1. Towards IPCC AR6: Open questions in chemistry-climate coupling
What are the environment / sustainability questions that the highest levels of governments will ask ?
Which of these requires input from ACC community ?
Ozone depletion (recovering or not?)
Air quality (local control? out of our control?)
Climate change (is this just CO2?)
Geoengineering the stratosphere (complexity?)
Who will be asking these questions ? How ? When ?
UNFCCC COP
Related multi-lateral climate talks
UNEP O3, LRTAP, …
Thru IPCC AR6 or Special Reports, probably 2019+
(e.g., on AQ & Climate)
Will the ACC community be able to answer ?
N.B. Warning label, this is just Prather’s editorial viewpoint.
4 Jan h
Towards IPCC AR6: Open questions in chemistry-climate coupling
Michael Prather, UC Irvine
CCMI 2014 May Lancaster UK

2. Carefully specify the question. Plan for what it takes to answer it.
CCMI => AR6: M. Prather 20 May 2014 Lancaster
What can CCMI do ?
Carefully specify the question.
Plan for what it takes to answer it.
Design innovative experiments.
Establish standard diagnostics
to compare with observations (specific to Q)
to diagnose model differences (sensitivities)

3.   How to build a robust understanding of future AQ ?
CCMI => AR6: Innovative Experiments M. Prather 20 May 2014 Lancaster
How to build a robust understanding of future AQ ?
Global emissions alter atmospheric composition and thence baseline levels (lowest percentiles) of near-surface O3 and particulate matter (PM)
Global changes in climate (e.g., temperature, water vapor, convection, lightning) also alter these baselines
Climate-driven changes in the meteorological regimes over polluted regions can alter extreme air quality (AQX) episodes
Climate-change alters the efficacy of local, controlled emissions to generate pollution within a governance region (e.g., AQMD, EU country) via T, q, biogenic VOCs, radiation.
With all factors combined (as typical in most pubs) verification is effectively impossible, also is understanding model differences. An assessment approach needs to evaluate each of these pieces separately using observations/ensembles (HTAP 2010; IPCC, 2013).  

4.  How to build a robust understanding of future AQ ?
CCMI => AR6: Innovative Experiments M. Prather 20 May 2014 Lancaster
How to build a robust understanding of future AQ ?
Global emissions alter atmospheric composition and thence baseline levels (lowest percentiles) of near-surface O3 and particulate matter (PM) (Young et a; 2013 ACP). 
(surface) / ppb

5. CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster
ACCMIP hourly surface O3 diagnostics: Model tests with full EU/US surface sites from J. Schnell et al 2014 ACPD++ , UC Irvine
surface AQ O3 sites gridded for comparison with ACCMIPs
Test 2000s decade of ACCMIP for:
seasonal cycles diurnal cycles AQX (97th %ile)
eastern US
western

6. Bad years have: (1) most AQX, (2) largest episodes,
CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster
Mega-pollution episodes caused by continental-scale stagnation episodes: change with climate?
Recent work on mapping out local climatologies of surface O3 show extensive, multi-day (mega) pollution episodes from surface sites, & possibly satellite.
Air Quality Extreme (AQX) events [red 1x1 cells],
when identified as 97%ile form mega-episodes,
=> matched by global model hindcast.
Bad years have: (1) most AQX, (2) largest episodes,
and (3) highest mean O ? Bad climates do also?
US Climatology of O3 Air Quality & extreme episodes (AQX)
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009 R2
AQX events (#)
13.5
11.5
16.5
15.0
4.6
11.2
13.3
8.1
1.7 1
AQX size (hkm2 d)
618
373
1239
581 82
435
515
186 70 32
0.78
O3 JJA
(ppb)
49.3
49.4
51.4
50.1
45.5
48.8
50.7
47.5
46.2
43.7
0.96
Schnell ++, 2014 ACPD (current)

7. Serious Climate Change is just about the CO2.
CCMI => AR6: Why chemistry matters M. Prather 20 May 2014 Lancaster
Serious Climate Change is just about the CO2.
With a “likely to avoid 2°C” cap of 1,000 GtC, and 500 GtC already spent, we have headroom of 500 GtC
With CH4, O3, N2O, HFCs, the cap is only 790 GtC and then the headroom drops 42% to 290 GtC!

8. What is really going on in the stratosphere? N2O lifetime change
CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster
What is really going on in the stratosphere? N2O lifetime change
from E. Fleming, GSFC
Uncertainty in the future N2O lifetime is a
major part of the IPCC AR5 range in future
N2O abundances for a given scenario,
impacting both climate and ozone.

9. Diagnosing lower strat vs. upper trop with a state variable like e90
CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster
Diagnosing lower strat vs. upper trop with a state variable like e90
Use of artificial tracer e90 can diagnose
tropopause (white line) and identify /
separate many features such as folds,
tubes, and even an undiscovered N-S
systematic difference in O3:
Prather, et al.,2011 JGR 116, D04306
O3 (ppb, annual) wrt tropopause
height
50S-40S << 40N-50N
+4 km
731
993
+1 km
147
234
tpp
118
203

10. CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster
Where is the equator? a diagnostic definition based on atmospheric mixing from C. Holmes & M. Prather, UC Irvine
Seasonal cycles of trop-hemisphere mass and trop-chemistry loss of CH4
CH4 column loss & mixing equator (30 days)
Atmospheric-mixing equator defined as where NH and SH e90 tracers are equal (actually baroclinic). This equator moves with seasons & the monsoons
On average 53% of the troposphere is in SH
CH4 loss freq. is 25% faster in geographic NH
CH4 loss freq. only 5% faster in atmos-mix NH
MCF obs. only constrain this latter !
N.B. the Waugh-Orbe tracers (Orbe et al, 2013 JGR) are similar to the e90 tracers (Prather et al, 2011 JGR).

11. CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster
Trop. chemistry has scales and variability not simply diagnosed as mean and std dev. How should model validation go after this? UCI CTM (T319L60) 16 Jan 2005
Loss O3 (ppb/day)
Go after the key rates! Observe / diagnose those species needed to derive P/L – O3, L – CH4, ….
Generate prob. distrib. and other statistics.
Prod O3 (ppb/day)
H2O2 (ppb on 720 hPa)
Loss freq CH4 (/year)
Loss freq CH4 (/year)

12. CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster
What is the STE flux of O3 from strat to trop ? Where and when does it occur ?
Can we even agree on how to calculate it in a model ? How to detect change ?
It is exceedingly difficult to calculate the STE flux of O3 – even within in models, much less to “observe” it. All “measurements” are proxies. O3-tracer correlations is best integrative method.
Tracer-tracer slope gives relative fluxes (Plumb & Ko,1992)
When STE is diagnosed with high spatial and temporal resolution, we can identify (at least in the models) new processes that are linked to STE: e.g., continental convection in NH summer (Tang, 2011, GRL).
Fig. Latitude‐longitude plot of mean deep convective fluxes (colored pixels at model resolution, hPa/s) and STE O3 fluxes (red contour lines, g/m2/yr) for JJA of 2005.

13. CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster
What is the STE flux of O3 from strat to trop ? Where and when does it occur ?
Can we even agree on how to calculate it in a model ? How to detect change ?
Three commonly used STE O3 flux diagnostics are compared within a single CTM running ECMWF IFS meteorology from very different versions: Cycle 29/31 & Cycle 36 (stagnant).
Tropopause is diagnosed with e90 synthetic tracer.
TC measures advective change in trop O3 column every step across an iso-surface.
LS calculates monthly budgets for lowermost strat: 100 hPa to a lower iso-surface.
WxO3 calculates flux across 100 hPa every step or using monthly zonal mean circ.
the residual circ. monthly zonal means is [w*] x [O3]
STE fluxes with TC and LS are similar, but [w*] does not even give interannual variability

14. CCMI => AR6: Innovative Experiments. M
CCMI => AR6: Innovative Experiments M. Prather 20 May 2014 Lancaster
How important is STE O3 flux? What is the lifetime of trop O3 from different sources (surface pollution, lightning NOx, STE)? Young et al 2013, ACP
ΔτO3
We know that the perturbation lifetime for trop O3, depends on the source: Δτ = ΔB / Source
Otherwise, why care about STE flux? (ΔτSTE > ΔτP
~ >> >>

15. is this schmutz ours or can we blame it on….?
CCMI => AR6: M. Prather 20 May 2014 Lancaster
forecast for LA
clear skies, but
is this schmutz ours or can we blame it on….?
LA and HOLLYWOOD sign from UCIrvine 7 Mar h