The current implementation of CO chemical production in the tagged CO simulation is outdated and inconsistent with full chemistry in a number of ways:• Production is limited to the surface layer• Methanol is inconsistent with full chem• Acetone uses outdated emissions and

yields• Short-lived VOCs are accounted for with

additional 10-20% scaling factor on emissions.

Further, the implementation does not allow tagging of the VOC contribution from different sources, a clear deficiency in source attribution for remote regions.

We suggest an updated implementation:1. Save P(CO) and L(CH4) from full chem2. Assume the CO yield from CH4 is 100%

(already assumed in tagged CO)3. Assume all other CO produced comes

from lumped NMVOCs4. Then P(CO)|CH4 = L(CH4)5. And P(CO)|NMVOC = P(CO) - P(CO)|CH46. Remove special scaling factors7. Run tagged CO with archived P(CO)8. Tag CO produced from NMVOCs by

location of production (like for Ox).Note: in the tropical lower troposphere, L(CH4) > total P(CO) - likely due to vertical transport of intermediate products. Extratropical CO impacts should be small.

A case study from February 2009 highlights two pathways for interhemispheric transport of Asian anthropogenic CO across the equator to the tropics (Darwin) and mid-latitudes (Wollongong).

• Asian pollution contributes to background concentrations at all times of year.• During the austral spring burning season, the area is heavily influenced by biomass

burning in Australia, South America, and Africa. The burning influence is minimal outside austral spring. South American burning was anomalously low in 2009, and a much larger influence from South America is seen in spring 2010 (not shown).

• The influence of different sources shows altitude dependence:• Asian pollution and Indonesian burning peak in the upper troposphere (>6 km)• South American and African biomass burning peaks in the mid-troposphere• Australian biomass burning is most important in the lower troposphere (< 4 km).

Acknowledgements: Darwin, Wollongong, and Lauder data are publicly available as part of the Network for the Detection of Atmospheric Composition Change (NDACC). This work was supported by a University of Wollongong Vice Chancellor’s postdoctoral fellowship.

References: Gloudemans, A.M.S., Krol, M.C., Meirink, J.F., de Laat, A.T.J., van

der Werf, G.R., Schrijver, H., van den Broek, M.M.P., Aben, I. (2006), Evidence for long-range transport of carbon monoxide in the Southern Hemisphere from SCIAMACHY observations, Geophys. Res. Lett., 33, L16897.

West, J.J., Naik, V., Horowitz, L.W., Fiore, A.M. (2009), Effect of regional precursor emission controls on long-range ozone transport - Part 1: Short-term changes in ozone air quality, Atmos. Chem. Phys., 9, 6077-6093.

SUMMARYWe identify the sources of carbon monoxide (CO) transported to Australasia (Australia & New Zealand) using GEOS-Chem tagged tracer simulations and ground-based remote-sensing data. We find that GEOS-Chem can accurately reproduce seasonal CO distributions at three Australasian sites ranging from the tropical north to the remote mid-latitudes.

Tagged tracer simulations indicate that the majority of observed CO is produced chemically from precursor emissions rather than emitted directly. This dominance points to the need for

updated treatment of CO production in the tagged CO simulation.

Focusing on direct emissions, we find contributions from a diverse set of sources, with biomass burning dominant during austral spring but not at other times of year. Fossil fuel pollution from China and Southeast Asia, predominantly transported via the upper troposphere, contributes to background CO in all seasons. During individual events, the Asian source can be responsible for up to 30% of CO in the tropics and 10-20% at mid-latitudes.

2. GEOS-Chem shows dominance of CO chemical production in remote regions

A few studies have addressed the potential influence of anthropogenic sources, but these have relied on models validated only at northern mid-latitudes and have not assessed the relative influence of anthropogenic versus biomass burning sources.

Modelled reduction in Australian ozone due to 10% reduction in regional NOx emissions, from West et al., 2009.

1. Motivation: Transport to Australasia

3. Direct emissions from diverse sources contribute to Australasian CO burdens

4. Cross-equator transport of CO from Asia to tropics and mid-latitudes

We use the GEOS-Chem v9-01-03 tagged CO simulation, with regional tags defined to identify potential contributions from different source regions in East and Southeast Asia.

Anthropogenic emissions are from EDGAR (globally), overwritten by Streets (Asia) and NPI (Australia). Biomass burning emissions are from GFED-3.

Initial simulations are for 2009, a year with no major Southern Hemisphere fires as well as available FTIR data.

Long-range transport of pollution to Australasia has previously been observed using satellite (MOPITT, SCIAMACHY) and ground-based data. The emphasis has been on massive, episodic biomass burning events, implying biomass burning is the dominant source of atmospheric pollution in the region. The potential influence of transported anthropogenic sources has largely been ignored.

Our motivating questions:• What are the relative roles of anthropogenic vs. biomass burning sources in driving

Australasian pollution on an ongoing (non-episodic) basis?• Are megacity fossil fuel emissions from East and Southeast Asia sufficiently large to

influence Australasia, despite the transport barrier at the equator?• How are emissions transported across the equator, and how do transport pathways vary

with climate and meteorology?

The figure compares simulated GEOS-Chem monthly mean CO total columns with observations from FTIR sensors at Darwin (tropical northern Australia: -12°S), Wollongong (urban southeast Australia: -34°S), and Lauder (remote New Zealand: -45°S).

The majority of CO at all Australasian sites is produced chemically from precursor emissions (CH4, VOCs). True attribution of pollution influence will require an updated treatment of chemical production in the tagged CO simulation (see box).

Direct emissions show similar contributions from anthropogenic and biomass burning sources at all sites. Biomass burning is large in the tropics during the burning season, and fossil fuel sources dominate in austral summer.

Sources and transport pathways of pollution in AustralasiaJenny A. Fisher1 (jennyf@uow.edu.au), Clare Paton-Walsh1, Rebecca Buchholz1, Dagmar Kubistin1, Guang Zeng2, John Robinson2, Lee T. Murray3

1University of Wollongong, Australia; 2National Institute of Water and Atmospheric Research, New Zealand; 3Harvard University, United States

SCIAMACHY CO, October 2004

Gloudemans et al., 2006

S.E. Asia

Africa

S. America

DarwinWollongong

Lauder

0.5 1.0 2.0 5.0 10.0 20.0 50.0 100.0 150.0 1011 molec/cm2/s

Darwin

0.5

1.0

1.5

2.0

2.5

3.0

Wollongong

0.5

1.0

1.5

2.0

2.5

3.0

Lauder

F A J A O D0.0

0.5

1.0

1.5

2.0

2.5

3.0

J M M J S N

CO

Col

umn

(101

8 mol

ec c

m-2

)

Chemical productionBiomass burningAnthropogenic

Obs. 2009Obs. 5-yr mean

Chemical production in tagged CO - a way forward?

Observed CO at Darwin, Feb. 2009

5 10 15 20 25Day in Month

1.2

1.4

1.6

1.8

CO

Col

umn

(101

8 mol

ec c

m-2

)

0

2

4

6

8

10

12

Altit

ude

[km

]

Australia-wide average profiles (direct emissions only)

0 5 10 15 20 25 30CO [ppbv]

0 5 10 15 20 25 30CO [ppbv]

Anthropogenic Australian Asian OtherBiomass Burning Australian South American African Other

Autumn (MAM)Spring (SON)

%CO at Darwin from Asian sources

5 10 15 20 25Day in 200902

0

2

4

6

8

10

12

Altit

ude

[km

]

0.

6.

12.

18.

24.

30. %

• Update simulations with new tagged chemical production (see box)• Use GEOS-Chem combined with satellite data (MLS + IASI) to identify meteorological

regimes that facilitate inter-hemispheric transport• Characterise seasonal & interannual variability in interhemispheric transport• Use results from Southern Hemisphere Model Intercomparison Project (UKCA, TM5,

CAM-chem, GEOS-Chem) to test robustness of results

Future Directions:

1. Frequent high-altitude transport from East Asia and Southeast Asia, followed by subsidence2. Occasional surface incursion of emissions from Indonesia and Southeast Asia, generally limited to the tropics

%CO at Wollongong from Asian sources

5 10 15 20 25Day in 200902

0

2

4

6

8

10

12

Altit

ude

[km

]

0.

5

10.

15.

20.

25.%

-20 -10 0 10 20 ppb

Change in [CO] at surface

-10 -5 0 5 10 ppb

Change in [CO] at 8 km-10

10ppb

-20

20