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Satellite-detection and attribution of rapid increases in tropospheric ozone made in China and its influence on the western United States
Folkert BoersmaNow also at
A short story about ozone made in China
SubmittedWillem W. Verstraeten1,2,3*, K. Folkert Boersma1,2,3, Jason E. Williams1, Jessica L. Neu4, Kevin W. Bowman4 and John R. Worden4
Impact of (SRES-A2) emissions (in ppb)
2030 – 2000
Loss in life expectancy in monthsSource: EU programme CAFE, CAFE Scenario Analysis Report Nr. 2. (Amann et al., 2004)
Szopa et al., 2004
Why do we care about ozone in the troposphere?
I live here
1. Ozone is an air pollutant – also in Europe
Shindell et al., 2009
Why do we care about ozone in the troposphere?
2. Ozone is the 3rd most powerful cause of positive radiative forcing
O3 RF: 0.40 W/m2 CO2 RF: 1.69 W/m2
…but uncertainty in ozone forcing (±0.20 W/m2) higher than for CO2 and CH4
Why do we care about ozone in the troposphere?
3. Ozone drives the oxidative capacity of the atmosphere
O3 + hv O2 + O(1D)O(1D) + H2O 2 OH
OH is the “detergent” of the atmosphere, determining lifetime of CH4, CO, and many other pollutants
Need to understand ozone to improve our understanding of OH and possible trends therein
Model-result: OH very difficult to measure!
IPCC AR5-reported trends in tropospheric ozone
IPCC conclusions• Ozone increases over Europe and eastern USA have levelled off• Ozone has likely increased over eastern Asia since the 1990s
Ozone increases over western United States
• Compile and analyse large dataset (1984-2008) of ozone measurements over the western United States
• Ozonesondes, lidar, aircraft measurements
Cooper et al., 2008
EU air quality standard
Unclear where that ozone came from
High ozone tends to originate from deep within Asia
LOW OZONE CONDITIONS
HIGH OZONE CONDITIONS Ozone monitoring in the free troposphere since the 1970s is very limited.
What can satellite instruments tell us?
Observes NO2 in VIS
Surface
l1 l2
Scattering by Earth surface and by atmosphere
Satellite instruments: TES and OMI
Observes ozone in thermal IR
SurfaceTo
Il(T0)
blackbodyradiation
absorbing gasT1
elIl(T1)
Broadly sensitive to
free tropospheric ozone
Sensitive to NO2
down to the surface
Vertical sensitivity
464 hPa averaging kernel:Broad sensitivity to free tropospheric ozone
OMI: sensitivity down to surface
Validation and use of TES ozone retrievals
Global map of summertime tropospheric ozone from TES (@464 hPa)
Strong precursor emissions!+ photochemical activity
JJA2005-2010464 hPa
Validation and use of TES ozone retrievals
Global validation with WOUDC ozone sondes for period of 6 years
• Insignificant trend in TES-sonde bias at midlatitudes• TES can be safely used for temporal analysis
Verstraeten et al., AMT, 2013
Increase in Summertime tropospheric O3 and NO2 observed by TES and OMI over China
2005-2006: May-August 2009-2010: May-August 2010-2005 Difference
• TES: Strong increase in FT ozone over and downwind of China• OMI: Strong increase in BL NO2 pollution over China
TES 464 hPa
Increase of 1.1 ppbv/yr ozone 0.0
15.0
30.0
45.0
60.0
75.0
90.0
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73
Months
Mo
nth
ly o
zo
ne V
MR
at
46
4 h
Pa
-18
-12
-6
0
6
12
18
24
30
36
42
48
Mo
nth
ly a
no
maly
ozo
ne V
MR
at
46
4
hP
a
TES Anomaly TES Lineair (Anomaly TES)
Increase of 1.1 ppbv ozone/yr at 464 hPa
TES 3-9 km partial ozone column 2009-2010
Also increasing but not at a statistically significant pace
Increase in tropospheric O3 observed by TES over western United States
Interpretation of the increases with TM5 CTM
Research Question 1: Can emissions explain the increase in FT O3 over/downwind of China?
3-D global chemistry transport model• 34 vertical layers (surface-0.1hPa), 3˚×2˚• ECMWF meteorological fields (ERA-interim)
Emission inventories: • Anthropogenic inventories: RETRO project + REAS inventory for Asian • Lightning NOx emissions: ~5 Tg N/yr• Biomass burning emissions: GFEDv2• Tropospheric chemistry: 42 species and > 60 reactions (CBM-IV)• Reference: Huijnen et al., 2010.
2 TM5 simulations:1. Invariable NOx emissions2. OMI-constrained NOx emissions
OMI-constraints on NOx emissions (2005-2010)
• Update a priori emissions to follow OMI-observed trend• Update for all grid cells (no smearing)• Take into account non-linear sensitivities to chemical regime
NO2
OMI,2006
OMI,2006jOMI,2006j Ω
ΩΩβ1EE
New top-down emissions
A priori emissions
Change in year j relative to 2006 in NO2 observed with OMI
Sensitivity of NO2 column to changing emissions
Taking into account chemical regime (β)
Evaluate TM5 response to perturbing NOx emissions (Lamsal et al., 2009):
TM5,2006
TM5,2006
Ω
ΔΩβ
E
ΔE
β=1: linear local response between NOx and NO2 columnβ>1: Rapid negative feedback on NO2 via increased OHβ<1: Accumulation of NO2 in response to emissions
JANUARY
JULY
Increasing emissions by +15%
In winter: β<1 (long lifetime NO2)In summer: β>1 (enhanced loss)
OMI-constrained NOx emissions (2010-2005)
Clean-up of USA, Europe and Japan Strong increases in Asia
OMI-constrained NOx emissions over China (2010-2005)
y = 0.0144x + 3.1972
R 2 = 0.035
y = 0.0142x - 0.5179
R 2 = 0.3057
-2.0
0.0
2.0
4.0
6.0
8.0
10.0
1 13 25 37 49 61 73Months since J anuary 2005
OM
I tr
op
.NO
2 1
0-1
5 m
ole
c/cm
2
Mean China Anomaly Lineair (Mean China) Lineair (Anomaly)
5.4% / yr
y = 0.0144x + 3.1972
R 2 = 0.035
y = 0.0142x - 0.5179
R 2 = 0.3057
y = 0.0268x + 2.4192
R 2 = 0.0849y = 0.0032x + 2.0221
R 2 = 0.0091
-2.0
0.0
2.0
4.0
6.0
8.0
10.0
1 13 25 37 49 61 73Months since January 2005
OM
I tr
op
.NO
2 1
0-1
5 m
ole
c/cm
2
Mean China Anomaly TM5_ ref TM5_ upd
Lineair (Mean China) Lineair (Anomaly) Lineair (TM5_ upd) Lineair (TM5_ ref)
5.4% / yr
TM5 with OMI emissions captures OMI time series
Reproducing the TES-observed O3 increase over China
TM5 with updated OMI emissions better captures TES time series
But substantial increase also in TM5 simulation with constant NOx emissions
Stratosphere-troposphere exchange (STE) over China
Research Question 2: What is the role of stratosphere-troposphere exchange?
Use TM5• Stratospheric ozone in TM5 is constrained by 30-year
(assimilated) 14-satellite dataset of total ozone (van
der A. et al., ACP, 2010)• Net stratosphere-troposphere exchange is governed
by ECMWF meteo + MSR constraints• STE can be tracked in TM5 with tagged tracer ‘O3S’O3 increase due to STE Overall O3 increase
2010-2005 differenceChina
2010-2005 differenceChina
Stratosphere-troposphere exchange (STE)
Deseasonalized changes in tropospheric ozone
Answers to Research Questions:• STE and increasing NOx both explain
the observed increase over China • STE stronger effect
From subtracting TM5 simulations 1 and 2 (same STE)
What is happening with O3 over the western United States?
TES 3-9 km partial ozone column 2009-2010
Also increasing but not at a statistically significant pace
Reduced NOx emissions …
Substantial reductions in NOx emissions over the western USA (-12% between 2005-2010)
Overall O3 increase O3 increase due to STE
…but also strong O3 increase due to STE over the western USA
STE associated with enhanced stratospheric circulation in response to vigorous El Nino & QBO in 2010 relative to 2005
2005-2010 ozone changes over the western US
Deseasonalized changes in tropospheric ozone: increase!
• TES indicates increase over western US• In spite of local decreases in NOx
• STE masks out effects reductions in anthropogenic NOx emissions
How much of the western US ozone increase originated from China?
Compare two 6-year TM5 simulations
2. TM5 with OMI-constrained NOx emissions throughout the world3. As (2) but with constant REAS-2006 NOx emissions over China
Difference between (2) and (3) indicative of the effect of increasing Chinese NOx emissions on western United States
Change in Anthropogenic NOX emissions between 2010 and 2006
ΔO3 due to increasing Chinese NOx emissions
ΔO3 between 2010 and 2005 at ~900 hPa (±1 km)
Western US O3 increases by +0.1 ppbv at ±1 km because of +15% Chinese NOx emission increases
ΔO3 between 2010 and 2005 at ~460 hPa (±6 km)
Western US O3 increases by +0.2 ppbv at ±6 km because of large-scale transport & sustained O3 production driven by decomposition of nitrogen reservoirs in descending air masses
ΔO3 due to increasing Chinese NOx emissions
Deseasonalized timeseries 3-9 km correcting for STE and local effects
FT (3-9 km) O3 increases by 0.01 DU/yr (0.1%/yr)
This import neutralizes one-third of the O3 decreases related to reduction in surface emissions due to stricter air pollution policies.
Discussion
• Combined use of TES and OMI provides a new perspective on changing tropospheric composition in 2005-2010
• TES observes a 10% increase in 6 years in FT O3 over China• Supported by TM5 when OMI-constrained NOx (+2%) and STE
changes (+8%) are accounted for
• TES indicates a 4% increase in FT O3 over western US• Policy-driven NOx reductions alone would have reduced O3 (-1%)
over the western US in the absence of other effects• STE (+5%) and import of ozone made in China (+0.5%) offset
local policy measures
Support for increased STE over China throughout 2005-2010
Wang et al, 2012, ACP
OZONE SONDES OVER BEIJING
--- Sonde: influenced by photochemical production and STE--- Model (CLaMS): only STE