Repetisjon kap 11
CO oxidation mechanism (low NO x ) Reaction chain CO + OH (+O 2 ) -> CO 2 + HO 2 R4+R6 HO 2 + O 3 -> OH + 2O 2 R13 Hvilke komponenter er katalysatorer her? Net: CO + O 3 -> CO 2 + O 2 OH&HO 2 catalysts in loss of O 3 in the troposphere in clean environments (low NO x ) CO oxidation mechanism (high NO x ) Reaction chain CO + OH (+O 2 ) -> CO 2 + HO 2 HO 2 + NO -> OH + NO 2 NO 2 + hν (+O 2 ) -> NO + O 3 Net: CO + 2 O 2 + hν -> CO 2 + O 3 R4+R6 R10 R11 Hvilke komponenter er katalysatorer her? OH&HO 2, NO&NO 2 catalysts in production of O 3 in the troposphere Termination HO 2 + HO 2 -> H 2 O 2 (soluble) + O 2 R7
Netto produksjon/tap av ozon? Konkurranse om HO 2 HO 2 + O 3 -> OH + 2O 2 HO 2 + NO -> OH + NO 2 R13 R10 k 13 [O 3 ] > k 10 [NO] [NO] < [O 3 ] k 13 /k 10 Netto ozon tap [NO]/[NO 2 ]= k 1 /(k 2 [O 3 ] ) [NO 2 ] = [NO x ] k 2 [O 3 ] / k 1 rask nullsykel Bestemt av [NO x ] < k 1 k 13 /(k 2 k 10 ) Netto ozon tap
GLOBAL BUDGET OF TROPOSPHERIC OZONE (MODEL) O 2 Present-day Preindustrial hn STRATOSPHERE 8-18 km TROPOSPHERE O 3 Chem prod in troposphere, Tg y -1 Transport from stratosphere, Tg y -1 4300 1600 400 400 Burden, Tg 360 230 Chem loss in troposphere, Tg y -1 Deposition, Tg y -1 4000 1600 700 400 Lifetime, days 28 42 O 3 hn, H 2 O NO 2 hn Deposition OH HO 2 NO CO, VOC H 2 O 2
CHAPTER 12: OZONE SMOG
GOOD AND BAD OZONE Good (UV shield) Bad (greenhouse gas) Good (OH source) Bad (smog) NO x = NO + NO 2 : nitrogen oxide radicals VOC (volatile organic compounds) = light hydrocarbons and substituted organic compounds
Local Pollution photochemical smog Emissions of primary components (NOx, CO and VOCs) Available sunlight is important more during summer than winter Metorlogical conditions. High pressure systems with subidence decrease vertical mixing of pollutants out of the boundary layer Topography can be important stops horizontal flow.
The Los Angeles basin.
The higher the wind velocity and the thicker the mixing layer, the less the air pollution. Emissions, chemical processing and meteorology determines the pollution levels. 2003 John Wiley and Sons Publishers
Smog in Los Angeles a) On a day with good ventilation of pollutants. b) On a day where pollutants (gases and particulate matter) are formed and trapped. Strong reduction In visibility and harmful levels of ozone (helat and crop damages)
Fokuserer nå på de svært høye episodiske konsentrasjonene av ozon om sommeren
OZONE POLLUTION IN THE UNITED STATES EPA standard: 84 ppbv 8-h avg not to be exceeded more than 3x/year 1980-1998 data Lin et al., JGR 2001
OZONE IMPACTS ON VEGETATION SUM06 Index: ozone dose in excess of 60 ppbv during growing season 1995 data Documented negative effects European Union has an AOT40 standard for ozone dose above 40 ppbv during growing season no such standard in the U.S.
Hydrokarboner identifisert i byluft i Barcelona (1991)
DEPENDENCE OF OZONE PRODUCTION ON NO x AND VOLATILE ORGANIC COMPOUNDS (VOCs) Take hydrocarbon RH as example of VOC O 3 HO x family O 3 P HOx RH OH 4 RO 2 NO 5 7 NO RO 6 O 2 HO 2 NO 2 9 8 HNO 3 O 3 H 2 O 2 High NOx OH + NO 2 Cycle broken P O3 : RH-limited Low NOx HO 2 + HO 2 Cycle broken P O3 : NOx-limited
DEPENDENCE OF OZONE PRODUCTION ON NO x AND VOLATILE ORGANIC COMPOUNDS (VOCs) Take hydrocarbon RH as example of VOC O 3 HO x family O 3 P HOx RH OH 4 RO 2 NO 5 7 NO RO 6 O 2 HO 2 NO 2 9 8 HNO 3 O 3 H 2 O 2 2 k4phox [ RH] P 1/ 2 PO ( P( O3) 2 k7 ( HOx 3) ) [ NO] k9[ NO2][ M] k8 NO x - saturated or NO x -limited regime hydrocarbon-limited regime
OZONE CONCENTRATIONS vs. NO x AND VOC EMISSIONS Air pollution model calculation for a typical urban airshed NO x -limited Ridge NO x - saturated
LATEST INVENTORIES OF BIOGENIC vs. ANTHROPOGENIC VOCs notice difference in scale! NB! Store naturlige utslipp av VOC fra løvskog. Noe mindre viktig i Europa Millet et al. [2007]
MAPPING OF VOC EMISSIONS FROM SPACE using satellite measurements of HCHO columns confirms dominance of biogenic over anthropogenic VOCs
EVEN IN NO x -LIMITED REGIME, THE TOTAL O 3 PRODUCED IS VOC-DEPENDENT AND [O 3 ] = f(e NOx ) IS STRONGLY NONLINEAR P(O 3 ) L(NO x ) HO 2,RO 2,O 3 OH, O 3 NO NO 2 HNO 3 hv Emission Deposition Define ozone production efficiency (OPE) as the total number of O 3 molecules produced per unit NO x emitted. Assuming NO x steady state, efficient HO x cycling, and loss of NO 2 by reaction with OH: OPE = P( O3) 2 k7[ HO2 ][ NO] 2 k4[ RH] L( NO ) k [ NO ][ OH ] k [ NO ] x 9 2 9 2 OPE m as NO x k e strong nonlinearity; in models, decreasing NO x emissions by 50% reduces ozone only by ~15%
1999-2004 NO x EMISSION REDUCTIONS AND SIMULATED EFFECTS ON SURFACE OZONE Hudman et al. [2007]
OBSERVED TREND IN OZONE BACKGROUND OVER CALIFORNIA IN SPRING SUGGESTS 10-15 ppbv INCREASE OVER PAST 20 YEARS Jaffe et al. [2003] Trend: 0.5-0.8 ppbv yr -1 Background: concentration that would be present in absence of local anthropogenic emissions
Observerte og beregnede endringer i ozon i troposfæren (fra utkast til IPCC, 2014)
RISING OZONE BACKGROUND IN EUROPE Changes in anthrop. NO x emissions Hohenpeissenberg/ Payerne polluted 3-5 km background Naja et al. [2003] Mace Head, 1987-2004 [Simmonds et al., 2004]
Europa Observerte trender i ozon om våren Stillehavsområdet
HEMISPHERIC OZONE POLLUTION: IMPLICATIONS OF ENHANCED OZONE BACKGROUND FOR MEETING AIR QUALITY STANDARDS (AQS) Europe AQS (8-h avg.) Europe AQS (seasonal) U.S. AQS (8-h avg.) U.S. AQS (1-h avg.) 0 20 40 60 80 100 120 ppbv Preindustrial ozone background Present-day ozone background at northern midlatitudes
PROJECTIONS OF GLOBAL NO x EMISSIONS Anthropogenic NO x emissions [IPCC, 2001] 2000 Optimistic IPCC scenario: OECD, U.S. m20%, Asia k 50% 2020 10 9 atoms N cm -2 s -1
EMEP/IPCC REPORT (Jan 05) The future ozone level in Europe is closely linked to global warming Methane (and CO) emission control is an effective way of simultaneously meeting air quality standards and abating global warming
EFFECT OF CLIMATE CHANGE ON OZONE AIR QUALITY Ozone exceedances of 90 ppbv, summer 2003 IPCC, 2007 Correlation of high ozone with temperature is driven by (1) stagnation, (2) biogenic hydrocarbon emissions, (3) reduced deposition, (4) chemistry
EKSTREMVERDIER AV OZON VED BAKKEN Beregnet bakkeozon under varmebølgen i August 2003 Verdiene høye nok til å gi betydelige helseeffekter Beregnet ekstra dødsfall som følge av høye ozonverdier: 15 20% Vil slike situasjoner vil opptre oftere i et fremtidig varmere klima?
Modellberegnet ozonøkning fra 2000 til 2100 som følge av økning I utslipp av forurensningsgasser Basert på økning i utslipp av forurensningsgasser kan lede til høye ozonverdier ved bakken Gi et betydelig bidrag til klimaøkning Store usikkerheter som følge av usikkerheter i fremtidige utslipp Begrenset ozonøkning er avhengig om en får til begrenset utslippsøkningen av primærgassene (CH 4, CO, NOx, VOC)
Utslipp av ozonforløpere i Norge http://www.ssb.no/agassn/
http://www.vegvesen.no/fag/publikasjoner/publikasjoner/statens+vegvesens+rapporter/_attachment/473517?_ts=13e9cbab590&fast_title=svv+rapport+173.pdf
Mer diesel Mer NOx og partikler Mindre CO og HC www.klif.no/publikasjoner/2438/ta2438.pdf Rapport fra 2008.