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” Principle Strata 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 reaksi konversi hidrokarbon menjadi spesies teroksidasi, menghasilkan ozon dan partikel (penggunaan fossil fuel menunjukkan kenaikan konsentrasi zat ini di northen hemisfer dekat permukaan) Radikal hidroksil spesies reaktif yang utama di troposfer dan meremove sebagian besar jenis polutan di udara (terbetuk dari kombinasi ozon dan uap air, dengan radiasi sinar matahari) CO reagen penting di atmosfer diemisikan langsung dari pembakaran kondisi kurang oksigen atau dihasilkan di atmosfer melalui oksidasi virtual seluruh hydrokarbon. Kira-kira ¾ OH atmosfer akan bereaksi dengan CO menghasilkan 1/6 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 aryl compounds 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
v = c/
O +O2
• 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
visible
E = hv
Red Orange Yellow Green Blue Violet Near UV Far UV
700 620 580 530 470 420 400-200 200-50
Energy/kJ mol-1 170 190 210 230 250 280 300-600 600-2400
The Troposphere
Stratosphere, upper atmosphere
10-16 k m, -56ūC Troposphere O2, N2, Ar, CO2, trace gas es Vapor NO 2 + h NO + O Photoche mical reactions
H2O Droplets
Air pollutan ts Particle s
Temperature invers ion
We athe r
The Stratosphere (Cont.) High-ene rgy ultraviolet, wavelength less than 100 nanometers, pen etrating to arou nd 200 k m altitude Ultraviolet above 330 nanometers, visible light, infrared, pen etrating through the stratos phere and to Earth Õs su rface
Ultraviolet be tween 200-330 nanometers pe netrating to around 50 k m altitude
~ 50 k m, -2ūC O2 + h O + O Stratosphe re O2 + O O3 O3 + h O2 + O (filtration of ultraviolet radiation ) 10-16 k m, -56ūC
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 bronchiolitis fibrosa 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, SO42-, 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
CHEMICAL MECHANISMS solar radiation, O2
NO2
O3
NO
HNO3 CO2
wet dep O3
OH
O2
HO2
CO
solar rad.
H2O2
• Analzye mechanism using principles of chemical kinetics
wet dep
CHEMICAL KINETICS
• Chemical kinetics A study of the rate at which chemical reactions take place and the detailed chemical mechanism by which they occur • Rules Mass 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- CO32- + H+
CH4 Oxidation Scheme CH4 + OH CH3O2 + CH3O + HO2 +
(+O2) CH3O2 + H2O NO CH3O + NO2 O2 HO2 + HCHO 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.
Chemistry of ozone formation sunlight
O3
O2
sunlight NO2
NO
OH
HO2
RO2
RO
oxidation product
VOC O2
NO
NO2
O2
O3
sunlight
O2
General VOC oxidation scheme O3 + h O1D + O 2 O 1 D + H2 O 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)
SIKLUS KARBON 44
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
