overview of the arctic middle atmospheric chemistry theme

Overview of the Arctic Middle Atmospheric Chemistry

Theme

Kimberly Strong

Department of Physics, University of Toronto

Co-Investigators: J. Drummond, H. Fast, A. Manson, T. McElroy, G. Shepherd, R. Sica, J. Sloan, K. Strawbridge, K. Walker, W. Ward, J. Whiteway

Collaborators: J. McConnell, P. Bernath, T. Shepherd

Students: C. Adams, A. Fraser, D. Fu, F. Kolonjari, R. Lindenmaier, H. Popova

Post-docs: R. Batchelor, T. Kerzenmacher, K. Sung, M. Wolff

Env. Canada: M. Harwood, R. Mittermeier

CANDAC: P. Fogal, A. Harrett, A. Khmel, C. Midwinter, P. Loewen, O. Mikhailov, M. Okraszewski (Thanks to all!)

CANDAC Workshop #5Toronto, 24-26 October 2007

Overview

Polar Stratospheric Ozone Trends

The Need for Arctic Measurements

The Arctic Middle Atmosphere Chemistry Theme

The First Year of AMAC Activities

Outlook

Introduction

Arctic middle atmosphere chemistry Focus here is on the stratosphere and the ozone budget Coupled to troposphere & mesosphere, dynamics & radiation

Stratospheric ozone Highly effective absorber of harmful UV-B solar radiation Dominant source of radiative heating in the stratosphere This heating determines the stratospheric temperature

distribution, which, in turn, influences stratospheric winds

Consequences of a decrease in Arctic stratospheric ozone Enhancement of UV-dependent photochemical reactions in the

troposphere Decrease in radiative forcing Reduction in stratospheric temperatures Change in stratospheric dynamics

Polar Total Ozone Trends

WMO Ozone Assessment 2006

Seasonal Total Ozone Trends

Total ozone column trends as a function of equivalent latitude

and season using TOMS and GOME data for 1978-2000

x - mean position of vortex edge

Eq. Latitude - a potential vorticity coordinate with vortex centre at 90°

Largest Arctic trend is 1.04 ± 0.39 % per year in March

WMO Ozone Assessment

2002

Arctic Ozone: March Averages


2006

March monthly averaged total ozone from satellites

•Nimbus-4 BUV•Nimbus-7 TOMS•NOAA-9 SBUV/2•Earth Probe TOMS•Aura OMI

Latitudinal Total Ozone Trends

Measured and modelled latitudinal total ozone trends


2006

Polar Ozone Depletion - Processes

(1) Formation of the winter polar vortex (band of westerly winds) isolates cold dark air over the polar regions

(2) Low temperatures in the vortex, T<195 K PSCs form in the lower stratosphere (liquid & solid HNO3,H2O,H2SO4)

(3) Dehydration and denitrification remove H2O & nitrogen oxides which could neutralize chlorine

(4) Release of CFCs, mixing, and transport to the polar regions enhanced levels of chlorine and other halogen species

(5) Heterogeneous reactions on the PSCs convert inactive chlorine (HCl and ClONO2) into reactive Cl2

(6) Sunlight returns in the spring UV radiation breaks Cl2 apart to form Cl

(7) Catalytic chlorine and bromine cycles destroy ozone, while recycling Cl

This continues until the Sun causes a dynamical breakdown of the winter vortex and PSCs evaporate.

Frieler at al., 2006; WMO Ozone Assessment 2006

= BrO + BrCl

The Role of Bromine Significant source of uncertainty May be more important

(by 10-15%) in polar ozone depletion than previously thought

BrO + ClO cycle estimated to contribute up to 50% of chemical loss of polar ozone

Bry may be 3-8 ppt larger than expected from CH3Br + halons source due short-lived

bromocarbons and tropospheric BrO ?

Arctic Vortex and Ozone LossLarge variation from year to year in

area of the Arctic vortex (dominates circulation from Nov. to March) strength of the sudden warmings associated with planetary-scale waves

originating in the troposphere timing of the final vortex breakdown

Large variability in Arctic ozone (short & long term) is due to: variability in transport of air in the stratosphere variability in tropospheric forcing variations in chemical ozone loss

Chemical consequences of variability in vortex meteorology: area over which T is below threshold for PSC formation amount of sunlight available to drive chemical ozone loss and the volume of

air processed through cold regions timing of the cold periods the location of the cold areas within the vortex position of the vortex when cold areas develop

Chemical reaction rates

Stratospheric circulation

Stratospheric ozone

Stratospheric temperature UV

Processes Affecting Stratospheric Ozone and Temperature

Brasseur, SPARC Lecture 2004, after Schnadt et al., Climate Dynamics 2002



Stratospheric ozone


Vertical propagation of planetary and gravity waves





Anthropogenic emissions of CO2, CFCs, CH4, N2O

Greenhouse gases

Stratospheric ozone









Greenhouse gases

Stratospheric ozone


Troposphere-stratosphere exchange


Stratospheric chlorine, bromine, and nitrogen

oxides





PSC formation


Greenhouse gases

Stratospheric ozone

Stratospheric temperature

CH4 oxidation

Stratospheric water vapour

UV

Troposphere-stratosphere exchange


Stratospheric chlorine, bromine, and nitrogen

oxides


Future Impact of Climate Change

Will climate change enhance or reduce polar ozone loss?Two possibilities: The stratospheric vortex becomes stronger and colder, and

there is a positive Arctic Oscillation trend (e.g., Shindell et al., 1999). increasing CO2 cools the stratosphere, strengthens the polar vortex

such cooling could increase formation of PSCs results in more Arctic ozone loss observations suggest 15 DU Arctic ozone loss per Kelvin cooling

“Dynamical heating” causes a more disturbed and warmer NH stratospheric vortex (e.g., Schnadt et al., Clim. Dyn. 2002; Schnadt & Dameris, GRL 2003). enhancement of planetary wave activity causes a weaker and warmer polar vortex results in less Arctic ozone loss - faster recovery

Two Possibilities

(1) Cooling of stratosphere:T (K) (July) in response to CO2 doubling from the Hammonia Model(Brasseur, SPARC Lecture 2004)

(2) Warming of stratosphere:T (K) (DJF) from 1990 to 2015 from the ECHAM model (Schnadt et al., Clim. Dyn. 2002)

Sensitivity of Arctic Ozone Loss to TO

zone

col

umn

loss

[ D

U ]

(14-

25 k

m,

mid

-Jan

to

late

Mar

ch)

Rex et al., GRL 2004, 2006; WMO Ozone Assessment 2006

squares, red line - ozonesondes

circles, green line - HALOE

B&W circles, black lines - SLIMCAT

Overall cooling trend in the global-mean lower stratosphere is ~0.5 K/decade (1979-2005)~ 15 DU additional chemical ozone loss

per Kelvin cooling of the Arctic stratosphere

~5-6 K temperature change

~80 DUozone loss

Ozo

ne c

olum

n lo

ss [

DU

](~

14-2

5 km

, m

id-J

an t

o la

te M

arch

)

An Example - Winter 2005

The Arctic vortex was unusually cold and stable in early winter 2005...

Courtesy of C.T. McElroy and J. Davies, EC

1985 - Vienna Convention for the Protection of the Ozone Layer

1987 - Montreal Protocol on Substances that Deplete the Ozone Layer Entered into force in 1989 Established controls on halogen

source gases Later strengthened by a series of

Amendments

Montreal Protocol



2006

Recovery of Stratospheric Ozone

IPCC/TEAP SROC 2005

Changes in total ozone from 60°S to 60°N

Polar Ozone - Predictions

Gradual recovery of ozone is anticipated as stratospheric chlorine decreases ozone turnaround in the Arctic

likely before 2020

vunerable to perturbations, such as aerosols from volcanoes

coupled to stratospheric cooling

extreme Arctic ozone loss is not predicted


Spring Polar Ozone Anomalies


“… the frequency of measurements deep in the Arctic vortex remains low. The situation is unsatisfactory given the highly non-linear sensitivity of Arctic stratospheric ozone to cold winters. … Chemical and dynamical perturbations caused by strong volcanic eruptions make it impossible to derive a linear trend [in total ozone], which highlights the importance of continuous measurements throughout the expected recovery of the ozone layer during the coming decades.”

IGOS 2004 Atmospheric Chemistry Report


“With regard to the Arctic, the future evolution of ozone is potentially sensitive to climate change and to natural variability, and will not necessarily follow strictly the chlorine loading. There is uncertainty in even the sign of the dynamical feedback to WMGHG changes. … Progress will result from further development of CCMs [chemistry-climate models] and from comparisons of results between models and with observations.”

IPCC/TEAP 2005, Special Report on Safeguarding the Ozone Layer and the Global Climate System

Arctic Middle Atmosphere Chemistry

Overall goal of this theme To improve our understanding of the processes controlling

the Arctic stratospheric ozone budget and its future evolution, using measurements of the concentrations of stratospheric constituents.

This theme addresses two of the four “grand challenges in atmospheric chemistry” identified in the 2004 IGOS Atmospheric Chemistry Theme Report, namely

stratospheric chemistry and ozone depletion chemistry-climate interactions.

Arctic Middle Atmosphere Chemistry Theme

Science Questions What is the chemical composition of the Arctic stratosphere

above PEARL? How and why is it changing with time?

How is the chemistry coupled to dynamics, microphysics, and radiation?

What is the polar stratospheric bromine budget? Significant source of uncertainty BrO + ClO cycle estimated to contribute up to half chemical loss

How will the polar stratosphere respond to climate perturbations? Particularly while Cl and Br loading is high How will changes in atmospheric circulation affect polar ozone? Cooling (more ozone depletion) or warming (less)?


Scientific Objectives(1)To obtain an extended data set of the concentrations of ozone and of

other key trace gases in the Canadian Arctic stratosphere above PEARL under both chemically perturbed and unperturbed conditions.

(2)To analyse these measurements, in conjunction with dynamical, radiative, aerosol/PSC, and meteorological observations also made at PEARL, in order to unravel the coupled processes controlling Arctic stratospheric composition and to quantify the contributions from dynamics and chemistry to ozone depletion.

(3)To investigate the seasonal and interannual variability of the Arctic ozone budget, as well as its longer-term evolution, with a focus on determining the impact of climate change.

(4)To combine the measurements with atmospheric models (including chemical box models, chemical transport models and global circulation models) to facilitate both improved modelling of the atmosphere and the interpretation of the measurements, and hence to better understand climate system processes and climate change.


Short-Term Outputs

Better understanding of diurnal, day-to-day, seasonal, and interannual variations in a suite of Arctic stratospheric constituents, including ozone and related trace gases, particularly nitrogen and halogen compounds.

Identification and quantification of chemical ozone loss at Eureka during each Arctic winter-spring.

Process studies of the relative importance of chemical, radiative, microphysical, and transport processes, including comparisons with atmospheric models.


Long-Term Outputs

A significant new long-term dataset of Arctic chemical composition measurements.

Determination of trends in ozone and related stratospheric constituents.

Improved understanding of processes that result in feedbacks between stratospheric ozone depletion, rising greenhouse gas concentrations, and climate change.

Better predictive capabilities regarding the future evolution of the Arctic stratospheric ozone budget.


Primary Composition Instruments Bruker 125HR Fourier transform infrared spectrometer (FTS)

Direct solar (and lunar) absorption, 700-4500 cm-1 at high resolution

UV-visible grating spectrometer Zenith-scattered (and direct) solar absorption, 300-600 nm

Stratospheric ozone lidar Differential Absorption Lidar (DIAL)

Brewer spectrophotometer Ozone total columns

Polar Atmospheric Emitted Radiance Interferometer (P-AERI) Emission, 400-3300 cm-1 (3-25 µm) at low spectral resolution

Measurements Reactive species, source gases, reservoirs, dynamical tracers

O3, NO, NO2, HNO3, N2O5, NO3, N2O, ClONO2, HCl, OClO, BrO, HF, CFCs, CH4, H2O, CO, OCS, ...

Total columns and some information on vertical distribution

Modelling Interpretation will include comparisons with atmospheric

models in order to better understand the underlying processes and to facilitate improved modelling of the atmosphere. Comparisons with chemical transport models to quantify chemical

ozone loss, and the role of nitrogen, chlorine, and bromine families

Back trajectories and box models will be used to investigate the history and chemical evolution of stratospheric air above Eureka

CMAM can provide a detailed global chemical climate model, e.g., for estimating the spatio-temporal variability of the measured trace gases

CMAM-DA will enable combination of the Arctic data with other observations and with a priori information


DA8 FTS Measurements: HNO3

Farahani et al., JGR 2007

DA8 FTS Measurements: HNO3

Farahani et al., JGR 2007

Comparison of solar and lunar DA8 FTS measurements during winter 2001-2002 with SLIMCAT chemical transport model and CMAM

2006-2007 AMAC Highlights February-March 2006 - ACE Arctic validation campaign March 2006 - installation of SEARCH / U of Idaho AERI July 2006 - installation of new Bruker IFS 125HR FTS August 2006 - installation of new UV-visible grating

spectrometer (PEARL-GBS) August-October 2006 - first data from both instruments

February-March 2007 - ACE Arctic validation campaign May 2007 - P-AERI ordered July 2007 - Bruker / Bomem intercomparison campaign August-September 2007 - NDACC Aura validation campaign Ongoing - daily measurements, implementation and

optimization of retrieval algorithms, data analysis

AMAC Students and PDFs Bruker FTS measurements and data analysis

PDF Rebecca Batchelor, UofT MSc/PhD student Rodica Lindenmaier, UofT

UV-visible measurements and data analysis PhD student Annemarie Fraser, UofT PhD student Cristen Adams, UofT

Analysis of PARIS-IR & Bomem DA8 data using SFIT2 PDF Keeyoon Sung, UofT (Sept. 2006 - April 2007) PhD student Dejian Fu, U of Waterloo (just graduated)

Stratospheric ozone lidar measurements and data analysis MSc student Andrea Moss, UWO

2006 and 2007 ACE Arctic validation campaigns PDF Tobias Kerzenmacher, UofT

P-AERI measurements and data analysis PDF Mareile Wolff, UofT (IPY: Dec. 2007 - )

External Linkages Canadian Space Agency

Continues to support ACE Arctic validation campaigns, currently “Canadian Arctic Validation of ACE for IPY 2007 & 2008”

Network for the Detection of Atmospheric Composition Change (NDACC) Contacted Co-Chairs of the NDACC UV-Visible Working Group

about the requirements for certifying the UV-visible spectrometer Invited to upcoming November meeting

Comparing Bruker FTS with Bomem DA8 for NDACC certification Six weeks of alternating measurements from February-March

2007, linked by continuous measurements with PARIS-IR Additional intercomparison campaign held in July 2007

Actively collaborating with Gloria Manney, JPL Working on linkages with SEARCH, IASOA, SPARC,

modelling groups

AMAC-Related Publications* T.E. Kerzenmacher et al., Measurements of O3, NO2 and Temperature During the 2004 Canadian

Arctic ACE Validation Campaign. GRL 2005.A. Wiacek et al., First Detection of Meso-Thermospheric Nitric Oxide by Ground-Based FTIR Solar

Absorption Spectroscopy. GRL 2006.E.E. Farahani et al., Nitric acid measurements at Eureka obtained in winter 2001-2002 Using solar

and lunar Fourier transform infrared absorption spectroscopy: Comparisons with observations at Thule and Kiruna and with results from three-dimensional models. JGR 2007.

* G. L. Manney et al., The high Arctic in extreme winters: vortex, temperature, and MLS and ACE-FTS trace gas evolution. ACPD 2007.

* R. J. Sica et al., Validation of the Atmospheric Chemistry Experiment (ACE) version 2.2 temperature using ground-based and space-borne measurements. ACPD 2007.

R. Lindenmaier, First Measurements of ozone with the new Bruker IFS 125HR at Eureka, M.Sc. Thesis, U of Toronto, Toronto, 2007.

* D. Fu et al., PARIS-IR and ACE Measurements, Ph.D. Thesis, U of Waterloo, 2007. * A. Fraser et al., Intercomparison of UV-visible measurements of ozone and NO2 during the

Canadian Arctic ACE Validation Campaigns: 2004–2006. In preparation. Submission to ACP is imminent.

* E. Dupuy et al., Validation of ozone measurements from the Atmospheric Chemistry Experiment (ACE). Submission to ACP is imminent.

* K. Sung et al., Partial and total column measurements at Eureka, Nunavut in spring 2004 and 2005 using solar infrared absorption spectroscopy, including comparisons with ACE satellite measurements. Submission to ACP soon.

* D. Fu et al., Simultaneous atmospheric measurements using two Fourier transform infrared spectrometers at the Polar Environment Atmospheric Research Laboratory (PEARL) during spring 2006. Submission to ACP soon. * Also ACE validation

TCCON Opportunity Invited to join proposal to NASA for expansion of the Total

Carbon Column Observing Network (TCCON) Network of Bruker 125HRs for CO2, CH4, H2O, O2, N2O, CO

One goal - validation of NASA's Orbiting Carbon Observatory (OCO) Travel and loan of hardware (beamsplitters, detectors, data storage)

Attended TCCON meeting at May NDACC IRWG meeting Provided a report to CANDAC Scientific Steering Committee Recommended that we accept the invitation to join the network

Issues TCCON measurements use different beamsplitter and detector from

standard mid-IR configuration, with manual intervention needed Some reduction in "middle atmosphere" observations

General thoughts An interesting and positive extension of our capabilities, benefits

outweigh challenges, links us to this growing network, very topical

Outlook: Tasks and Issues Installation of new sun-trackers for FTS and UV-visible Maximization and automation of Bruker FTS

measurements Upgrade and operation of stratospheric ozone lidar Installation of CANDAC P-AERI NDACC certification for Bruker FTS and UV-visible

spectrometer Implementation of TCCON capability if proposal successful Completion of the analysis of Bomem DA8 data archive Analysis of CANDAC/PEARL measurements Integration with complementary measurements at PEARL Contributions to IPY atmospheric science

overview of the arctic middle atmospheric chemistry theme

Documents

ozone budgetcoupled

averageswmo ozone assessment

marchwmo ozone assessment

arctic vortex

ozone losslarge variation

monthly averaged total

arctic ozone short long

vortex centre