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methane control reduction emissions concentration
- 1. Hg Hg Environmental mercury and the role of the atmosphere
- 2. Mercury from fish consumption: a global environmental issue Children IQ deficits (fetal exposure) Well-established $8 billion per year cost in US Adult cardiovascular, fertility effects Suspected EPA reference dose (RfD): 0.1 μg kg-1 d-1 (about 2 fish meals per week) Hg (mg/kg) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Tilefish Shark Swordfish Orange Roughy Marlin Tuna-fresh Tuna-canned alb Bluefish Grouper, Rockfish Scorpionfish Halibut Sea trout Sablefish Snapper Lobster Mackerel Skate Tuna-canned lght Cod Croaker Squid Whitefish Pollock Crab Tilefish Shark Swordfish Orange Roughy Marlin Canned Tuna (alb) Bluefish Grouper, Rockfish Scorpionfish Halibut Sea trout Sablefish Lobster Snapper Lobster Mackerel Skate Canned Tuna (lt) Cod Croaker Squid Whitefish Pollock Crab Mercury biomagnification factor Salmon
- 3. Electronic structure of mercury Mass number = 80: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 • Filling of subshells makes elemental Hg(0) stable, liquid, volatile • Mercury can also shed its two outer electrons (6s2) to produce Hg(II) (mercuric) compounds 6s2 oxidation Hg(0) Hg(II) reduction elemental mercury mercuric compounds
- 4. Biogeochemical cycle of mercury Hg(0) Hg(II) particulate Hg burial SEDIMENTS uplift volcanoes erosion oxidation Hg(0) Hg(II) reduction biological uptake ANTHROPOGENIC PERTURBATION: fuel combustion Mining ~10x natural ATMOSPHERE OCEAN/SOIL VOLATILE WATER-SOLUBLE
- 5. Atmosphere enables global transport of mercury Observed variability of atmospheric Hg implies an atmospheric lifetime against deposition of about 0.5 years Implies gPresent-day cale transport of anthropogenic emissions Present-day emission of mercury to atmosphere from coal and mining Atmospheric concentrations UNEP [2013]; Horowitz et al. [2017]
- 6. Mercury wet deposition is controlled by global transport EPA deposition data (circles), model (background) Global Hg(II) pool scavenging Florida T-storm Highest mercury deposition in US is along the Gulf Coast, where thunderstorms scavenge globally transported mercury from high altitudes Selin and Jacob [2008]
- 7. Atmospheric redox chemistry of mercury: driver of mercury deposition • Oxidation of Hg(0) by OH is too slow • Oxidation by Br atoms is currently thought to dominate 2 2 Hg+Br+M HgBr+M HgBr+X+M HgBrX+M X OH, Br, Cl, NO , HO HgBrX+ Hg+Br+X hv ocean plankton CHBr3 bromoform OH weeks deposition Br HBr Hg(0) Hg(II) hv deposition Still very uncertain!
- 8. New York Times, 4/24/2021 “Methane gets less attention than its big bad brother, carbon dioxide, but in truth methane is like carbon dioxide on steroids,” Senator Chuck Schumer, the majority leader, said on Thursday.
- 9. Radiative forcing of climate referenced to emissions, 1750-2011 • Methane is 60% as important as CO2 in explaining past warming • Atmospheric lifetime of methane is 9 years, much shorter than CO2 (> 100 years) Methane is most relevant as a near-term (~20 years) climate forcer Methane and CO2 emissions should not be “equivalent” in climate policy [IPCC, 2014] Methane: 2nd anthropogenic greenhouse gas after CO2
- 10. Why does methane cause only a short-term temperature response? To To To + To To Fin t < 0 t = 0 t = 20 years t = 100 years climate equilibrium methane emission pulse Earth has warmed but methane is gone back to original equilibrium Fout F = 0 F = 0 F < 0 F > 0 Earth starts warming Earth starts cooling back warming is gone
- 11. How to quantify the importance of methane versus CO2? Climate policy metrics consider the integrated impact of a pulse unit emission of a radiative forcing agent Inject 1 kg of agent X at time t = 0 time Concentration C(t) from pulse time Impact from pulse = f(C(t)) time time Discount rate Climate metric = 0 (impact)(discount rate)dt …usually normalized to CO2
- 12. Standard IPCC metric: Global Warming Potential (GWP) Integrated radiative forcing over time horizon [0, H] CO2 methane Radiative forcing F vs. time for pulse unit emission of X at t = 0 GWP for methane vs. chosen time horizon: 28 for H = 100 years 1 Tg CH4 = 28 Tg CO2 (eq) IPCC [2014] GWP is easy to compute, but it does not correspond to any physical impact 0 ( ) H X F t dt 2 AGWP(X) Δ AGWP(X) GWP(X) AGWP(CO ) H Discount rate: step function
- 13. Global temperature potential (GTP) as alternative policy metric Global mean surface temperature change at t = H CO2 methane Temperature change vs. time for pulse unit emission at t = 0 Temperature response to actual 2008 emissions taken as a 1-year pulse IPCC [2014] Methane as important as CO2 for 10-year horizon, unimportant for 100-year horizon , , 2 ( ) ( ) ( ) o X o CO T H GTP X T H Δ Δ Discount rate: Dirac function H
- 14. Controlling methane should be part of climate policy … but for reasons totally different than CO2 • It addresses climate change on time scales of 10-20 years – which we care about • It offers decadal-scale results for accountability of climate policy • It is an alternative to geoengineering by aerosols • It is relatively easy – you can go a long way by fixing leaks, harvesting gas • It has important air quality co-benefits and can make money • Measures to reduce emissions can have lasting effects over long time horizons
- 15. Methane is a major greenhouse gas… but where does it come from? Complexity of methane sources Wetlands Livestock Oil/gas Waste Satellite observations hold the key! Wetlands: 161 Fires: 15 Livestock: 117 Rice: 38 Oil/Gas: 70 Coal: 38 Waste: 68 Other: 42 CH4 Lifetime 9.4±0.9 years Emission 549 60 Tg a-1 CO2 Rice Tropospheric OH: 89% Maasakkers et al. [2019] Global bottom-up inventories: Emission = Activity x Emission factor
- 16. Methane has increased in fits and starts over past 40 years Methane CO2 CO2 Renewed rise since 2006 has been attributed to oil/gas, livestock, rice, wetlands, OH… bottom line is that we don’t know why methane is rising
- 17. The latest drama: methane surged in 2020 – why?
- 18. Using satellite observations to monitor methane emissions 3-D chemical transport model relates emissions to concentrations predicted concentrations observed atmospheric concentrations compare correct bottom-up inventory inversion
- 19. GOSAT methane observations (2009-present) Maasakkers et al. [2019] 2010-2015 mean methane 1.2 million observations
- 20. Attribution of 2010-2018 methane trends using GOSAT • Most of the trend is attributed to tropical livestock and rice • 2014 surge attributed to OH Zhang et al. [2021]
- 21. TROPOMI methane observations (May 2018 – present) • Global daily coverage at 7x7 km2 pixel resolution • 4% retrieval success limited by clouds, surface heterogeneity, aerosols Daniel Varon, Harvard Sep 2018 – Aug 2019 mean methane
- 22. Permian Basin: fast increase in oil/gas production, now accounts for over 10% of US methane emission TROPOMI observations of US methane
- 23. Observing large methane point sources with land-imaging spectrometers Landsat: 100 nm spectral resolution, useless for methane LandSat over Boston AVIRIS-NG over Permian: methane plumes Oil well plume in Algeria, observed by Sentinel-2 for almost a year Cusworth et al. [2021], Varon et al. [2021]