Seminar slides for AGU2005May yueli

Potential Effects of CH4 and N2O on the Recovery of Stratospheric Ozone : 

Potential Effects of CH4 and N2O on the Recovery of Stratospheric Ozone Yue Li Department of Atmospheric Sciences University of Illinois, Urbana, IL March 3 , 2005

Purpose of the study : 

Purpose of the study Further understanding of trace gas effects on ozone and climate Examine the possible range of effects of human activities on the recovery of stratospheric ozone Provide scientific information for policy consideration

Brief introduction to UIUC 2D CTM: 

Brief introduction to UIUC 2D CTM  First developed at Lawrence Livermore National Laborotory by Don Wuebbles and colleagues  Zonally-averaged global model of atmospheric chemistry and physics  78 species of gases, altitude 84km, 1.5km(height)×5º(latitude) grid box  161 thermal reactions, 56 photolytic reactions  Transport of chemical species: advection, turbulent eddy transport, convection Transport updated to compare well with age of air analyses for stratosphere

UIUC Zonally-Averaged Chemical-Transport Model: 

Anthropogenic Emissions All Halocarbons surface concentrations or emissions based on WMO (2002) scenario “Ab” updated using NOAA CMDL observations. Solar Radiation Irradiance in wavelength of 175.4 – 735.0 nm from 1970 to 2002 based on solar data from Judith Lean and colleagues. Stratospheric Sulfate Aerosols Based on evaluation of SAGE and SAGE II aerosol measurements for 1980 to 2002 by Larry Thomason and colleagues. Climate Change (Temperature) Annual temperature data. From NCEP Reanalysis Data (1000mb –10mb) and CPC Data (10mb- 0.5mb) UIUC Zonally-Averaged Chemical-Transport Model

Current stage of study on ozone change: 

Current stage of study on ozone change With the execution of Montreal Protocol, stratospheric ozone should recover gradually as a result of the control on CFCs New problems from non-controlled chemicals, i.e., increasing trace gases like CH4, NO2 Basis for the new study Other human activities could also impact ozone, i.e. effects on climate Examine projections of human effects on future ozone and on ozone recovery

Will the ozone really recover?: 

Will the ozone really recover? A lessening of the ozone decline, followed by an increase in total ozone “Recovery” (by definition) is considered to have occurred when total ozone returned to 1979 levels In addition to total ozone, look for increase in ozone with latitude and altitude

Potential effects of trace gases on ozone recovery: 

Potential effects of trace gases on ozone recovery Not well understood, but could be significant. Chemistry processes play an important role in the ozone change Early study focused on mechanisms involving radiative transfer and temperature change, most in Northern Hemisphere Two major trace gases (also greenhouse gases), Methane and Nitrous Oxide, are the most interesting

Atmospheric Methane: 

Atmospheric Methane From Agriculture and Fossil fuel and Biomass burning Major long lived GHG. Sink of Cl and OH CH4+OHCH3+H2O(88%) CH4soil(5%) CH4stratosphere(7%) Source: NOAA CMDL

Slide9: 

Nitrous Oxide (N2O) From Agriculture and Nitrogen fertilizers(large uncertainty) Long lived GHG, well mixed Inertia in troposphere Major sources of statospheric Nox N2O+O(1D)  2NO(58%) N2O+O(1D)  N2+O2(42%)

IPCC Scenarios for CH4 and N2O: 

IPCC Scenarios for CH4 and N2O A1 family: a rapidly developing future world, alternative developments of energy A1B: a balance across all sources A1T: non-fossil energy sources A1F1: fossil intensive A2 family: a very heterogeneous world, self- reliance and preservation of local identities B1 family: a convergent world, population peak as A1, global solutions to development B2 family: emphasis on local solutions to economic, social & environmental sustainability

Ozone Recovery for Different Scenarios: 

Ozone Recovery for Different Scenarios A1T Fastest B1 Slowest Difference by 2050: 1.3 % Global

Analysis strategy: 

Analysis strategy Select comparison pairs, i.e., A1T (fastest,more CH4) and B1(slowest, more N2O) Evaluate chemical processes involving N2O and CH4 Analyses with either CH4 or N2O scenarios

Partitioning of catalytic cycles of ozone depletion: 

Partitioning of catalytic cycles of ozone depletion NOx dominates middle stratosphere, while HOx dominates below Halogen cycles are sensitive to altitudes, with two peaks in the upper and lower stratosphere HOx and NOx cycles contribute most in summer when UV level is high Figure. The ozone loss rate resulting from catalytic cycles involving NOx, HOx, Halogen and Ox families as a function of annual average total ozone loss rate for 30N in 2003 computed by the UIUC 2D CTM

Ozone Distribution Never Really Recovers: 

Ozone Distribution Never Really Recovers A1T B1 Absolute ozone change relative to 1980 No recovery really happens

Seasonal change of total ozone distribution: 

Seasonal change of total ozone distribution Roughly independent on season along the equator and for mid latitudes, except for polar regions NOx becomes more important from lower latitudes to higher latitudes Increasing CH4 contributes most in the most populated area

Sensitivity study of B1 and B2 scenario: 

Sensitivity study of B1 and B2 scenario Constant CH4 Constant N2O B1 B2 Figure. Changes in percent unit annual average column ozone relative to 1980 conditions for B1 and B2) scenario in 2050

2003-2100 Long Term Ozone Recovery: 

2003-2100 Long Term Ozone Recovery 50 S – 50 N

2003-2100 Long Term Ozone Recovery: 

2003-2100 Long Term Ozone Recovery 50-90 S

2003-2100 Long Term Ozone Recovery: 

2003-2100 Long Term Ozone Recovery 50-90 N

Conclusions: 

Conclusions Detection of significant increases in total ozone may take several decades (20-40 years) Total ozone will likely increase through 2050, but will it have “recovered”? Future growth in CH4 and N2O will play major roles in determining the “recovery” of ozone, and whether it will recover For some scenarios, ozone never recovers and there is destruction in ozone occurs after 2050 (depends on relative N2O and CH4 increase Climate changes (T, dynamics, H2O) also likely to affect recovery Large latitudinal differences in the rate of recovery Even when considered to be recovered the distribution of ozone will be different than it was in 1980.

Slide21: 

Thank you & Questions