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Intercontinental Transport of Anthropogenic and Biomass Burning

Pollution

Qinbin Li

Department of Earth and Planetary SciencesHarvard University

March 2003

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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.

1. Middle East ozone maximum. [Li et al., GRL, 2001]

2. Springtime ozone maximum at Bermuda. [Li et al., JGR, 2002b]

3. Export efficiency of NOy out of continental boundary layer. [Li et al., JGR, 2003b]

4. Transatlantic transport of pollution. [Li et al., 2002a]

5. Atmospheric budgets of biomass burning tracers HCN and CH3CN. [Li et al., GRL, 2000; Li et al., JGR, 2003a]

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ApproachGEOS-CHEM global 3-D model simulation:• Tagged tracers (CO, ozone)• Sensitivity simulation • Tracer correlations

NARETRACE-P

ASIA NORTH AMERICA

EUROPENORTH PACIFIC

NORTH ATLANTIC

Midlatitude westerly

MIDDLE EAST

Tropical easterly

MOZAIC

Mace Head

Sable Island Bermuda

Sonde

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GEOS-CHEM and limited observations indicate an ozone maximum over the Middle East

What is the origin of this ozone maximum?

circles: ozonesonde/MOZAIC contours: GEOS-CHEM (July 1997)

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Origin of the Middle East ozone maximum

GEOS-CHEM, July 1997

Combination of three factors:

• anticyclonic circulation 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 transported in the westerly midlatitude jet.

arrows: ozone transport fluxcontours: ozone production rate

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Recent confirmation of the Middle East ozone maximum: SAGE II tropospheric ozone observation

Kar et al. [2002]

Climatological ozone mixing ratio at 7 km from SAGE II (1985-90, 1994-99)

July October

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Interpretation of the springtime ozone maximum at Bermuda

GEOS-CHEM reproduces the observed seasonal cycle of surface ozone at Bermuda.

? Stratospheric [Oltmans & Levy II, 1992,1994; Moody et al.,

1995]

? Anthropogenic [Dickerson et al., 1995]

?

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Li et al. [2002]

Most of surface ozone at Bermuda in spring originates from North American (outflow behind cold fronts); stratosphere contributes less than 5 ppb.

Observations are from S. Oltmans

Transport of North American pollution to Bermuda in spring

r = 0.82, bias = -1.8 ppb

Source attribution in the model

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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 50°N 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

Continental ozone pollution mixes with subsiding air behind cold fronts

N. America

Cold front

Ozone pollution

Subsidingair

Bermuda

March 18, 1996 event:290 K back-trajectory

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North Atlantic Regional Experiment (NARE’97): NOy export efficiency (f) out of continental boundary layer

Lagrangian mixing model:

f = (∆NOy/∆CO) • R • α

f : NOy export efficiency ∆NOy, ∆CO: enhancement over background R: anthropogenic emission ratio CO/NOy

α: natural CO enhancement in CBL

Lagrangian: along NARE’97 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]

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NOy export efficiency (f) out of the North American boundary layer: NOy-CO correlations

along the NARE’97 flight tracks

Parrish et al. [2003] this work

NOy export efficiency (f) 9±5% (→ 17±13%) 11.5±3% (→ 17±7%)

as NOx 8% 6±4%

as PAN 34% 36±13%

as HNO3 57% 52±14%

Curves: relationships expected from the mixing model for different values of the export efficiency of NOy (f).

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Liang et al. [1998]

f = 30%,NOx/NOy = 34%Eulerian

Parrish et al. [2003]

f = 9±5%, NOx/NOy = 8% Lagrangian, (1)

f = 14.5±11%Lagrangian, (1) but CO = 95 ppb

f =17±13%Lagrangian, (2) but NOy = 0.1 ppb

This work

f = 11.5±3%Lagrangian, (1)

f = 17±7%Lagrangian, (2)

f = 17±6%, NOx/NOy = 6±4%Lagrangian, (2) but model ∆CO, ∆NOy

f = 20%, NOx/NOy = 39%Eulerian

NOy export efficiency (f): Reconciling Eulerian and Lagrangian analyses

(1) background CO =75 ppb, NOy = 0.1 ppb; R = 5.67; α = 1.18 [Parrish et al., 2003]

(2) background CO =95 ppb, NOy = 0.3 ppb; R = 6.50; α = 1 [GEOS-CHEM]

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Ozone production due to exported North American anthropogenic NOy

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.

GOES-CHEM, September 1997

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April

July

Transatlantic transport of North American pollution:Transatlantic transport of North American pollution: Simulated concentrations and fluxes of North American pollution ozoneSimulated concentrations and fluxes of North American pollution ozone

GEOS-CHEM 1997

L

L

H

H

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Surface ozone at Mace Head, Ireland:North American pollution signal is there but faint

GEOS-CHEM N. America pollutionevents in the model

Time series, Mar-Aug 1997 Model vs. observedstats, 1993-1997

Li et al. [2002]

Observation

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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 thatwould not have beenin absence of North American emissions

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North Atlantic Oscillation (NAO) Index

North American ozone pollution enhancement at Mace Head, Ireland (GEOS-CHEM)

r = 0.57

NAOI: normalized surface pressure anomaly between Iceland and Azores

Transport of North American pollution to Europe: Correlation with the NAO Index

Greenhouse warming NAO index shift change in transatlantic transport of pollution

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GEOS-CHEM, JJA 1997

North America

Europe

Asia

Intercontinental transport of pollution: Surface ozone enhancements caused by anthropogenic emissions

from different continents

20Zhao et al. [2000]

Atmospheric HCN: Tracer for long-range transport of biomass burning pollution?

Conventional view: source: biomass burning [Lobert, 1990]

sink: reaction with OH lifetime: 2-5 years well mixed: 150-170 pptv [Cicerone and Zellner, 1983]

Recent observations indicate a much shorter lifetime (less than a year) – missing sink?

Rinsland et al. [1998]

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Proposed atmospheric budget for HCN(atmospheric lifetime = 2 - 4 months)

HCN(aq)/CN-

HCN

Biomass burning1.4-2.9 Tg N yr-1

Ocean uptake 1.1-2.6 Tg N yr-1

(saturation < 0.85)

Tropopause

Henry’s law constant (298 K) = 8-12 M atm-1

pKa(HCN(aq)/CN-) = 9.2

HCN + OH 0.2 Tg N yr-1

26 km

HCN + OH 0.1 Tg N yr-1

HCN + O(1D) < 0.01 Tg N yr-1

HCN + hν < 0.01 Tg N yr-1

k > 0.2 yr-1

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TRACE-P observations of background (CO<120 ppb, C2Cl4<10 ppt) HCN and CH3CN:

A dominant ocean uptake sinkGEOS-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

HCN

CO

CH3CN

GEOS-CHEM Feb-Apr 2002

Elevated HCN in Chinese urban plumes.

Relatively small enhancements of CH3CN in Chinese urban plumes.

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HCN CH3CN

Atmospheric burden (Tg N) 0.426 0.28

Atmospheric lifetime (months) 6.2 6.7

Tropospheric burden (Tg N) 0.38 0.25

Tropospheric lifetime (months) 5.3 5.8

Sources (Tg N yr-1)

Biomass burning 0.63 0.47

Residential coal burning

0.20 0.03

Sinks (Tg N yr-1)

Ocean uptake 0.73 0.36

Reaction with OH 0.10 0.14

CH3CN is a better tracer for biomass burning.

Atmospheric budgets of HCN and CH3CNGEOS-CHEM 2002

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Summary of results

1. 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].

2. 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].

3. 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].

4. 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].

5. 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].