Chemical mechanisms and kinetics in atmospheric chemistry Lecture 8: Global budgets and emissions inventories

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1 Chemical mechanisms and kinetics in atmospheric chemistry Lecture 8: Global budgets and emissions inventories Mike Pilling University of Leeds UK Synopsis Global budgets for CH 4, CO, NO x, VOCs (tomorrow look at ozone). Projected emissions, IPCC 4AR Bottom-up inventories spatial, speciated, source apportioned. NO 2 recent changes in primary NO 2 emissions. Use of satellite retrievals + models to infer VOC emissions and evaluate inventories 1

2 Global budget for methane (Tg CH 4 yr -1 ) Sources: Natural 160 Anthropogenic 375 Total 535 Natural Sources: wetlands, termites, oceans Anthropogenic Sources: natural gas, coal mines, enteric fermentation, rice paddies, Sinks: Trop. oxidation 445 by OH Transfer to 40 stratosphere Uptake by soils 30 Total 515 Notes: 1. The rate of oxidation is k 5 [CH 4 ][OH], where the concentrations are averaged over the trop. 2. Concentrations of CH 4 have increased from 800 to 1700 ppb since pre-industrial times 3. Methane is a greenhouse gas. HISTORICAL TRENDS IN METHANE Historical methane trend Recent methane trend Northern hemisphere background CH4, µg m Baseline 12 month mean Recent measurements at Mace Head in W Ireland. 1μg m -3 = 0.65 ppb NB seasonal variation higher in winter Jan 2008 Jan 2007 Jan 2006 Jan 2005 Jan 2004 Jan 2003 Jan 2002 Jan 2001 Jan 2000 Jan 1999 Jan 1998 Jan 1997 Jan 1996 Jan

3 GLOBAL DISTRIBUTION OF METHANE NOAA/CMDL surface air measurements Seasonal dependence higher in winter than summer (maximum in NH correlates with minimum in SH). NH concentrations > SH main sources are in SH; slow transport across ITCZ. GLOBAL BUDGET OF CO 3

4 GLOBAL DISTRIBUTION OF CO NOAA/CMDL surface air measurements Compare CH 4. What are the differences and why? (Rate coefficients at 298 K/10-12 cm 3 molecule -1 s -1 : CH 4 : 7x10-3; CO: 0.24) Global VOC emissions (Tg yr -1 ) Anthropogenic: fuel production and distribution 17; fuel consumption 49; road transport 36; chemical industry 2; solvents 20; waste burning 8, other 10. Total 142 Tg yr -1 Biogenic: isoprene 503; monoterpenes 127; other reactive VOCs 260, unreactive VOCs 260; Total 1150 Tg yr -1 Typical atmospheric lifetimes (for [OH] = 1x10 6 molecule cm -3 ) τ = 1/k[OH] CH 4 6 yr isoprene 2.7 h CO 48 days ethane 46 days benzene 6 days ethene 30 h 4

5 Global budget for NOx Global sources (Tg N yr -1 ): Fossil fuel combustion 21; Biomass burning: 12 Soils 6 Lightning 3 Ammonia oxidation 3 Aircraft 0.5 Transport from strat 0.1 Coupling (rapid - ~ 1 minute in the day NO + O 3 NO 2 + O 2 NO 2 + Light NO + O; O + O 2 + M O 3 + M Also HO 2 + NO NO 2 + OH Loss OH + NO 2 + M HNO 3 + M Rainout of HNO 3 Lifetime of NO x is about 1 day. NO x is a key component in ozone formation. Can it be transported to regions where it is not strongly emitted? PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR LONG-RANGE TRANSPORT OF NO x 5

6 Projected emissions: Global NO x and CH 4 emissions to NO x CLE - current legislation SRES IPCC analyses MFR maximum feasible reduction Europe Asia + Oceania Africa + Middle East SRES A2 - World Total North America Latin America Maximum Feasible Reduction (MFR) SRES B2 - World Total CH SRES A2 :a very heterogeneous world based on self-reliance, regional differences in economic and technological development and continuous increase in global population Europe Asia + Oceania Africa + Middle East SRES A2 - World Total North America Latin America Maximum Feasible Reduction (MFR) SRES B2 - World Total Bottom-up spatially resolved continental emissions - VOCs Streets, D. G., et al. (2003a), An inventory of gaseous and primary aerosol emissions in Asia in the year 2000, J. Geophys. Res., 108(D21), 8809 Emissions are gridded at a variety of spatial resolutions from 1 1 to 30 s 30 s, using the exact locations of large point sources and surrogate GIS distributions of urban and rural population, road networks, landcover, ship lanes, etc. Biogenic emissions from Guenther et al. 6

7 Biogenic emissions inventories Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature). Guenther et al. Atmos. Chem. Phys., 6, , 2006 Includes dependence on temperature, light intensity, plant functiontype. Inventory includes mapping of plant function types in each grid square. 7

8 Global distribution of landscape-average isoprene emission factors (mg isoprene m 2 h 1 ). Spatial variability at the base resolution (1 km) is shown by regional images of the southeastern U.S. and southeastern Australia. (Emission factor represents the emission of a compound into the canopy at standard conditions) Global distribution of isoprene emission factors for the MEGAN PFTs 8

9 Monthly normalized isoprene emission rates estimated with MEGAN for Mapped National Emissions UK NAEI (National Atmospheric emissions Inventory) Spatial distribution of NOx emissions The NAEI is the standard reference for air emissions for the UK and provides annual estimates of emission for a wide range of important pollutants including air quality pollutants, greenhouse gases, regional pollutants leading to acid deposition and photochemical pollution, persistent organic pollutants and other toxic pollutants such as heavy metals. A spatial disaggregated 1x1 km inventory is produced each year. 9

10 NOx emissions UK 3000 NOx emission (ktonnes) Other Other transport & machinery Road transport Domestic Industry Public power NO 2 as an air pollutant. UK NOx emissions, Time dependence and source allocation Projections (AQEG, NO 2 in the UK, 2004) Recent road transport data for the UK 10

11 EU Air quality objectives limit values legally binding NO 2 1 hour mean 200 μg m -3 (105 ppb); (not to be exceeded >18 times per year) annual mean 40 μg m -3 (21 ppb) To be achieved by Possible to apply for derogation to 2015 Maps of annual mean background NO 2 concentrations UK 2001 UK 2010 Key AQ objective is annual mean of 40 μg m -3 to be achieved by 2010 (EU Directive) 11

12 Annual mean NO 2 concentrations, London London road links out of 1888 exceed 40 μg m -3 London road links out of 1888 exceed 40 μg m -3 Trends in roadside / kerbside NO and NO 2, UK 12

13 Estimates of ratio of NO 2 : NO x emissions, based on measurements of concentrations at Marylebone Rd, London Changes in emissions patterns primary NO 2 emissions from diesel vehicles 13

14 Use of satellite retrievals to evaluate emissions estimates MAPPING OF TROPOSPHERIC NO 2 FROM THE GOME SATELLITE INSTRUMENT (July 1996) Martin et al. [2002] 14

15 Quantifying emissions of natural VOCs using HCHO column observations from space GOME Biogenic Biomass Burning HCHO JULY 1996 (molec cm -2 ) Palmer et al. SEASONAL VARIABILITY IN GOME HCHO COLUMNS ( 97) over N America GOME GEOS-CHEM GOME GEOS-CHEM MAR JUL APR AUG MAY SEP JUN OCT molecules cm

16 HCHO columns July 1996 BIOGENIC ISOPRENE IS THE MAIN SOURCE OF HCHO IN U.S. IN SUMMER GOME footprint 320X40 km 2 GEIA isoprene emissions Palmer et al. JGR 111, D12315, 2006 [10 12 atoms C cm -2 s -1 ] GEOS-CHEM HCHO GOME HCHO [10 16 molec cm -2 ] Cumulative HCHO yield per C atom from isoprene oxidation. ([O 3 ] = 40 ppb, [CO] = 100 ppb, [isoprene] = 1ppb. CO, NO x, O 3 held constant.) Cummulative HCHO Yield from isoprene oxidation (per C) Vertical lines denote midnight of each day TIME (HOURS) NO X = 0.1 PPB NO X =1 PPB Full MCM mechanism. Final yield increased from GEOS-CHEM by 16% for high NOx, 65% low NOx 16

17 1000 [APINENE] PPT NOX = 1 PPB NOX = 100 PPT Decay of α pinene DAYS HCHO formation from α pinene acetone, which has a long atmospheric lifetime, is an intermediate in HCHO formation HCHO YIELD PER C REACTED DAYS NOX = 100 PPT NOX = 1 PPB [CH3COCH3] PPT CONCENTRATION OF CH3COCH3 FORMAED FROM 1PPB APINENE 900 CH3COCH3 NOX1PPB 800 CH3COCH3 NOX100PPT DAYS Relating HCHO Columns to VOC Emissions (Palmer) hours OH HCHO hours hν, OH VOC Ω HCHO Isoprene α-pinene 100 km VOC source propane Distance downwind Master Chemical Mechanism Ultimate Yield Y (per C) Approx. Time to Y isoprene ~ hrs α pinene ~ days β pinene ~ days MBO ~ days 17

18 Space-based formaldehyde measurements as constraints on volatile organic compound emissions in east and south Asia and implications for ozone (Fu et al., JGR, 112, D06312, doi: /2006jd007853, 2007) continuous 6-year record ( ) of GOME satellite measurements of formaldehyde (HCHO) columns over east and south Asia Limited to species with lifetimes and HCHO formation timescales < 1day (isoprene, alkenes, xylenes) Rescaled to full VOC emissions using speciation in inventory S E Asia VOC inventory and emissions inferred from GOME HCHO retrieval Fu et al., JGR, 112, D06312, doi: /2006jd007853,

19 Main conclusions from Fu study Wintertime GOME observations imply anthropogenic reactive NMVOC emissions from China, leading ~ 25% higher than Streets et al. (2003a). Attributed the difference to vehicular emissions. Biomass burning source for east and south Asia is almost 5 times the estimate of Streets et al. (2003a). GOME shows a large source from agricultural burning in the North China Plain in June missing from current inventories. Biogenic isoprene emission in east and south Asia derived from GOME is 56 ± 30 Tg yr1, similar to 52 Tg yr -1 from MEGAN. However, MEGAN underestimates emissions in China and overestimates emissions in the tropics GEOS-CHEM calculated differences in ozone formation: satellite inferred emission vs bottom-up inventories 19