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