Published on February 20, 2008
Slide1: TROPOSPHERIC CLEANSING/OXIDIZING CYCLES THE ATMOSPHERE: OXIDIZING MEDIUM IN GLOBAL BIOGEOCHEMICAL CYCLES: THE ATMOSPHERE: OXIDIZING MEDIUM IN GLOBAL BIOGEOCHEMICAL CYCLES EARTH SURFACE Emission Reduced gas Oxidized gas/ aerosol Oxidation Uptake Reduction Slide3: Primary source: O3 + hn g O2 + O(1D) (1) O(1D) + M g O + M (2) O(1D) + H2O g 2OH (3) THE OH RADICAL: MAIN TROPOSPHERIC OXIDANT TROPOSPHERIC OH PRODUCTION TAKES PLACEIN A NARROW UV WINDOW (290-320 nm): TROPOSPHERIC OH PRODUCTION TAKES PLACE IN A NARROW UV WINDOW (290-320 nm) 30o equinox midday Solar spectrum Slide6: OH + CO g H + CO2 H + O2 g HO2 (1) HO2 + NO g OH + NO2 CH4 + OH g CH3 + H2O CH3 + O2 g CH3O CH3O2 + NO g NO2 + CH3O (2) CH3O + O2 g CH2O + H2O CH2O + OH, hv g CO, OH, H2, HO2 TROPOSPHERIC HOx CYCLES THE OH RADICAL: MAIN TROPOSPHERIC OXIDANT THE OH RADICAL: MAIN TROPOSPHERIC OXIDANT: THE OH RADICAL: MAIN TROPOSPHERIC OXIDANT ATMOSPHERIC CLEANSING CO + OH g CO2 + H CH4 + OH g CH3 + H2O HCFC, VOC, Isop., … + OH NO2 + OH g HNO3 g H2O + … Major OH sinks GLOBAL MEAN [OH] = 1.0x106 molecules cm-3 Slide8: So what does all of this Tropospheric Oxidation have to do with Climate Change? Let’s check with an old friend. Slide9: IPCC AR4 SPM (2007) Warming Cooling TROPOSPHERIC OZONE PRODUCTION DEPENDS ON NOx, CO, CH4 AND OTHER ORGANIC COMPOUNDS : TROPOSPHERIC OZONE PRODUCTION DEPENDS ON NOx, CO, CH4 AND OTHER ORGANIC COMPOUNDS HOxfamily cycle OH RO2 RO HO2 HNO3 H2O2 O3 O3 O3 PHOx 4 5 6 7 8 9 RH NO O2 NO NO2 Take hydrocarbon RH Catalytic Tropospheric O3 Production NO + HO2/RO2 -> NO2 followed by NO2 + hv -> NO + O Slide11: SOURCES 3400-5700 Chemical production 3000-4600 HO2 + NO (70%) CH3O2 + NO (20%) RO2 + NO (10%) Transport from stratosphere 400-1100 [natural ozone] SINKS 3400-5700 Chemical loss 2900-4200 O(1D) + H2O (40%) HO2 + O3 (40%) OH + O3 (10%) others (10%) Dry deposition 500-1500 MASS 300 Present Day Budget Estimates For Tropospheric Ozone [tg O3] NOx EMISSIONS (Tg N yr-1) TO TROPOSPHERE: NOx EMISSIONS (Tg N yr-1) TO TROPOSPHERE FOSSIL FUEL 23.1 AIRCRAFT 0.5 BIOFUEL 2.2 BIOMASS BURNING 5.2 SOILS 5.1 LIGHTNING 5.8 STRATOSPHERE 0.2 MAPPING OF TROPOSPHERIC NO2FROM THE GOME SATELLITE INSTRUMENT (July 1996): MAPPING OF TROPOSPHERIC NO2 FROM THE GOME SATELLITE INSTRUMENT (July 1996) Martin et al.  LIGHTNING FLASHES SEEN FROM SPACE (2000): LIGHTNING FLASHES SEEN FROM SPACE (2000) DJF JJA NEAR FUTURE PROJECTIONS OF GLOBAL NOx EMISSIONS: NEAR FUTURE PROJECTIONS OF GLOBAL NOx EMISSIONS 109 atoms N cm-2 s-1 Anthropogenic NOx emissions [IPCC, 2001] 2000 2020 “Optimistic” IPCC scenario: OECD, U.S. m20%, Asia k 50% Slide16: IPPC’s “Optimistic” A1B View of the More Distant Future An Altenative View Grows to 75 TgN/yr by 2100 Impacts of O3 precursor reductions on global surface O3 : Impacts of O3 precursor reductions on global surface O3 Steady-state change in 8-hr daily maximum surface O3 averaged over 3-month “O3 season” from 20% reductions in global anthropogenic emissions NOx NMVOC CO CH4 West et al., submitted MOZART-2 model (2.8° x 2.8°) Slide18: West et al.,submitted Double dividend of methane controls: Improved air quality and reduced greenhouse warming AIR QUALITY: Change in population-weighted mean 8-hr daily max surface O3 in 3-month “O3 season” (ppbv) Steady-state results from MOZART-2 GLOBAL OZONE BACKGROUND:METHANE AND NOx ARE THE LIMITING PRECURSORS: GLOBAL OZONE BACKGROUND: METHANE AND NOx ARE THE LIMITING PRECURSORS GEOS-Chem model [Fiore et al., 2002] Ozone Climate forcing as sensitive to CH4 and NOx Sensitivity of global tropospheric ozone inventory (Tg) to 50% global reductions In anthropogenic precursor emissions Slide20: Tropospheric Ozone Issues: The Future Level is Uncertain Air Quality is focused on extreme values Climate forcing is driven by overall tropospheric column load Climate forcing is influenced at least as much by mid and upper tropospheric ozone Air Quality and Climate Change have the same general interest BUT… GLOBAL BUDGET OF METHANE: GLOBAL BUDGET OF METHANE Slide22: More than half of global methane emissions are influenced by human activities ~300 Tg CH4 yr-1 Anthropogenic [EDGAR 3.2 Fast-Track 2000; Olivier et al., 2005] ~200 Tg CH4 yr-1 Biogenic sources [Wang et al., 2004] ANIMALS 90 LANDFILLS + WASTEWATER 50 GAS + OIL 60 COAL 30 RICE 40 TERMITES 20 WETLANDS 180 BIOMASS BURNING + BIOFUEL 30 GLOBAL METHANE SOURCES (Tg CH4 yr-1) Estimates for Changing Methane Sources in the 1990s: Estimates for Changing Methane Sources in the 1990s 547 Tg CH4 yr-1 EDGAR anthropogenic inventory Biogenic adjusted to maintain constant total source BASE GLOBAL DISTRIBUTION OF METHANENOAA/CMDL surface air measurements : GLOBAL DISTRIBUTION OF METHANE NOAA/CMDL surface air measurements HISTORICAL TRENDS IN METHANE: HISTORICAL TRENDS IN METHANE Historical methane trend Recent methane trend RECENT TREND IN METHANE: RECENT TREND IN METHANE Observed trend in surface CH4 (ppb) 1990-2004: Observed trend in surface CH4 (ppb) 1990-2004 Data from 42 GMD stations with 8-yr minimum record is area-weighted, after averaging in bands 60-90N, 30-60N, 0-30N, 0-30S, 30-90S NOAA GMD Network Global Mean CH4 (ppb) Hypotheses for leveling off discussed in the literature: 1. Approach to steady-state 2. Source Changes Anthropogenic Wetlands/plants (Biomass burning) 3. (Transport) 4. Sink (CH4+OH) Humidity Temperature OH precursor emissions overhead O3 columns Can the model capture the observed trend (and be used for attribution)? A “WIN-WIN” CASE: Methane emission controls improve air quality and climate: A “WIN-WIN” CASE: Methane emission controls improve air quality and climate West & Fiore, 2005; West et al., 2006 Proposed EPA rule costs ~$1 billion yr-1 to reduce U.S. ozone by 1 ppb Cost-effective reductions avoid 370,000 global premature mortalities over 20 years; decrease climate forcing; avoid other damages to health, agriculture, forests, valued at $5 billion Decrease in global anthropogenic methane emissions Cost-saving reductions Cost-effective reductions (<$10/ton CO2 eq.) All identified reductions 0.5 ppbv 1.0 ppbv 1.5 ppbv Decrease in global ozone smog Slide29: West et al.,submitted Double dividend of methane controls: Improved air quality and reduced greenhouse warming AIR QUALITY: Change in population-weighted mean 8-hr daily max surface O3 in 3-month “O3 season” (ppbv) Steady-state results from MOZART-2 CLASSIC GENERAL EXAM QUESTIONS: CLASSIC GENERAL EXAM QUESTIONS 1. Loss of NOx in the troposphere takes place by NO2+OH, same as in the stratosphere. What is the effect of this reaction on tropospheric ozone. 2. Another version of that question. Why does NOx destroy stratospheric ozone and produce tropospheric ozone? 3. How might global warming affect the source of OH in the troposphere? 4. What would be the feedbacks on global warming [+ or -]?