Intercontinental Transport of Anthropogenic and Biomass Burning Pollution

1
Intercontinental Transport of Anthropogenic and
Biomass Burning Pollution
Qinbin Li Department of Earth and Planetary Scien
ces
Harvard University March 2003
2
Statement of problem

• Intercontinental transport of anthropogenic and
  biomass burning pollution, particularly ozone,
  could have important impact on global atmospheric
  chemistry and regional air quality that needs to
  be better understood and quantified.

Middle East ozone maximum. Li et al., GRL,
2001 Springtime ozone maximum at Bermuda. Li et
al., JGR, 2002b Export efficiency of NOy out of
continental boundary layer. Li et al., JGR,
2003b Transatlantic transport of pollution. Li
et al., 2002a Atmospheric budgets of biomass bur
ning tracers HCN and CH3CN. Li et al., GRL,
2000 Li et al., JGR, 2003a
3
Approach
GEOS-CHEM global 3-D model simulation
Tagged tracers (CO, ozone) Sensitivity simulati
on
Tracer correlations
Tropical easterly
Midlatitude westerly
TRACE-P
MOZAIC
NARE
Sonde
Mace Head
Sable Island
Bermuda
ASIA
NORTH AMERICA
EUROPE
NORTH PACIFIC
NORTH ATLANTIC
MIDDLE EAST
4
GEOS-CHEM and limited observations indicate an
ozone maximum over the Middle East
circles ozonesonde/MOZAIC contours
GEOS-CHEM (July 1997)
What is the origin of this ozone maximum?
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Origin of the Middle East ozone maximum
GEOS-CHEM, July 1997
arrows ozone transport flux contours ozone prod
uction rate
Combination of three factors anticyclonic circul
ation in the middle/upper troposphere with
large-scale subsidence over the Middle East.
lightning outflow from the India monsoon and
pollution from China transported in an easterly
tropical jet. northern midlatitude pollution tran
sported in the westerly midlatitude jet.
6
Recent confirmation of the Middle East ozone
maximum SAGE II tropospheric ozone observation
July
October
Climatological ozone mixing ratio at 7 km from
SAGE II
(1985-90, 1994-99)
Kar et al. 2002
7
Interpretation of the springtime ozone maximum at
Bermuda
?
? Stratospheric Oltmans Levy II, 1992,1994
Moody et al., 1995 ? Anthropogenic Dickerson et
al., 1995
GEOS-CHEM reproduces the observed seasonal cycle
of surface ozone at Bermuda.
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Transport of North American pollution to Bermuda
in spring
Observations are from S. Oltmans
r 0.82, bias -1.8 ppb
Source attribution in the model
Most of surface ozone at Bermuda in spring
originates from North American (outflow behind
cold fronts) stratosphere contributes less than
5 ppb.
Li et al. 2002
9
Previous argument for stratospheric origin of
ozone at Bermuda from back-trajectory analyses
Oltmans and Levy II 1994 On days with high
ozone the trajectories all come from north of
50N and altitudes near 600 mb.
Moody et al. 1995 High-ozone events are
associated with high-speed subsident flow of
North American continental origin.
Moody et al. 1995
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GEOS-CHEM reproduces the association of high
ozone at Bermuda with subsiding trajectories
from NW
March 18, 1996 event 290 K back-trajectory
Subsiding air
Cold front
Ozone pollution
N. America
Bermuda
Continental ozone pollution mixes with subsiding
air behind cold fronts
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North Atlantic Regional Experiment (NARE97) NOy
export efficiency (f) out of continental boundary
layer
Lagrangian along NARE97 flight tracks
f 9, NOx/NOy 8
Parrish et al., 2003
Eulerian NOy export flux out of CBL
f 30, NOx/NOy 34
Liang et al., 1998
Lagrangian mixing model f (?NOy/?CO) R a
f NOy export efficiency ?NOy, ?CO enhanc
ement over background
R anthropogenic emission ratio CO/NOy
a natural CO enhancement in CBL
12
NOy export efficiency (f) out of the North
American boundary layer NOy-CO correlations
along the NARE97 flight tracks
Curves relationships expected from the mixing
model for different values of the export
efficiency of NOy (f).
13
NOy export efficiency (f) Reconciling Eulerian
and Lagrangian analyses
Liang et al. 1998 f 30,NOx/NOy 34 Euleri
an
Parrish et al. 2003 f 95, NOx/NOy 8 La
grangian, (1) f 14.511 Lagrangian, (1) b
ut CO 95 ppb f 1713 Lagrangian, (2) but
NOy 0.1 ppb
This work f 11.53 Lagrangian, (1) f 1
77 Lagrangian, (2) f 176, NOx/NOy 6
4 Lagrangian, (2) but model ?CO, ?NOy f
20, NOx/NOy 39 Eulerian
(1) background CO 75 ppb, NOy 0.1 ppb R
5.67 a 1.18 Parrish et al., 2003
(2) background CO 95 ppb, NOy 0.3 ppb R
6.50 a 1 GEOS-CHEM
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Ozone production due to exported North American
anthropogenic NOy
GOES-CHEM, September 1997
Half the ozone production takes place in
near-field driven by exported NOx the other half
is due to exported PAN over NH.
The eventual ozone production due to exported NOy
is comparable to direct export of ozone
pollution.
15
Transatlantic transport of North American
pollution Simulated concentrations and fluxes o
f North American pollution ozone
GEOS-CHEM 1997
L
April
H
L
July
H
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Surface ozone at Mace Head, IrelandNorth
American pollution signal is there but faint
Model vs. observed stats, 1993-1997
Time series, Mar-Aug 1997
GEOS-CHEM
N. America pollution events in the model
Observation
Li et al. 2002
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Effect of North American sources on violations of
European air quality standard (55 ppbv, 8-h
average)
GEOS-CHEM, JJA 1997
of violation days (out of 92)
of violation days that would not have been in
absence of North
American emissions
18
Transport of North American pollution to Europe
Correlation with the NAO Index
NAOI normalized surface pressure anomaly between
Iceland and Azores
North American ozone pollution enhancement at
Mace Head, Ireland (GEOS-CHEM)
North Atlantic Oscillation (NAO) Index
r 0.57
Greenhouse warming a NAO index shift a change in
transatlantic

transport of pollution
19
Intercontinental transport of pollution Surface
ozone enhancements caused by anthropogenic
emissions from different continents
GEOS-CHEM, JJA 1997
North America
Europe
Asia
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Atmospheric HCN Tracer for long-range transport
of biomass burning pollution?
Conventional view source biomass burning Lob
ert, 1990 sink reaction with OH lifetime 2-
5 years well mixed 150-170 pptv Cicerone a
nd Zellner, 1983
Rinsland et al. 1998
Recent observations indicate a much shorter
lifetime (less than a year) missing sink?
Zhao et al. 2000
21
Proposed atmospheric budget for HCN
(atmospheric lifetime 2 - 4 months)
26 km
HCN h? HCN O(1D) HCN OH 0.1 Tg N yr-1
Tropopause
HCN OH 0.2 Tg N yr-1
HCN
Ocean uptake 1.1-2.6 Tg N yr-1
(saturation HCN(aq)/CN-
Biomass burning 1.4-2.9 Tg N yr-1
k 0.2 yr-1
Henrys law constant (298 K) 8-12 M atm-1
pKa(HCN(aq)/CN-) 9.2
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TRACE-P observations of background (COC2Cl4uptake sink
GEOS-CHEM, Feb-Apr 2002
Deposition velocity 0.13 cm s-1
Saturation ratio 0.79 for HCN, 0.88 for CH3CN
Model reproduces the vertical gradients between
MBL and FT.
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TRACE-P observations of HCN-CH3CN-CO
GEOS-CHEM Feb-Apr 2002
HCN
Elevated HCN in Chinese urban plumes.
CH3CN
Relatively small enhancements of CH3CN in Chinese
urban plumes.
CO
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Atmospheric budgets of HCN and CH3CN
GEOS-CHEM 2002
CH3CN is a better tracer for biomass burning.
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Summary of results

• Middle East ozone maximum is attributed to
  lightning outflow from India and pollution from
  China transported in a tropical easterly jet Li
  et al., GRL, 2001.
• The springtime ozone maximum at Bermuda is
  attributed to boundary layer outflow of North
  American pollution behind cold fronts, not to
  stratospheric sources Li et al., JGR, 2002b.
• Export efficiency of NOy out of continental
  boundary layer from Eulerian and Lagrangian
  approaches are consistent (20). Ozone
  production due to exported NOy is comparable to
  direct export of ozone pollution Li et al., JGR,
  2003b.
• Transatlantic transport of pollution North
  American anthropogenic emissions enhance surface
  ozone in Europe by 2-5 ppb on average in summer
  which is important for European air quality
  standard. The NAO index is a predictor for
  transatlantic transport of North American
  pollution Li et al., JGR, 2002a.
• Atmospheric budgets of HCN and CH3CN ocean
  uptake is a dominant sink for both HCN and CH3CN
  CH3CN is a better biomass burning tracer Li et
  al., GRL, 2000 Li et al., JGR, 2003a.