Tropospheric Chemistry and Ground Level Ozone

Transcription

1 Tropospheric Chemistry and Ground Level Ozone

2 Tropospheric Chemistry: The Formation of Ground Level Ozone Ozone Modeling and Air Quality Role of Trees in Ozone Formation Reading: Chapters 4&6 Environmental Chemistry, G. W. vanloon. S. J. Duffy

3 The Troposphere

4 The Troposphere

5 1s 100s 1hr 1day 1yr 10yrs 100yrs Time Scale Micro- Scale Urban or Local Scale Regional or Mesoscale Synoptic or Global Scale Long-lived Species CFC s N 2 O Moderately Long- Lived Species SO 2 CO Aerosols Trop O 3 CH 4 CH CH 3 Br 3 CCl 3 Inter- Hemispheric Mixing Time Intra- Hemispheric Mixing Time H 2 O 2 NO x DMS Boundary Layer Mixing Time C 3 H 6 C 5 H 8 Short-lived Species CH 3 O 2 HO 2 NO 3 OH 1m 10m 100m 1km 10km 100km 1000km 10,000km Space Scale

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7 Atmospheric Fate of Species Water Soluble Readily Photolyzed Multiple Bonds Labile Hydrogen Inert yes yes yes yes yes Rain-out Free Radicals Transported to Stratosphere

8 Tropospheric Ozone Natural background due to Troposphere Stratosphere exchange is ppb Often observe Ozone levels >120 ppb near urban centers

9 Photochemical Smog Event 1.0 Aldehydes Concentration (Arb. Units) Hydrocarbons NO NO 2 O Time of Day

10 Photochemistry of O 3 O 3 + hv O( 3 P) + O 2 ground state, unexcited, atoms O( 3 P)+ O 2 O 3 recombination

11 The Formation of OH O 3 + hv O( 1 D) + O 2 excited atoms 90% O( 1 D)+ N 2,O 2 O( 3 P)+ N 2,O 2 quenching 10% O( 1 D)+ H 2 O OH + OH

12 The Formation of OH 0.12 ] [ ] [ ] [ ] [ )] ( ][ [ )] ( ][ [ )] ( ][ [ )] ( [ )] ( ][ [ )] ( [ M k O H k M k O H k D O M k D O O H k D O M k dt D O d D O O H k dt D O d q r q r q r q r

13 Photochemistry of O 3 O O 3 3 Hartley Band hv O hv O 2 2 ( ( 1 3 g g 1 ) O( D) ) O( 3 P) Absorption Cross Section [cm 2 ] Huggins Band (>320nm) O3 hv O2 ( g or g ) O( D) Chappius Band 3 3 O3 hv O2 ( g ) O( P) Wavelength (nm)

14 Quantum Yields i i a b a i absorbed photons of total formed atoms P O of D O O h O P O O h O absorbed photons of total i process by proceeding molecules excited of 1.0 # ) ( # ) ( ) ( # #

15 1.0 Photochemistry of O 3 O( 1 D) Quantum Yield Wavelength (nm)

16 10 16 Actinic Flux Actinic Flux (photons s -1 cm -2 ) km Wavelength (nm)

17 The Formation of OH O 3 + hv O( 1 D) + O 2 O( 1 D)+ H 2 O OH + OH Diurnal cycle Average daytime concentration [OH] ~ 1x10 6 molecules cm -3

18 The Role of NOx N 2 + O 2 NO + NO combustion 2500 K NO + O 3 NO 2 + O 2 destruction of O 3 NO, NO 2 are referred to as NOx

19 The Role of NOx NO 2 + hv O( 3 P) + NO ground state atoms O( 3 P) + O 2 O 3 formation of O 3

20 Other Sources of NOx Ammonia Ocean Stratosphere Fossil Fuel Soils Lightning Biomass Burning

21 Ozone Clean Atmosphere O 2 NO NO 2 OH HONO 2 NO x emissions Ozone O 2 deposition

22 Ozone The Role of VOC s O 2 NO NO 2 OH HONO 2 NO x emissions RO 2 RO deposition OH O 2 VOC emissions

23 Hydrocarbon Oxidation -alkanes RH + OH R + H 2 O hydrogen abstraction R + O 2 RO 2 dioxygen addition peroxy radicals RO 2 + NO RO + NO 2 oxygen abstraction

24 Hydrocarbon Oxidation -alkanes RO + NO 2 RCHO + HOO formation of aldehyde HOO + NO NO 2 + OH regeneration of NO 2

25 Ozone Clean Atmosphere O 2 NO NO 2 OH HONO 2 NO x emissions Ozone O 2 deposition

26 Ozone The Role of VOC s O 2 NO NO 2 OH HONO 2 NO x emissions RO 2 RO deposition OH O 2 VOC emissions

27 Secondary Reactions:PAN Formation CH 3 CHO + OH CH 3 CO + H 2 O CH 3 CO + O 2 CH 3 C(O)O 2 acetylperoxy CH 3 C(O)O 2 + NO 2 CH 3 C(O)OONO 2 peroxyacetic nitric anhydride (PAN)

28 Photochemical Smog Species Concentration mg m -3 Polluted Areas Unpolluted Areas CO 10,000-30,000 <200 NO <20 Hydrocarbons 600-3,000 <300 (not Methane) Ozone <5 PANs <5

29 VOCs in Taipei City Species Concentration mg m -3 Toluene 980 m,p-xylene 910 Benzene 370 Ethylbenzene 310 Hexane 150 Heptane 130

30 Methane Oxidation CH 4 + OH CH 3 + H 2 O CH 3 + O 2 CH 3 O 2 CH 3 O 2 + NO CH 3 O + NO 2 CH 3 O + O 2 CH 2 O + HO 2

31 Formaldehyde Photolysis CH 2 O + hv (l<330 nm) HCO + H HCO + O 2 HO 2 + CO CO + HO CO 2 + H

32 Hydrocarbon Oxidation RH R OH O 2 NO RO 2 NO OH HO 2 RONO 2 hv, RO hv ROOH OH O 2, R CHO OH CO 2 + H 2 O

33 Alkene Oxidation OH RR C=CR R + OH RR C -CR R OH RR C -CR R + O 2 OH RR C-CR R O 2

34 Aromatic Oxidation OH H +. OH. OH H OH H OH. + O 2 + HO 2. O 2

35 Tropospheric Chemistry: The Formation of Ground Level Ozone Ozone Modeling and Air Quality Role of Trees in Ozone Formation Reading: Chapters 4&6 Environmental Chemistry, G. W. vanloon. S. J. Duffy

36 Primary vs. Secondary Air Pollutants: Primary pollutants: released directly from sources. Ex. CO, SO 2, NOx Secondary pollutants: formed through chemical reactions of the primary pollutants. Ex. O 3

37 HO 2 Radical: Interconversion of OH and HO 2 HO 2 + NO OH + NO 2 OH + RCH 3 H 2 O + RCH 2 RCH 2 + O 2 RCH 2 OO RCH 2 OO + NO NO 2 + RCH 2 O RCH 2 O + O 2 RCHO + HO 2

38 Half-life for Reaction with OH and NO 3 Molecule OH NO 3 n-butane 5 days 205 days acetylene 14 days 188 days toluene 2 days 138 days formaldehyde 1.2 days 16 days NO 3 reaction rates cm 3 s -1 OH reaction rates cm 3 s -1

39 Reduce Hydrocarbon Emission or Reduce Nox Emissions? Control Strategies

40 Number of Days Exceeding the Ozone Standard Dallas/Fort Worth Tyler/Longview El Paso Beaumont/ Port Arthur Houston/Brazoria/ Galveston San Antonio Austin Corpus Christi Note: Totals include only state and local governmental ozone monitoring sites, not private networks. Source: Texas Natural Resource Conservation Commission, Data Management and Analysis Division, 1995.

41 Control Strategies for Ozone Control of VOCs General too abundant to be brought low enough to be the limiting factor. In certain areas, VOCs from biological sources could be significant. Control of NOx Difficult to control as efficient energy conversion requires high combustion temperature.

42 Photochemical Smog Event 1.0 Aldehydes Concentration (Arb. Units) Hydrocarbons NO NO 2 O Time of Day

43 NATIONAL AMBIENT AIR QUALITY STANDARDS (NAAQS) POLLUTANT AVERAGING PERIOD PRIMARY NAAQS NOTES Ozone 1-Hour ppm 8-Hour ppm Carbon Monoxide 1-Hour ppm 8-Hour 9.50 ppm Sulfur Dioxide Annual 0.03 ppm 24-Hour 0.14 ppm Nitrogen Dioxide Annual ppm Respirable Particulate Matter 24-Hour mg/m 3 (PM10) Annual mg/m 3 Lead Quarter 1.55 mg/m 3 Source: Texas Air Control Board, Texas Air Control Board Fact Sheets: National Ambient Air Quality Standards (Austin: TACB, 1993), 3.

44 1992 AIR EMISSION OF TOXICS IN MILLIONS OF POUNDS IN TEXAS, SELECTED STATES AND THE U.S. FUGITIVE AIR EMISSIONS POINT AIR EMISSIONS TOTAL Texas Tennessee Alabama Ohio Louisiana Indiana \ 85.9 Top Six States Wyoming New Mexico North Dakota Nevada Vermont Hawaii Bottom Six TOTAL U.S , ,845 Source: Environmental Protection Agency, 1992 Toxics Release Inventory: Public Data Release (Washington, DC: U.S. Governmental Printing Office, May 1994), Table 1-6.

45 High NOx Low VOC Ozone Isopleth Low NOx High VOC

46 High NOx Low VOC Ozone Isopleth Low NOx High VOC

47 Ozone Isopleth Does not include transport Does not include ozone production from previous days Does not include natural sources of hydrocarbons (NMOC)

48 Kill Trees or Reduce NOx?: Reducing Ground Level Ozone

49 Biogenic Non-Methane Organic Compounds (NMOC) Emissions Estimated 1150 Tg of carbon yr -1 from biogenic NMOCs is emitted worldwide NMOC emissions are ~10 times higher than anthropogenic NMOC emissions worldwide (~1.5 in North America)

50 Impact of Biogenic (non-methane,nmoc) Oxidation The contribution of NMOC oxidation to tropospheric O 3 formation is estimated to be approximately 75% in parts of the US Oxidation of natural hydrocarbons contributes ~20% of the global CO budget A significant contribution of submicron aerosol mass is organic matter of biogenic origin

51 Lifetime a for reaction with Biogenic NMOC OH NO 3 O 3 isoprene 1.4 hr 50 min 1.3 day camphene 2.6 hr 50 min 18 day 3-carene 1.6 hr 4 min 11 hr limonene 50 min 3 min 2.0 hr myrcene 40 min 3 min 50 min α-pinene 2.6 hr 5 min 4.6 hr β-pinene 1.8 hr 13 min 1.1 day sabinene 1.2 hr 3 min 4.6 hr β-caryophyllene 40 min 2 min 2 min longifolene 3.0 hr 50 min >33 day methanol 12 day 1 yr >4.5 yr 2-methyl-3-buten-2-ol 2.1 hr 4 day 1.7 day cis-3-hexen-1-ol 1.3 hr 2.1 hr 6 hr linalool 50 min 3 min 55 min 1,8-cineole 1.0 day 270 day >4.5 yr cis-3-hexenylacetate 1.8 hr 2.3 hr 7 hr 6-methyl-5-hepten-2-one 55 min 4 min 1.0 hr methyl vinyl ketone 6.8 hr >1.0 yr 3.6 day methacrolein 4.1 hr 14 day 15 day 3-methylfuran 1.5 hr 3 min 19 hr pinonaldehyde 2.9 hr 2.3 day >2.3 yr caronaldehyde 2.9 hr 1.9 day >2.3 yr sabinaketone 2.3 day 130 day >0.9 yr nopinone 10 hr camphenilone 2.3 day CH 4 lifetime: 10 years a With concentrations (molecule cm -3 ) of: OH, 12-hr daytime average of 2.0 x 10 6 ; NO 3, 12-hr nighttime average of 5 x 10 8 ; O 3, 24-hr average of 7 x

52 Abundance of Biogenic NMOCs Emissions alkenes 2.0% terpenes 30.9% isoprene 50.8% oxygenated 16.1% methanol 0.2% North American Continetial Biogenic NMOC Emissions weighted by OH Reactivity

53 North American Isoprene Emission isoprene emission (nmol m -2 s -1 )

54 Isoprene Oxidation

55 OH Initiated Oxidation of Isoprene The distribution of first generation products has been identified by numerous environmental chamber studies other species 30% methyl vinyl ketone + HCHO 32% organic nitrates 11% 3-methyl furan 4% methacrolein + HCHO 23%