Overview of Global Warming, Ozone Depletion, and Air Quality

Transcription

1 Overview of Global Warming, Ozone Depletion, and Air Quality AOSC 433/633 & CHEM 433/633 Ross Salawitch Class Web Site: Notes: Ross, Allison & Tim co-teach this class; please include all of us on class related unless you are writing to set up a meeting with one of us Lectures are the glue that hold this class together: therefore, attendance is strongly encouraged We like to ask questions for many reasons: to get to know you, to keep you engaged, etc. Please participate at your own level of comfort Problem sets tend to be quantitative and exams tend to be qualitative: Problem Set #1, due 2 weeks from today, has been posted We encourage students to start working on Problem Set #1 soon and not wait until the night before due date to get started Lecture 2 29 January Overview of Global Warming, Ozone Depletion, and Air Quality Course theme: effect of human activity on atmospheric composition climate change air quality stratospheric ozone depletion and recovery Today s goals: 1) Overview of climate change, air quality, and ozone depletion 2) We ll provide lots of detail today we do not expect all of these details to stick. We do expect, however, that when you review this lecture at the end of semester, details will be understandable 3) Linkages between these topics, which are often thought of as disparate, but actually are linked in profoundly important manners Please complete the Learning Outcome exercise following lecture to review salient take away messages from today 2

2 Motivational Words: 21 Jan 2013 We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations. Some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires and crippling drought and more powerful storms. The path towards sustainable energy sources will be long and sometimes difficult. But America cannot resist this transition, we must lead it. We cannot cede to other nations the technology that will power new jobs and new industries, we must claim its promise. That s how we will maintain our economic vitality and our national treasure our forests and waterways, our crop lands and snow capped peaks. That is how we will preserve our planet, commanded to our care by God. That s what will lend meaning to the creed our fathers once declared. Text: Image: 3 Greenhouse Effect Question 1.3, IPCC,

3 Radiative Forcing of Climate, 1750 to 2005 Question 2.1, IPCC, Radiative Forcing Question 1.1, IPCC, 2007 Radiative Forcing of Climate is Change in Energy reaching the lower atmosphere (surface to tropopause) as GHGs rise. Back Radiation is most important term. 6

4 Modern CO 2 Record Legacy of Charles Keeling, Scripps Institution of Oceanography, La Jolla, CA 7 GHG Record Over Last Several Millennia Question 2.1, IPCC,

5 GWP (CH ) = time final time initial 4 time final time initial GWP Global Warming Potential a a [CH (t)] dt CH4 4 [CO (t) dt] CO2 2 where: a CH4 = Radiative Efficiency (W m 2 kg 1 ) due to an increase in CH 4 a CO2 = Radiative Efficiency (W m 2 kg 1 ) due to an increase in CO 2 CH 4 (t) = time-dependent response to an instantaneous release of a pulse of CH 4 CO 2 (t) = time-dependent response to an instantaneous release of a pulse of CO 2 9 GWP Global Warming Potential from IPCC 2007 Physical Science Basis 10

6 GWP Global Warming Potential Over the time horizon of ~1750 to 2005: RF CH 4 relative to CO ppb / 100 ppm = = 0.33 RF N 2 O relative to CO ppb / 100 ppm = = 0.11 Total RF CH 4 + N 2 O relative to CO This rough estimate is not too different than the RF of CH 4 + N 2 O relative to RF of CO 2, ~38%, from FAQ 2.1, Figure 2 11 Solar and Volcanic Forcings (Model Inputs) IPCC 2001 Climate Change: Scientific Basis 12

7 GHGs, Aerosols, & O 3 Forcings (Model Inputs) IPCC 2001 Climate Change: Scientific Basis 13 All Forcings (Model Inputs) IPCC 2001 Climate Change: Scientific Basis 14

8 Modeling Climate Change Modeling Climate Change Are humans responsible? Orbital variations: too slow Volcanoes: no sustained forcing Solar variability: Perhaps dominant forcing of Medieval Warming and Little Ice Age Small effect since ~1860 Recent Data Historic Data Modern Max Medieval Max Maunder Min Reconstructed Temperature YEAR YEAR 15 Are humans responsible? Orbital variations: too slow Volcanoes: no sustained forcing Solar variability: Perhaps dominant forcing of Medieval Warming and Little Ice Age Small effect since ~1860 Internal variability (eg, El Niño / La Niña) : Climate record from 1000 to 1850 shows nothing like sustained, present rate of warming Year

9 Modeling Climate Change Are humans responsible? Orbital variations: too slow Volcanoes: no sustained forcing Solar variability: Perhaps dominant forcing of Medieval Warming and Little Ice Age Small effect since ~1860 Internal variability (eg, El Niño / La Niña) : Climate record from 1000 to 1850 shows nothing like sustained, present rate of warming IPCC Climate Change 2007: The Physical Science Basis concludes: Very high confidence* the globally averaged net effect of human activities since 1750 has been one of warming * At least a 9 out of 10 chance of being correct IPCC Intergovernmental Panel on Climate Change Note: IPCC models do not include climate-carbon cycle feedback nor do they include ice sheet dynamics 17 Earth s Atmosphere Effect of Humans Stratospheric Ozone shields surface from solar UV radiation Update After Farman et al., Large losses of total ozone in Antarctica reveal Seasonal ClOx/NOx interaction, Nature, 315, 207, Rising chlorine due to industrial activity 18

10 Ozone Depletion and Halocarbons ODP (species " i") = global loss of O 3 due to unit mass emission of " i" global loss of O 3 due to unit mass emission of CFC-11 τ i MWCFC-11 1 ( α nbr + ncl ) τ MW 3 CFC-11 where : τ is the global atmospheric lifetime MW is the molecular weight i n is the number of chlorine or bromine atoms is the effectiveness of ozone loss by bromine α relative to ozone loss by chlorine 19 CFC Usage Prior to the Montreal Protocol The uses of CFCs in various sectors before the 1987 Montreal Protocol, which required countries to phase out their production to protect the ozone layer. From: 20

11 What is this compound? F Cl C F Cl How is it eventually removed from the atmosphere? What does it produce upon its removal? 21 When CFCs Decompose (in the stratosphere) They Produce Chlorine Radicals Radicals Odd number of electrons - unpaired electron in outer valence shell Go to great lengths to pair off lone electron Exceptionally reactive Cl Cl O O ClO : Chlorine monoxide See pages 57 to 68, Ch 2, Chemistry in Context, for description of Lewis Dot Structures of atmospherically important species 22

12 Chlorine Radicals Lead to Ozone Loss ClO + ClO + M ClOOCl + M Cl + O 3 ClO + O 2 Cl + O 3 ClO + O 2 ClOOCl + hν ClOO + Cl ClOO + heat Cl + O 2 23 Montreal Protocol Has Banned Most Industrial Production of CFCs and Halons Jan 2013 Lecture Chlorine content, all long-lived halocarbons CH 3 Cl from natural sources Rising chlorine due to industrial activity and the ozone layer is perhaps in initial phase of recovery 24

13 Link Between Ozone-Depleting Substances (ODS) and Climate Change Most ozone depleting substances have a significant GWP Twenty Questions and Answers About The Ozone Layer: 2010 Update (WMO, 2010) GWP weighted emissions of CO 2 GWP weighted emissions of CFCs, without early aerosol propellant ban (i.e., no ban on CFCs) ODS Actual GWP weighted emissions of CFCs, without Montreal Protocol Velders et al., PNAS, Tropospheric Ozone Production OH + CO CO 2 + H H + O 2 +M HO 2 + M HO 2 + NO OH + NO 2 NO 2 + hν NO + O O + O 2 + M O 3 + M NO & NO 2 : Emitted by fossil fuel combustion & biomass burning High T N 2 + O 2 2 NO CO: Emitted by fossil fuel combustion & biomass burning Complete combustion: 2 C 8 H O 2 16 CO H 2 O Extreme, incomplete combustion: 2 C 8 H O 2 16 CO + 18 H 2 O 26

14 Tropospheric Pollutants (The Air We Breathe) Criteria Pollutants From Chapter 1 Chemistry in Context Criteria pollutant: identified as being common-place and detrimental to human welfare (i.e., ubiquitous pollutant) 27 Significant Improvements in Air Quality since early 1980s Chapter 1 Chemistry in Context 28

15 Significant Improvements in Local Air Quality since early 1980s earchcenter/publications/general/emde/vol4no8/article4_photo1.aspx 29 Significant Improvements in Local Air Quality since early 1980s Pages/HistoricalData.aspx 30

16 Air Quality Standards and Why We Care Year Averaging Period EPA Surface Ozone Standard hr 125 ppb hr 85 ppb hr * 75 ppb 2013 #?????? * The 8 hr standard is met when the 3-yr average of the annual 4 th highest daily maximum 8 hr O 3 is less than 75 ppb. Increased risk of premature mortality for even low levels of surface O 3 ; further reductions will benefit public health Bell et al., # On 2 Sept 2011, President Obama directed EPA to postpone revising the surface O 3 standard until 2013, so that regulatory burdens would not interfere with economic recovery: 31 Reading: Next Lecture: Fundamentals of Earth s Atmosphere (Tim) Chemistry in Context, Sections 1.1, 1.2, and 1.5 Jacobson: pages 50 to 64 Admission Ticket for Lecture 3 is now posted at: Please bring a calculator to class on Thursday 32