly, so erosion faster than formation permanently depletes it; know soil texture (sand/silt/clay) and horizons.
• Explain global wind patterns from uneven heating + the Coriolis effect, and a rain shadow (wet windward, dry leeward).
• Name the atmospheric layers (troposphere = weather, stratosphere = ozone) and air composition (~78% N₂, 21% O₂).
• El Niño / La Niña are Pacific temperature shifts that change rainfall worldwide.

The tragedy of the commons 公地悲剧: when a resource is shared and open to all (a fishery, the atmosphere, a pasture), each user takes as much as they can for private gain, and the shared resource is overused and degraded for everyone. Solutions require regulation, privatization, or cooperative management.

Clearcutting 皆伐 removes all trees from an area at once. It is cheap and efficient but causes erosion 侵蚀, loss of habitat and biodiversity, flooding, and higher soil temperatures. Recovery is slow, and nearby streams suffer from sediment.

Deforestation lowers biodiversity and causes erosion, flooding, and higher CO2

The Green Revolution 绿色革命 boosted crop yields with high-yield seeds, synthetic fertilizers 化肥, pesticides 农药, irrigation, and mechanization. It fed billions but brought costs: soil degradation, water pollution, high energy and water use, and loss of crop diversity (monoculture 单一栽培).

NPK fertilisers supply the three elements plants need most

Practices such as tilling, monoculture, and heavy fertilizer/pesticide use cause erosion, soil salinization 土壤盐碱化, nutrient runoff (causing eutrophication 富营养化), and loss of biodiversity. Sustainable methods reduce these harms.

Irrigation 灌溉 supplies water to crops. Drip irrigation is the most efficient (least evaporation); flood and spray methods waste more water and can cause waterlogging and salinization as evaporation leaves salts behind. Over-irrigation depletes aquifers.

Irrigation methods compared: drip wastes the least water, flooding the most

Pesticides kill pests and raise yields, but cause problems: they harm non-target species, pollute water, and drive pesticide resistance 抗药性 (survivors breed, so stronger doses are needed – the "pesticide treadmill").

Producing meat, especially in concentrated animal feeding operations (CAFOs), uses large amounts of land, water, feed, and energy, and generates waste and methane 甲烷 (a greenhouse gas). Meat is far less energy-efficient than plant food because of the 10% rule – higher trophic levels waste more energy.

Overfishing 过度捕捞 removes fish faster than they reproduce, collapsing populations (like cod). Bycatch (unwanted catch) and destructive methods (bottom trawling) damage ecosystems. It is a classic tragedy of the commons in the open ocean.

Mining 采矿 extracts minerals and fuels but disturbs land, especially surface (strip) mining and mountaintop removal. Impacts include habitat destruction, acid mine drainage 酸性矿山废水, and toxic tailings polluting water.

Urbanization 城市化 replaces natural land with impervious surfaces 不透水面 (roads, buildings), increasing runoff and flooding, creating urban heat islands 热岛, and generating pollution and waste. Urban sprawl consumes farmland and habitat.

An ecological footprint 生态足迹 measures the land and water a person or population needs to supply resources and absorb wastes. Wealthy, high-consumption nations have much larger footprints. If everyone's footprint exceeds Earth's capacity, resources are being used unsustainably.

Worked example. Earth provides roughly $1.6$ global hectares (gha) of biocapacity per person. If the average person's footprint is $2.7\ \text{gha}$, humanity is demanding about $\tfrac{2.7}{1.6}\approx1.7$ Earths – living beyond what the planet can renew. Worse, if everyone consumed like a high-income nation at $8\ \text{gha}$ per person, it would take $\tfrac{8}{1.6}=5$ Earths – exactly why footprint-per-person is the key sustainability yardstick.

Sustainability 可持续性 means meeting present needs without harming future generations' ability to meet theirs. It balances environmental health, economic viability, and social equity, using resources no faster than they can be replaced.

Reduce runoff with permeable pavement 透水路面, rain gardens and green roofs 绿色屋顶, retention ponds, and preserved vegetation. These let water soak in, filtering pollutants and recharging groundwater instead of flooding streams.

Integrated pest management 综合虫害管理 (IPM) combines methods – biological controls (natural predators), crop rotation, limited targeted pesticides, and monitoring – to control pests with less chemical use, slowing resistance and protecting non-target species.

Sustainable farming protects soil and water: crop rotation 轮作, cover crops, contour plowing 等高耕作, terracing 梯田, reduced tillage, and agroforestry. These cut erosion, maintain fertility, and reduce chemical inputs.

Aquaculture 水产养殖 (fish farming) eases pressure on wild stocks and is efficient, but can pollute water with waste and antibiotics, spread disease to wild fish, and destroy habitat (like mangroves for shrimp farms).

Sustainable forestry keeps forests productive: selective cutting 择伐 instead of clearcutting, replanting, leaving buffer strips along streams, and long rotation times. It maintains habitat, prevents erosion, and lets forests keep providing ecosystem services.

• Explain the tragedy of the commons — shared, unowned resources get overused — and how rules/ownership prevent it.
• Weigh the trade-offs of the green revolution, irrigation (salinisation, aquifer depletion), and mining/urbanisation.
• Compute an ecological footprint in "number of Earths" (footprint ÷ biocapacity per person); it is measured per person.
• List the harms of deforestation (erosion, flooding, lost habitat, more CO₂).
• Define sustainability (meeting needs without harming future generations) and give sustainable methods (IPM, crop rotation, quotas).

A renewable resource 可再生资源 replenishes on a human timescale (sun, wind, water, biomass); a nonrenewable resource 不可再生资源 exists in fixed amounts that take millions of years to form (fossil fuels, nuclear fuel). Nonrenewables will eventually run out and often pollute more.

Global energy use is rising, especially in developing nations. Most energy still comes from fossil fuels 化石燃料. Wealthy nations consume the most per person; access to energy shapes economic development.

Different fuels suit different needs: coal and natural gas for electricity, oil for transportation, and biomass for heating and cooking in many regions. Each has trade-offs in cost, availability, and pollution.

Energy resources are unevenly distributed – oil is concentrated in some regions, coal in others, and renewables depend on local sun, wind, or rivers. This uneven distribution drives trade, economics, and geopolitics.

Fossil fuels (coal, oil, natural gas) formed from ancient organisms. They are energy-dense and reliable but nonrenewable and the main source of $\text{CO}_2$ and air pollution. Coal is the dirtiest; natural gas burns cleaner but leaks methane 甲烷.

Nuclear power 核能 splits uranium (fission 裂变) to boil water and drive turbines. It produces no $\text{CO}_2$ and lots of energy from little fuel, but risks include radioactive waste 核废料 (long-lived), the danger of meltdowns, and high cost.

Worked example. Radioactive waste decays by its half-life – the time for half of it to decay. Suppose an isotope has a half-life of $30$ years and a reactor leaves $100\ \text{g}$ of it. After $30$ years $50\ \text{g}$ remains; after $60$ years $25\ \text{g}$; after $90$ years (three half-lives) $100\times\left(\tfrac12\right)^3=12.5\ \text{g}$. Because the drop is halving, not linear, the waste stays hazardous for many half-lives – the core reason it must be stored safely for centuries.

Nuclear fission of a uranium-235 nucleus releases energy

Biomass 生物质 (wood, crops, waste, biofuels like ethanol) is renewable and can be carbon-neutral if replanted, but burning it causes air pollution, and growing fuel crops competes with food and habitat.

Solar 太阳能 converts sunlight to electricity (photovoltaic panels) or heat. It is renewable and clean during use, but intermittent (no sun at night), needs space, and has manufacturing impacts.

Hydroelectric 水电 power uses flowing water (dams) to spin turbines – renewable and low-emission, but dams flood habitat, block fish migration, trap sediment, and displace people.

Geothermal 地热能 taps Earth's internal heat for electricity and heating. It is renewable and reliable, but only practical where hot rock is near the surface (volcanic regions) and can release underground gases.

A hydrogen fuel cell 氢燃料电池 combines hydrogen and oxygen to make electricity, with water as the only emission at use. But producing hydrogen usually requires energy (often from fossil fuels), and storage is difficult.

A hydrogen-oxygen fuel cell makes electricity, with water as the only product

Wind 风能 turbines convert moving air to electricity – renewable, clean, and low-operating-cost, but intermittent, land- or sea-intensive, and a hazard to birds and bats. Best where winds are strong and steady.

Energy conservation 节能 reduces demand through efficiency (LED lighting, insulation, efficient appliances, public transport) and behavior. Saving energy is often the cheapest and cleanest option – the energy you do not use needs no fuel and makes no pollution.

Worked example. Replacing a $60\ \text{W}$ incandescent bulb with a $10\ \text{W}$ LED that gives the same light saves $50\ \text{W}$. Running it $5$ hours a day saves $50\ \text{W}\times5\ \text{h}=250\ \text{Wh}=0.25\ \text{kWh}$ per day, or about $0.25\times365\approx91\ \text{kWh}$ per year. Multiply that by every bulb in a city and conservation rivals a new power plant – at far lower cost.

• Separate renewable (sun, wind, water) from non-renewable (fossil fuels, nuclear) and weigh each source's trade-offs.
• Fossil fuels are energy-dense but emit CO₂; nuclear emits no CO₂ but leaves long-lived waste.
• Do half-life math: after $n$ half-lives a fraction $(\tfrac12)^n$ remains.
• Note that solar and wind are intermittent and need storage or backup.
• Conservation (efficiency) is often the cheapest, cleanest option — the energy not used needs no fuel.

Air pollution 空气污染 is harmful substances in the atmosphere. Primary pollutants 一次污染物 are emitted directly (carbon monoxide, nitrogen oxides, sulfur dioxide, particulates); secondary pollutants 二次污染物 form in the air from reactions (like ozone in smog). Most come from burning fossil fuels in vehicles, power plants, and industry.

Photochemical smog 光化学烟雾 forms when sunlight drives reactions among nitrogen oxides and volatile organic compounds from car exhaust, producing ground-level ozone 臭氧. It is worst in sunny, car-heavy cities and harms lungs. (Ground-level ozone is a pollutant, unlike the protective ozone layer high up.)

A thermal inversion 逆温 traps pollution near the ground. Normally warm air rises and carries pollutants away, but in an inversion a layer of warm air sits above cooler air, capping it. Pollutants accumulate below – causing dangerous smog episodes, especially in valleys.

Normally warm air rises and disperses pollution; an inversion caps it near the ground

Rising atmospheric $\text{CO}_2$ from fossil fuels enhances the greenhouse effect and warms the climate. Particulate matter 颗粒物 (tiny solid/liquid particles, PM2.5 and PM10) penetrates deep into lungs, causing respiratory and heart disease, and reduces visibility.

Indoor air can be more polluted than outdoor. Common indoor pollutants include radon 氡 (radioactive gas from the ground, a lung-cancer risk), carbon monoxide, asbestos 石棉, tobacco smoke, mold, and VOCs from paints and furnishings. Ventilation and source control reduce exposure.

Air pollution is cut by technology and policy: catalytic converters 催化转化器 on cars, scrubbers 洗涤器 and electrostatic precipitators 静电除尘器 on smokestacks, cleaner fuels, and laws like the Clean Air Act setting emission limits. Reducing fossil-fuel use addresses the root cause.

A catalytic converter turns harmful NO and CO into harmless N2 and CO2

Acid rain 酸雨 forms when sulfur dioxide and nitrogen oxides react with water in the air to make sulfuric and nitric acids, which fall far downwind. It acidifies lakes and soils (harming fish and trees), leaches nutrients, and corrodes buildings. Reducing $\text{SO}_2$ and $\text{NO}_x$ emissions is the fix.

Nitrogen and sulfur oxides form nitric and sulfuric acid in rain

Noise pollution 噪声污染 is unwanted or harmful sound in the environment. Major sources are road traffic, aircraft, trains, industry, and construction. In people, long or loud exposure causes hearing loss 听力损失, stress 压力, sleep loss, and higher blood pressure. It also disturbs wildlife 野生动物: it masks the sounds animals use to communicate, navigate, and find mates, and underwater noise from ships is especially harmful to whales and dolphins. It is reduced by sound barriers, quieter engines and mufflers, and land-use planning such as buffer zones around airports.

• Distinguish primary pollutants (emitted directly: CO, NOₓ, SO₂, particulates) from secondary (form in the air: ground-level ozone).
• Ground-level ozone is a pollutant, but the ozone layer high up is protective — do not confuse them.
• Explain how a thermal inversion traps pollution near the ground.
• Acid rain (from SO₂ and NOₓ) often falls far downwind, making it an international problem.
• Link control methods to pollutants (catalytic converters, scrubbers, cleaner fuels, emission laws).

Pollution sources are point or nonpoint. A point source 点源 comes from a single, identifiable place (a factory pipe, a sewage outfall) – easy to locate and regulate. A nonpoint source 非点源 is spread out (farm runoff, urban street runoff, car exhaust) – much harder to control because it comes from everywhere.

Human activities – pollution, habitat destruction, overharvesting, introducing species – degrade ecosystems and reduce biodiversity. Because species are interconnected, harming one part can ripple through the whole system.

Endocrine disruptors 内分泌干扰物 are chemicals (some pesticides, plasticizers like BPA) that mimic or block hormones, disrupting growth, reproduction, and development in wildlife and humans even at very low doses.

Wetlands 湿地 and mangroves 红树林 filter pollutants, store floodwater, and nurse young fish, but they are drained and cleared for farms, shrimp ponds, and development. Losing them removes valuable ecosystem services and coastal protection.

Eutrophication 富营养化 happens when excess nutrients (nitrogen, phosphorus from fertilizer and sewage) trigger algal blooms 藻华. When the algae die, decomposers use up the oxygen, creating hypoxic 缺氧 "dead zones" that suffocate fish.

Extra fertiliser makes algae bloom, then the water loses its oxygen

Thermal pollution 热污染 is heat added to water, usually from power-plant cooling. Warm water holds less dissolved oxygen and stresses aquatic life adapted to cooler temperatures.

Persistent organic pollutants 持久性有机污染物 (POPs, like DDT and PCBs) resist breakdown, so they last for decades, travel far, and are fat-soluble, so they build up in organisms. This sets up bioaccumulation and biomagnification.