reaksi-reaksi atmosfer dan dampak pencemaran udara...

Reaksi-reaksi atmosfer dan

Dampak pencemaran udara

terhadap kesehatan dan

lingkungan

Kuliah Minggu VIII

Laboratorium Pencemaran Udara dan Perubahan Iklim (LPUPI)

Jurusan Teknik Lingkungan FTSP ITS

Komposisi Atmosfer

The atmosphere consists of the thin layer of mixed gases covering the earth’s surface. Exclusive of water, atmospheric air is 78.1% (by volume) nitrogen, 21.0% oxygen, 0.9% argon, and 0.03% carbon dioxide.

Normally, air contains 1-3% water vapor by volume; large variety of trace level gases at levels below 0.002% (neon, helium, methane, krypton, nitrous oxide, hydrogen, xenon, sulfur dioxide, ozone, nitrogen dioxide, ammonia, and carbon monoxide)

Pembagian Atmosfer berdasarkan

temperatur troposphere extending in altitude from the earth’s surface to approximately 11 -16

kilometers (km), homogeneous composition of major gases (results from constant mixing by circulating air masses); decreasing temperature with increasing altitude The temperature of the troposphere ranges from an average of 15°C at sea level to an average of -56°C at its upper boundary. the water vapor content of the troposphere is extremely variable because of cloud formation,

precipitation, and evaporation of water from terrestrial water bodies.

stratosphere 11 km to approximately 50 km. The average temperature of the stratosphere increases from -56°C at its boundary with the troposphere to –2°C at its upper boundary. The reason for this increase is absorption of solar ultraviolet energy by ozone (O3) in the stratosphere

Mesosphere immediately above the stratosphere results in a further temperature decrease to about –92°C at an altitude around 85 km.

thermosphere, in which the highly rarified gas reaches temperatures as high as 1200°C by the absorption of very energetic radiation of wavelengths less than approximately 200 nm by gas species in this region

Stratifikasi

Atmosfer

dan

Spesies

yang

dipengaruhi

fotoreaksi

“Lee Chateleur” PrincipleStrata Atmosfer Sifat Fisik dan Kimia

Troposphere Makin tinggi tekanan menurun,

temperatur menurun. Reaksi makin

cepat ke arah exotermis, dan

pemecahan molekul.

Stratosphere Makin tinggi tekanan makin turun,

temperatur makin naik. Reaksi kimia

makin cepat ke arah endotermis dan

pemecahan molekul.

Mesosphere Makin tinggi tekanan makin rendah

dan suhu makin rendah. Reaksi

molekul menjadi lebih sulit karena

tekanan terlalu rendah, tumbukan

antar molekul makin jarang.

Thermosphere Makin tinggi tekanan makin rendah,

suhu extrem makin tinggi, rekasi

makin sulit terjadi.

Beberapa parameter kunci pada

kinetika dan reaksi atmosfer Molekul stabil CO2, N2, O2, dimana O2 merupakan dasar dari

kimia ozon (O3)

Oksida nitrogen sebagai katalis di troposfer dalam deret reaksikonversi hidrokarbon menjadi spesies teroksidasi, menghasilkanozon dan partikel (penggunaan fossil fuel menunjukkan kenaikankonsentrasi zat ini di northen hemisfer dekat permukaan)

Radikal hidroksil spesies reaktif yang utama di troposfer danmeremove sebagian besar jenis polutan di udara (terbetuk darikombinasi ozon dan uap air, dengan radiasi sinar matahari)

CO reagen penting di atmosfer diemisikan langsung daripembakaran kondisi kurang oksigen atau dihasilkan di atmosfermelalui oksidasi virtual seluruh hydrokarbon.

Kira-kira ¾ OH atmosfer akan bereaksi dengan CO menghasilkan1/6 CO2 di atmosfer

ENERGY BALANCE ATMOSFIR

BUMI

Proses

yang

terjadi

pada

spesies

gas di

atmosfer

Major atmospheric Chemical

Process

Gas-gas yang berperan dalam

reaksi atmosfer Gaseous atmospheric chemical species fall into the following

somewhat arbitrary and overlapping classifications: Inorganic oxides (CO, CO2, NO2, SO2),

oxidants (O3, H2O2, HO. radical, HO2. radical, ROO. radicals, NO3),

reductants (CO, SO2, H2S),

organics (also reductants; in the unpolluted atmosphere, CH4 is the predominant organic species, whereas alkanes, alkenes, and arylcompounds are common around sources of organic pollution),

oxidized organic species (carbonyls, organic nitrates),

photochemically active species (NO2, formaldehyde),

acids (H2SO4, HNO3, etc),

bases (NH3),

salts (NH4HSO4,), and

unstable reactive species (electronically excited NO2, HO• radical)

solid and liquid particles in atmospheric

aerosols and clouds play a strong role in

atmospheric chemistry as sources and sinks

for gas-phase species, as sites for surface

reactions (solid particles), and as bodies for

aqueous-phase reactions (liquid droplets).

Atmospheric

Chemistry starts with sunlight

O3 O+O2

E = hv

• Breaking chemical bonds

requires energy

• Sunlight has energy

• If sufficient energy is deposited

in the bond, then it will break

• O3 has a bond energy of ~105

kJ mol-1

v = c/

Energy/kJ mol-1

Red 700 170

Orange 620 190

Yellow 580 210

Green 530 230

Blue 470 250

Violet 420 280

Near UV 400-200 300-600

Far UV 200-50 600-2400vi

sible

The Troposphere

10-16 km, -56ūC

Temperatureinvers ion

O2, N2, Ar, CO2, trace gases

NO2 + h NO + O

Photoche mical reactions

Stratosphere, upper atmosphere

Troposphere

We athe r

H2O

Vapor

Droplets

Particle s

Air pollutants

The Stratosphere (Cont.)

10-16 km, -56ūC

O2 + h O + O

O2 + O O3

O3 + h O2 + O(filtration of ultra- violet radiation)

Stratosphe re

~ 50 km, -2ūC

Ultraviolet be tween 200-330nanometers pe netrating toaround 50 km altitude

High-ene rgy ultraviolet, wave-length less than 100 nanometers,penetrating to around 200 kmaltitude Ultraviolet above 330 nano-

meters, visible light, infrared,penetrating through the strat-osphere and to EarthÕs surface

Reaksi fotokimia

Penyerapan energi cahaya (spektrum) oleh spesies kimia, khususnya radiasi ultraviolet, dari matahari, dapat menyebabkan reaksi kimia

Adanya katalis, akan menyebabkan reaksi fotokimia dapat terjadi pada suhu/energi lebih rendah

Reaksi ini dapat digunakan untuk prediksi keberadaan dan nasib (fate) spesies kimia di atmosfer

Nitrogen dioxide, NO2, is one of the most

photochemically active species found in a

polluted atmosphere and is an essential

participant in the smog-formation process.

A species such as NO2 may absorb light of

energy hv, producing an electronically

excited molecule.

Proses reaksi fotokimia

Loss of energy to another molecule or atom (M) by

physical quenching, followed by dissipation of the

energy as heat

Ion dan Radikal di Atmosfer Salah satu karakteristik atmosfer bagian atas adalah adanya ion-ion

positif maupun negatif yang stabil (ionosphere > 50 km)

Producer ion-ion yang utama adalah reaksi yang diakibatkan oleh cahaya ultraviolet intensitas tinggi

Di troposphere juga terbentuk ion-ion, pada fenomena titik-titik air yang mengalami gesekan, kompresi selama presipitasi akibat fenomena turunnya massa udara dingin atau karena angin panas yang kuat. (Fenomena Foehn/Sharav/Santa Ana)

energetic electromagnetic radiation in the

atmosphere may produce atoms or groups

of atoms with unpaired elect rons called

free radicals

Proses Pembentukan Radikal (inisiasi)

Proses Reaksi dengan senyawaan netral

(propagasi)

Proses reaksi radikal dengan radikal

(terminasi)

Radikal Hodroksil dan

Hidroperoksil di Atmosfer

Removing OH radikal dari Atmosfer

Reaksi Kimia dan Biokimia

Atmosfer

NOx sinks & transport

NOx lifetime ~1 day

NOx sinks – primarily

HNO3

HNO3 is water soluble

PAN allows locally produced NOx to be

transported on global scales

Kelas utama bahan pencemar di udara

Kelas Contoh

Carbon oxides Carbon monoxide (CO), Cabon dioxide (CO2)

Sulfur oxides Sulfur dioxide (SO2), Sulfur trioxide (SO3)

Nitrogen oxides Nitric oxide (NO), nitrogen dioksida (NO2), nitrous oxide (N2O) (NO

dan NO2 sering tergabung bersama dan diberi label NOx

Volatile Organic Compound (VOCs) Methane (CH4), propane (C3H8), chlorofluorocarbons (CFCs)

Suspended particulate matter (SPM) Partikel padat (debu, jelaga, asbestos, timbal, nitrat dan garam

sulfat), butiran air (asam sulfat, PCBs, dioxines dan pestisida)

Photochemical oxidants Ozon (O3), peroxyacyl nitrates (PANs), hydrogen peroxide (H2O2)

Radioactive substances Radon-222, iodine-131, strontium-90, plutonium-239

Hazardous air pollutants (HAPs), yang

dapat menyebabkan gangguan

kesehatan seperti kanker,

gangguan sistem saraf dan cacat

kelahiran

Carbon tetrachloride (CCl4), methyl chloride (CH3Cl), chloroform

(CHCl3), benzene (C6H6), etylene dibromide (C2H2Br2),

formaldehyde (CH2O2).

General description of a chemical mechanism

Oxygen exchange among the atmosphere,

geosphere, hydrosphere, and biosphere

FENOMENA OKSIGEN DAN NITROGEN

N2 and O2 are by far the most abundant gases in the atmosphere.

Crucial importance of the stratospheric layer of ozone, O3

Oxygen reacts with atmospheric chemical species.

• Through action of intermediate species, particularly hydroxyl radical, HO

• SO2 is converted to H2SO4

• CO is converted to CO2

Atmospheric oxygen comes from photosynthesis

CO2 + H2O + h {CH2O} + O2 (8.4.2)

where {CH2O} is a generic formula representing biomass

Nitrogen in the atmosphere

Atmospheric N2 is very unreactive

Most important reaction of N-containing species in the atmosphere

NO2 + h NO + O (8.4.3)

Reactive O atom initiates many tropospheric photochemical reactions

Chemical Processes on and in Atmospheric Particles

POLLUTANT GASEOUS OXIDES

Carbon Monoxide

Toxic to humans by binding to blood hemoglobin and preventing the hemoglobin from transporting oxygen from the lungs to other tissues.

Catalytic destruction in auto exhausts:

2CO + O2 2CO2 (8.6.1)

Modern automobile engines use computerized control of engine operating parameters along with exhaust catalysts to control carbon monoxide emissions.

Pollutant Gaseous Oxides (Cont.)

Sulfur Dioxide

From several natural and pollutant sources

Direct effects

• On people with respiratory problems • On plants

Most important indirect effect is atmospheric sulfuric acid formation

2SO2 + O2 + 2H2O 2H2SO4 (8.6.2)

Avoiding sulfur dioxide pollution by not using sulfur-containing fuels (coal)

Fluidized bed combustion in a granular medium of CaO that absorbs SO2

CaO + SO2 CaSO3 (8.6.3)

Scrubbing with substances that absorb sulfur dioxide from stack gas

Ca(OH)2 + SO2 CaSO3 + H2O (8.6.4)

Green Chemistry and Sulfur Dioxide

Sulfur is a valuable raw material required in the manufacture of sulfuric acid, one of the largest volume chemicals made.

Hydrogen sulfide, H2S, can be used to make sulfur dioxide.

In the Kalundborg, Denmark, industrial ecosystem, sulfur dioxide scrubbed from stack gas is oxidized

CaSO3 + 1/2O2 + 2H2O CaSO4.2H2O (8.6.5)

and used to make gypsum for wallboard.

Nitrogen Oxides in the Atmosphere

Nitrous oxide (N2O), colorless, odorless, nitric oxide (NO), and pungent-smelling, red-brown nitrogen dioxide (NO2) occur in the atmosphere.

Nitrous oxide generated by bacteria

In the stratosphere: N2O + h N2 + O (8.6.6)

Both NO and NO2, collectively designated as NOx, are produced from natural sources, such as lightning and biological processes, and from pollutant sources.

Pollutant concentrations can become too high locally and regionally.

In the internal combustion engine,

N2 + O2 2NO (8.6.7)

Combustion of fuels that contain organically bound nitrogen also produces NO.

Atmospheric chemical reactions convert some of the NO emitted to NO2.

NO2 in the Atmosphere

Electromagnetic radiation below 398 nm causes

NO2 + h NO + O (8.6.8)

• Produces highly reactive O atoms

• O atoms can participate in a series of chain reactions through which NO is converted back to NO2, which can undergo photodissociation again to start the whole cycle over.

NO2 more toxic than NO

• Exposure to 100-500 ppm of NO2 causes a lung condition called bronchiolitisfibrosa obliterans

• Exposed plants may suffer decreased photosynthesis, leaf spotting, and breakdown of plant tissue.

Reducing release of NO from combustion sources

• Limiting excess air so that there is not enough excess oxygen to produce NO

• Exhaust catalytic converters reduce NOx emissions from automobile exhausts.

Halogen Gases in the Atmosphere

Gaseous chlorine, fluorine, and volatile fluorides are uncommon air pollutants, but very serious where they occur.

Elemental chlorine, Cl2, is widely produced and distributed as a water disinfectant, bleach, and industrial chemical.

Accidental releases of Cl2 have killed people

Hydrogen chloride, HCl, from accidental releases and by reaction of reactive chlorine-containing chemicals, such as SiCl4,

SiCl4 + 2H2O SiO2 + 4HCl (8.8.3)

HCl gas from combustion of polyvinylchloride (PVC) plastic

Exists as droplets of hydrochloric acid

Elemental fluorine (F2) and hydrogen fluoride, both highly toxic, are rarely released to the atmosphere.

Gaseous silicon tetrafluoride, SiF4, can be released when fluorspar (CaF2) reacts with sand (SiO2):

2CaF2 + 3SiO2 2CaSiO3 + SiF4 (8.8.4)

Sulfur hexafluoride, SF6, is astoundingly unreactive and a powerful greenhouse warming gas

Hydrogen Sulfide, H2S

Hydrogen sulfide, H2S is as toxic as hydrogen cyanide.

From geothermal sources, the microbial decay of organic sulfur compounds, and the microbial conversion of sulfate, SO4

2-, to H2S when sulfate acts as an oxidizing agent in the absence of O2

Wood pulping processes can release hydrogen sulfide.

H2S is a common contaminant of petroleum and natural gas.

Poza Rica, Mexico, incident in 1950 killed 22 people

H2S is phytotoxic (harms or kills plants)

H2S forms a black coating of copper sulfide, CuS, on copper roofing which weathers to CuSO4 3Cu(OH)2.

H2S oxidizes to SO2.

COS and CS2, occur in the atmosphere

CO2: THE ULTIMATE AIR POLLUTANT?

Carbon dioxide, CO2, is a normal essential constituent of the atmosphere.

Levels now about 380 parts per million by volume and increasing by at least 1 ppm/year

Potential greenhouse effect

Evidence of warming during 1980s, 1990s, early 2000s

Other gases such as N2O and CH4 can cause greenhouse warming

NO2 NO

OH HO2

CO

O3

O2

solar radiation, O2

H2O2solar rad.

wet dep

HNO3

wet depCO2

CHEMICAL MECHANISMS

O3

• Analzye mechanism using principles of chemical kinetics

CHEMICAL KINETICS

• Chemical kineticsA study of the rate at which chemical reactions take place and the detailed chemical mechanism by which they occur

• RulesMass balance integrity of atoms is preserved in a chemical reactions number of atoms of each each element on each side of the reaction must balance

CO + 2O2 CO2 + O3

Charge conservation electrons are conserved in chemical reactions net charge of reactants are equal to net charge of products

HCO3- CO3

2- + H+

CH4 + OH (+O2) CH3O2 + H2O

CH3O2 + NO CH3O + NO2

CH3O + O2 HO2 + HCHO

HO2 + NO OH + NO2

HCHO + OH (+O2) HO2 + CO + H2O

HCHO + h H2 + CO

HCHO + h (+2O2) 2HO2 + CO

Note:

2 × (NO NO2) conversions

HCHO formation provides a route to HO2 radical formation.

CH4 Oxidation Scheme

Chemistry of ozone formation

VOCoxidation

product

OH HO2

RO2 RO

NO NO2

NONO2

O2 O2

sunlight O3O2

sunlight

O2

O3

sunlight

General VOC oxidation scheme

O3 + h O1D + O2

O1D + H2O 2OH

OH + RH (+O2) RO2 + H2O

RO2 + NO NO2 + RO

RO + O2 HO2 +R’CHO

HO2 + NO OH + NO2

NO2 + h NO + O; O + O2 O3

OVERALL

NOx + VOC + sunlight ozone

The same reactions can also lead to formation of secondary organic aerosol

(SOA)

44

SIKLUS KARBON

Tugas

Reaksi Asam Basa Atmosfer

Reaksi Oksigen di Atmosfer

Reaksi Nitrogen di Atmosfer

Karbon dioksida di Atmosfer

Water (air) di Atmosfer

Reaksi Fotokimia di Atmosfer