Air Pollution-Tropospheric Ozone
Air Pollution-Tropospheric Ozone
Good ozone and bad ozone Stratospheric ozone protect lives on Earth from harmful effects of uv radiation Tropospheric ozone Causing respiratory distress and eye irritation Destroying plants Producing cracks in rubber Ozone is a strong oxidant reacts with molecules containing C=C double bonds, forming epoxides
Good Ozone and Bad Ozone • Stratospheric ozone protect lives on Earth from harmful effects of UV radiation. • Tropospheric ozone: – Causing respiratory distress and eye irritation – Destroying plants – Producing cracks in rubber Ozone is a strong oxidant, reacts with molecules containing C=C double bonds, forming epoxides
Two types of air pollutants: primary vs secondary Primary pollutants: released directly from sources Examples: CO, So2, NOX Secondary pollutants: formed through chemical reactions of the primary pollutants and the constituents of the unpolluted atmosphere in the air. Example: 03
Two types of air pollutants: primary vs. secondary • Primary pollutants: released directly from sources – Examples: CO, SO2, NOx • Secondary pollutants: formed through chemical reactions of the primary pollutants and the constituents of the unpolluted atmosphere in the air. – Example: O3
Formation of ozone No2 is capable of absorbing visible light(NO2+OH RO2+NO→NO2+RO (5) Net of(1)+(2)+(4):RO2+02→03+RO
Formation of ozone NO2 + hv → NO + O (1) O + O2 + M → O3 + M (2) NO + O3 → NO2 + O2 (3) NO2 + hv → NO + O (1) O + O2 + M → O3 + M (2) HO2 . + NO→ NO2 + OH (4) RO2 . + NO → NO2 + RO. (5) No net O3 formation O3 is formed Net of (1)+(2)+(4): RO2. + O2 → O3 + RO. NO2 is capable of absorbing visible light (<400 nm) to produce O
Sources of RO2: Oxidation of hydrocarbons RH+OH→R·+H20 R·+02÷RO2 A single organic radical can produce many peroxy radicals by successive rounds of O2 combination and fragmentation
Sources of RO2. : Oxidation of hydrocarbons RH + OH → R . + H2O R . + O2 → RO2. A single organic radical can produce many peroxy radicals by successive rounds of O2 combination and fragmentation
Example: Oxidation of carbon monoxide CO oH +o> CO, +HO HO+NO→>NO2+OH no t hy>NO +o Q+Q2+M→Q3+M Net: co+20+hv>CO+o The net reaction can be viewed as a catalytic oxidation of Co to co. Net formation of o, occurs
Example: Oxidation of carbon monoxide CO + .OH + O2 → CO2 + HO2 . HO2 . + NO → NO2 + .OH NO2 + hv → NO + O O + O2 + M → O3 + M Net: CO + 2 O2 + hv → CO2 + O3 The net reaction can be viewed as a catalytic oxidation of CO to CO2 . Net formation of O3 occurs
Example: Oxidation of methane CH4+ oH+02> CH300+H20 CH30O+NO→CH3O.+NO2 CH3O+O2→HCHO+HO2 HO2+No> OH+NO2 NO2 hv>NO+O(x O+O2+M→03+M(2x) Net: CH4+402 HCHo +H20+2 03 The net reaction is that for each mole of methane oxidized 2 moles of 03 is produced
Example: Oxidation of methane CH4 + .OH + O2 → CH3OO. + H2O CH3OO. + NO → CH3O. + NO2 CH3O. + O2 → HCHO + HO2. HO2. + NO → .OH + NO2 NO2 + hn → NO + O (2x) O + O2 + M → O3 + M (2x) Net: CH4 + 4 O2 → HCHO + H2O + 2 O3 The net reaction is that for each mole of methane oxidized, 2 moles of O3 is produced
Necessary ingredients for ozone formation Sunlight Production of o atom NOX(NO, NO2) Hydrocarbons (VOCs: volatile organic carbon Production of ro2, which reacts with No so that o3 could accumulate VOCS+ NOx hv>03+ other pollutants
Necessary ingredients for ozone formation • Sunlight • NOx (NO, NO2) • Hydrocarbons (VOCs: volatile organic carbon) VOCs + NOx + hn → O3 + other pollutants Production of O atom Production of RO2, which reacts with NO so that O3 could accumulate
Necessary ingredients for ozone formation CH4)+. OH +02>CH300+H20 VOC CH300+No > CH30+NO2 CH3O+02→HCHO+HO2 HO2NO→OH+NO2 NO2+hy)NO+O(2x) O+O2+M→O3+M(2x) Net: CH4+4 02 >HCHO +H20+2 03 Sunlight
Necessary ingredients for ozone formation CH4 + .OH + O2 → CH3OO. + H2O CH3OO. + NO → CH3O. + NO2 CH3O. + O2 → HCHO + HO2. HO2. + NO → .OH + NO2 NO2 + hn → NO + O (2x) O + O2 + M → O3 + M (2x) Net: CH4 + 4 O2 → HCHO + H2O + 2 O3 VOC Sunlight
Formation of oxidants other than o3 Formation of aldehydes(e.g. formaldehyde) Formation of pan (peroxyacetyl nitrate)and its analogs C +h +H. H3C H H3C H3C H3C PAN N H3C OONO ROO.+ No2> ROoNO2(peroxyalkyl nitrate
Formation of oxidants other than O3 • Formation of aldehydes (e.g. formaldehyde) • Formation of PAN (peroxyacetyl nitrate) and its analogs ROO. + NO2 → ROONO2 (peroxyalkyl nitrate) O C H3C H + hv O C H3C + H O C H3C + O2 O C H3C OO O C H3C OO + NO2 O C H3C OONO2 PAN
