Atmospheric Science and PollutionENV 4030 (3 credits)

大气科学与污染

TextbookAtmospheric Pollution

History, Science, and RegulationBy Mark Z. Jacobson

Cambridge 2002

Preface

Atmospheric pollution = air pollution ???

1. Natural air pollution: volcano eruption 火山爆发 , fumaroles 火山喷气孔 , natural fires 自然火灾 , desert

dust 沙尘暴

2. Anthropogenic (manmade 人为 ) air pollution

Air pollution problems on the Earth are as old as the Earth itself

Air is not privately owned; instead, it is common property 共同财产

Manmade pollution

1. Urban smog 城市烟雾 2. Indoor air pollution (indoor air quality, IAQ)3. Acid deposition 酸雨4. Antarctic ozone depletion 南极臭氧层空洞 (global ozone reduction 全球臭氧损耗 )5. Global warming 全球变暖 (green house effect 温室效应 )

Chapter 1Basics and History of Discovery of Atmospheric Chemicals

大气化学物的发现历史

1.6. Summary

In this chapter, atoms, molecules, elements, and compounds were defined and a history of the discovery of elements and compounds of atmospheric importance was given. Only a few elements, including carbon, sulfur, and certain metals, and a few solid compound, including calcite 方解石 , halite 石盐 , and nitre 硝石 , were known in ancient times 古代 . An acceleration of the discovery of elements and compounds, particularly of gases, occurred near the end of the eighteenth century 18 世纪末 1790s.

1.6. Summary (continued)

Several types of chemical reactions 化学反应 occur in the air, including photolysis 光分解 , kinetic 动力学 , thermal decomposition 热分解 , isomerization 异构化 , and combination reactions 化合反应 . The rate of reaction 反应速度 depends on the reactivity 活性 and concentration of molecules. The chemical e-folding lifetime 指数递减时间 of a substance is the time required for its concentration to decrease to 1/e its original value and gives an indication of the reactivity of the substance. Molecules with free electrons自由电子 are called free radicals 自由基 and are highly reactive 高活性 .

e 指数 = 2.718281828…… π 圆周率 = 3.14159265…….

1.1 Basic Definitions

Atmosphere 大气 = Air 空气 ????

Air is a mixture of gases and particles, both of which are made of atoms. In this section, atoms, elements, molecules, compounds, gases, and particles are defined.

A gas consists of individual atoms or molecules that are separated, whereas a particle consists of aggregates 集合体 of atoms or molecules bonded together. Thus, a particle is larger than a single gas atom or molecule. Second, whereas particles contain liquids or solids, gases are in their own phase state.

1.2 History of Discovery of Elements and Compounds of Atmospheric Importance

1.3 Chemical Structure and Reactivity 活性

O3

NO2

A single dot indicates that the atom has a free electron. Compounds with a free electron are called free radicals and are highly reactive. Some nonfree radicals that have a single bond are also reactive because single bonds are readily broken. Compounds with double or triple bonds are not so reactive because they are difficult to break. Noble elements 惰性氣體 has no free electrons and no potential to form bonds with other elements; thus, they are chemically unreactive (inert 惰性 ).

1.4. Chemical reactions and photoprocesses 光反应

Photolysis reactions are unimolecular 单分子 (involving one reactant 反应物 )

For example

NO2(g) + hv → NO(g) + O(g) 太阳辐射 nitrogen solar nitric atomic dioxide radiation oxide oxygen wavelength 420nm

Chemical kinetic reactions are usually bimolecular 双分子

Thermal decomposition reaction 热分解反应 .N2O5(g) + M → NO2(g) + NO3(g) + M

dinitrogen nitrogen nitrate pentoxide dioxide radical

M can be any molecule that provides collisional energy 碰撞能量 .

Isomerization reaction 异构化反应

H2-C-O-O* + M → HO*-CH=O + M

excited 激发态 excited formicCriegee biradical acid

Isomers 异构体 :chemical compound which has the same number and kind of atoms as another but differs in structural arrangement 原子排列

M can be any molecule that provides collisional energy 碰撞能量 .

Collision reaction 碰撞反应

. . CH4(g) + OH(g) → CH3(g) + H2O(g)

methane hydroxyl methyl water radical radical vapor

Termolecular 三分子 collision reactions are rare 稀有 because the probability 概率 that three gases collide simultaneously 同时发生 and change form is not large

.NO2(g) + NO3(g) + M N2O5(g) + M

nitrogen nitrate dinitrogendioxide radical pentoxide

M is any molecule whose purpose 目的 is to carry away energy released 释放 during the reaction.

Chapter 2The Sun, the Earth, and the evolution 进化 of the Earth’s atmosphere 太阳、地球 和大气的进化

2.4. SummaryThe sun formed from the condensation of the solar nebula 太阳星云 about 4.6 billion years ago (b.y.a) 46 亿年前 . Solar radiation 太阳辐射 incident on the Earth originates from the sun’s photosphere 光球 . The photosphere emits radiation with an effective temperature near 6,000 K (5,727 ). The solar ℃spectrum consists of UV 紫外线 , visible 可见光谱 , and near–IR近红外线 wavelength regimes. The Earth formed from the same nebula as the sun. Most of the Earth’s growth was due to asteroid 小行星 and meteorite 陨石 bombardment 碰撞 .

1 billion = 10 亿 = 1,000,000,000 = one thousand million

2.4. Summary (continued)

The composition of the Earth, percentage-wise, is similar to that of stony meteorites. Dense compounds 高密度 and compounds with high melting points 高熔点 settled to the center of the Earth. Light compounds and those with low melting points became concentrated in the crust 地壳 . The first atmosphere of the Earth, which consisted of hydrogen氢 and helium 氦 , may have been swept away 吹掉 by an enhanced solar wind 太阳风 during early nuclear explosions核爆炸 in the sun. The second atmosphere, which resulted from outgassing 气体释出 , initially consisted of carbon dioxide, water vapor, and assorted gases 混合气体 .

2.4. Summary (continued) When microbes 微生物 first evolved 进化 , they converted carbon dioxide, ammonia 氨 , hydrogen sulfide 硫化氢 , and organic material 有机物 to methane 甲烷 , molecular nitrogen 氮 , sulfur dioxide 二氧化硫 , and carbon dioxide, respectively.

Oxygen-producing photosynthesis 光合作用 led to the production of oxygen 氧 and ozone 臭氧 . The presence of oxygen resulted in the evolution of aerobic respiration 需氧呼吸 , which led to a more efficient means of producing molecular nitrogen, the major constitutent 要素 in today’s atmosphere (80% by volume).

2.1. The Sun and its Origin 太阳的诞生

About 15 b.y.a.(150 亿年前 ), all mass in the known universe 宇宙 may have been compressed 压缩 into a single point, estimated to have a density 密度 of 109 kg m-3 and a temperature of 1012 K. With the ‘Big Bang 大爆炸’ , this point of mass exploded, ejecting 弹射出 material to all directions. Aggregates 聚集物 of ejected material collapsed 压缩 gravitationally 引力 to form the earliest 最早期 stars 恒星 ;. When temperatures in the cores 中心 of early stars reached 10 million K, nuclear fusion 核聚变 of hydrogen into helium and higher elements began, releasing释放 energy that powered the stars. As early stars aged, they ultimately exploded, ejecting stellar 星形的 material into space.

About 4.6 b.y.a., some interstellar material aggregated to form a cloudy mass, the solar nebula 太阳星云 . The composition of the solar nebula was the same as that of 95 percent of the other stars in the universe. Gravitational collapse of the solar nebula resulted in the formation 形成 of sun

2.2. Spectra 光谱 of the radiation 辐射 of the Sun and the Earth

Life on Earth 地球上的生命 would not have evolved 进化 to its present state without heating (energy) by solar radiation.

Radiation 辐射 is the emission 发射 or propagation 传播 of energy in the form of a photon 光子 or electromagnetic wave 电磁波 .

A photon is a particle or quantum of energy 量子能量 that has no mass 没有质量 , no electric charge 没有电荷 , and an indefinite lifetime 无尽生命 .

An electromagnetic wave is a disturbance 扰乱 traveling through a medium 媒体 , such as air or space 宇宙空间 (vacuum真空 ), that transfer energy from one object to another without permanently 永久性 displacing 取代 the medium itself.

A blackbody 黑体 is a body that absorbs 吸收 all radiation incident on it but it also emit 发射 radiation with 100% efficiency.

Both the Sun and Earth are very close 接近 to blackbodies as no bodies are true blackbodies.

波长

伽马射线

可见光

红外线 微波

无线电波

2.3. Primordial Evolution 原始进化 of the Earth and its Atmosphere

球核心的内层 2900-6371 km

iron 铁

地幔 50 – 2900 kmmagnesium 镁

地壳 0 – 50 km

silicate 硅酸盐

Fig. 2.8. Timeline of evolution on the Earth 地球进化年历表

billionyears ago

To date迄今

2.3.2. Prebiotic atmosphere 有生命前的大气

The temperature on Earth was still very high, the atmosphere contained mainly molecular hydrogen, methane, ammonia, molecular nitrogen and hydrogen sulfide.

2.3.3. Biotic atmosphere before oxygen 无氧前的有生命大气

Abiotic synthesis 非生物合成 is the process by which life is created from chemical reactions and electric discharges.

Phototrophs 光合菌 are organisms that obtain their energy from sunlight, such as some sulfur bacteria 硫磺菌 .

CO2(g) + 2H2S + hv → CH2O(aq) + H2O(aq) + 2S(g) hydrogen sunlight carbohydrate sulfur

sulfide 碳水化合物

Lithotrophs 无机氧化生物 are organisms that obtain their energy from oxidation of inorganic compounds such as carbon dioxide, hydrogen, hydrogen sulphide, such as some methanogenic bacteria. Methane 甲烷 4H2(g) + CO2(g) → CH4(g) + 2H2O(g) (anaerobic repiration 无氧呼吸 )

Conventional heterotrophs 异养生物 are organisms that obtain their energy from oxidation of organic compounds, such as humans.

fermentation 发酵 C6H12O6(aq) → 2C2H5OH(aq) + CO2(g) glucose ethanol 乙醇

Carbon sources 碳源 for organismsAutotrophs 自养生物 are organisms that obtain their carbon from carbon dioxide.

Photoautotrophs 光合自營性菌 derive their energy from sunlight and carbon from carbon dioxide, such as all green plants.

photosynthesis 光合作用 6CO2(g) + 6H2O(aq) + hv → C6H12O6(g) + 6O2(g)

Lithotrophic autotrophs derive their energy and carbon from inorganic material.

Lithotrophic heterotrophs derive their energy from inorganic material but their carbon source from organic material.

2.3.5. Aerobic respiration 需氧呼吸

C6H12O6(g) + 6O2(g) → 6CO2(g) + 6H2O(aq)

Oxygen cycle 氧循环

The Oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs:

the atmosphere (air), the total content of biological matter within the biosphere (the global sum of all ecosystems), and the lithosphere

(Earth's crust). Failures in the oxygen cycle within the hydrosphere (the combined mass of water found on, under, and over the surface

of a planet) can result in the development of hypoxic zones. The main driving factor of the oxygen cycle is photosynthesis, which is

responsible for the modern Earth's atmosphere and life.

2.3.6. Nitrogen cycle 氮循环nitrogen fixation 固氮作用ammonification 氨化作用nitrification 硝化作用denitrification 反硝化作用

Most nitrogen is found in the atmosphere. The nitrogen cycle is the process by which atmospheric nitrogen is converted to ammonia or nitrates.           Nitrogen is essential to all living systems. To become a part of an organism, nitrogen must first be fixed or combined with oxygen or hydrogen. Nitrogen is removed from the atmosphere by lightening and nitrogen fixing bacteria. During electrical storms, large amounts of nitrogen are oxidized and united with water to produce an acid which is carried to the earth in rain producing nitrates. Nitrates are taken up by plants and are converted to proteins.           Then the nitrogen passes through the food chain from plants to herbivores to carnivores. When plants and animals eventually die, the nitrogen compounds are broken down giving ammonia (ammonification). Some of the ammonia is taken up by the plants; some is dissolved in water or held in the soil where bacteria convert it to nitrates (nitrification). Nitrates may be stored in humus or leached from the soil and carried to lakes and streams. It may also be converted to free nitrogen (denitrification) and returned to the atmosphere