Observations of an Atmospheric Chemical

Equator and its Implications for the

Tropical Warm Pool Region

Jacqueline F. Hamilton1, Grant Allen2, Nicola M. Watson1, James D. Lee1, Julie E. Saxton1, Alastair C. Lewis1, Geraint Vaughan2, Keith N. Bower2, Michael J. Flynn2, Jonathon Crosier2, Glenn D. Carver3, Neil R.P. Harris3,

Robert J. Parker4, John J. Remedios4, Nigel A.D. Richards5

1Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.2School of Earth, Atmospheric and Environmental Science, Sackville St Building, Sackville St, University of

Manchester, Manchester, M60 1QD, UK. 3Chemistry Department, University of Cambridge, Cambridge, CB2 1TN, UK.

4Earth Observation Science, Space Research Centre, Department of Physics & Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK.

5Institute for Atmospheric Science, School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK.

J. Geophys. Res., 113, D20313, doi:10.1029/2008JD009940, (2008).

Overview

• Flight tracks• Meteorology• Results

– Chemical characteristics – Trajectory analysis and biomass burning

• Comparison with Satellite and Model data

• Conclusions• Acknowledgements

• 2 measurement periods– Pre-monsoon (October – December 2005)– Monsoonal (January – March 2006)

• Monsoon period was composed of a number of different meteorological conditions– Active monsoon– Inactive monsoon– Break Period – with intense “Hector” storms over

Tiwi islands

Strong Westerly wind in Darwin, inhibited local convectionFlew north looking for the boundary between northern and southern hemispheric air.

Introduce the generic term “Chemical Equator” to describe a

defined boundary between tropospheric air of northern and

southern hemispheric origin

• Generally associated with the Inter-Tropical Convergence Zone (ITCZ)

• ITCZ is a low pressure region circling the globe where the trade winds associated with the Hadley circulation in NH and SH meet

• Characterised by rapid vertical uplift and heavy rainfall• Provide a meteorological barrier to cross equatorial flow

in the troposphere – exchange times around 6 months

Previous Studies of Chemical Equators

• There have been a number of studies of the characteristics on either side of the chemical equators associated with the ITCZ using aircraft

• Chemical Equators (CE) separates polluted NH from the pristine SH

• Differences in chemical signatures on each side dependant on location. Carbon Monoxide (CO) can be used as a tracer for transport of pollution– PEM-TROPICS B – CO 6-15 ppb higher N of ITCZ– INDOEX – average CO was 49 ppb at 5 º S and 175 ppb at 5 ºN

• Ship measurements during INDOEX showed factor of 3-4 increase in CO crossing the ITCZ

• Transition was found to be sharp – over the course of a day.

Chemical Equator • Difficult to sample across the ITCZ in aircraft as it is a

highly convective region• ITCZ is a complex system – can break down and

reform• A boundary between air with NH and SH chemical

signatures does not have to be associated with the ITCZ– Chemical Equator

• Chemical and aerosol data collected across a chemical equator using the Dornier during ACTIVE will be presented– High time resolution measurements of CO, O3 and aerosol

properties across the boundary– Lower-time resolution measurements of VOCs and CFCs give

averaged profiles on either side of the boundary

Flight Tracks• Flights part of ACTIVE – Dornier Survey

Flights– SD019 – 30th January 2006– SD022 – 3rd February 2006SD019 SD022

MeteorologySD019 30th Jan SD022 3rd Feb

MTSAT Infrared images 14:03 local

ECMWF Mean Sea level pressure and 10 m winds 15:30 local

Results – Time Series

CO O3

Aerosol

AMS

10

30

50

70

90

110

130

150

170

14:09:36 14:52:48 15:36:00 16:19:12 17:02:24 17:45:36 18:28:48

CO

(pp

b),

Alt/

20

(m

)

-2

8

18

28

38

48

58

68

Ozo

ne

(pp

b)

CO

Altitude/20

Ozone

10

30

50

70

90

110

130

150

170

14:38:24 15:21:36 16:04:48 16:48:00 17:31:12 18:14:24

CO

(ppb

), A

lt/20

(m)

-2

8

18

28

38

48

Ozone (ppb)

CO

Altitude/20

Ozone

0

50

100

150

200

250

300

14:38:24 15:21:36 16:04:48 16:48:00 17:31:12 18:14:24

Gri

mm

, A

SP

, F

SS

P*1

0 (

Pa

rtic

les

cm-3

)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

CP

C (P

article

s cm-3

)

GRIMM

ASP

FSSP*10

CPC

-1

0

1

2

3

4

5

6

7

8

14:38:24 15:21:36 16:04:48 16:48:00 17:31:12 18:14:24

Time Local (Darwin)

Mas

s L

oadi

ng (

mg

m-3

)

SULPHATEORGANICNITRATE

0

20

40

60

80

100

120

140

160

14:09:36 14:52:48 15:36:00 16:19:12 17:02:24 17:45:36 18:28:48G

rim

m,

AS

P,

FS

SP

*10

(P

art

icle

s c

m-3

)

0

500

1000

1500

2000

2500

3000

3500

4000

CP

C (P

artic

les c

m-3

)

GRIMMASPFSSP*10CPC

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

14:09:36 14:52:48 15:36:00 16:19:12 17:02:24 17:45:36 18:28:48

Time Local (Darwin)

Ma

ss L

oa

din

g (

g m

-3)

SULPHATE

ORGANIC

NITRATE

Time Local (Darwin) Time Local (Darwin)

Mas

s L

oad

ing

(g

m-3)

Mas

s L

oad

ing

(g

m-3)

Gri

mm

, A

SP

, F

SS

P*1

0 (P

arti

cles

cm

-3)

Gri

mm

, A

SP

, F

SS

P*1

0 (P

arti

cles

cm

-3)

CO

(p

pb

), A

lt/2

0 (m

)

CO

(p

pb

), A

lt/2

0 (m

)

Ozo

ne (p

pb

)

Ozo

ne (p

pb

)

CP

C (P

articles cm-3)

CP

C (P

articles cm-3)

SD019 SD022

CO and Ozone• CO is an ideal tracer for transport of pollution sources

– Photo-chemically produced via oxidation of CH4 and VOCs

– Direct emission from incomplete combustion sources (biomass/fossil)

• Ozone – by-product of VOC oxidation in presence of NOx.

• Coloured flight path by CO (40-150ppb). Transition at chemical equator is sharp (CO 40 to 165 ppb within 50 km)

ChemicalEquator

ChemicalEquator

SD019

SD022

Air Mass Origin

Coloured by CO40 ppb blue-160 ppb red

5 day back trajectory10 day back trajectory

Back trajectories calculated along the flight track using NOAA’s HYSPLIT model

CO and Ozone• Using trajectory analysis have separated the data according to

hemispheric origin (over the previous five days)

• Definite correlation between CO and O3 in NH air in SD022. Not as clear in SD019.

• Ratio of O3:CO in polluted NH air was 0.16.

• Similar to INDOEX – polluted air masses from India 0.14-0.16 • SE Asia biomass burning plumes – 0.12-0.2 Stehr et al., JGR-Atmos., 107, 19, 2002.

Kondo et al., JGR-Atmos, 109, 2004

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

0 20 40 60 80 100 120 140 160 180 200

CO (ppb)

Ozo

ne (p

pb)

Originated in NH

Originated in SH

y = 0.166x + 7.7424

R2 = 0.4509

y = -0.0965x + 24.742

R2 = 0.0285

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 20 40 60 80 100 120 140 160 180 200

CO (ppb)

Ozo

ne (

ppb)

Orginating in NH

Orginating in SH

Linear (Orginating in NH)

Linear (Orginating in SH)

SD019 SD022

Gas phase organics• Collected air samples onto absorbent tubes during flights and analysed using gas chromatography with time of flight

mass spectrometry. • 5 minute sample time – 15 tubes per flight.• Typical SH background concentrations determined using other flights under similar met conditions. (AD018 and

SD020/21 – Survey flights to Alice Springs) • Average VOC concentration determined for samples collected when air originated in NH.

• Elevated aromatic concentrations indicate a larger anthropogenic pollution source north of the chemical equator. Tracers for fossil fuel burning and transportation (i.e. evaporations from petrol stations)

• Also seen with other petroleum markers e.g. alkanesSH air (ppt) NH air (ppt) SH air (ppt) NH air (ppt)ethyl benzene 5.2 60.0 4-ethyl toluene 2.3 17.0m + p xylene 15.9 73.6 1,3,5-trimethyl benzene 3.3 28.5o -xylene 5.3 47.7 1,2,4-trimethyl benzene 5.9 37.5propyl benzene 1.6 30.5 1,2,3-trimethyl benzene 2.2 19.7isopropyl benzene 0.6 10.5 nonane 17.5 75.33-ethyltoluene 1.7 9.3

Biomass burning• The Moderate Resolution Imaging Spectroradiometer

(MODIS) onboard the Terra and Aqua Satellites can be used to detect thermal anomalies including fire occurrence

• Data obtained from http://landweb.nascom.nasa.gov/cgi-bin/browse/browse.cgi

Extensive fires burning in North Sumatara and SE Asia (Thailand)

Elevated pollutant levels are a result ofBIOMASS BURNING

ANDHIGHER BACKGROUND IN N. HEMISPHERE

Weekly mean upper troposphere MLS Cloud Filtered CO profile (ppbv) at approximately 215 mbar (29 January – 4 February 2006)

Evidence for uplift in convection?

Comparison to Satellite dataThe chemical equator can clearly been seen in the Western Pacific region in the TES data

The change in magnitude is not as great as in the in-situ measurements

- due to averaging over an 11-day time period to obtain sufficient satellite coverage

- averaging over the vertical column (approximately 5 km) and the higher tangent altitude of TES observations (mid-troposphere).

TES CO profile (ppbv) at approximately 600 mbar (25 January – 5 February 2006)

Modelling of Chemical equator• CO modelled using p-TOMCAT chemical transport

model, using ECMWF operational analyses.• Models chemistry, emissions, boundary layer mixing

and convective parameterisation were switched off– Advecting passive tracers only – features which

develop are due to forcing from analysed winds

Horizontal resolution (0.75 x 0.75 degrees)31 Vertical levels up to 10hPaHigh-resolution model initialised from lower resolution

run (that included all the model’s processes) at 1st January 2006.

Modelling of Chemical equatorHorizontal (830mb) Vertical (130 E)

SD01930/01/2006

SD02203/02/2006

The famous plot!!!

The Press!!

• Some of the weirder titles– 'Chemical equator' protects Antarctica's

clean air – There's A 'Chemical Equator' - And We're On

The Wrong Side Of It– Discovered: Nature Segregates Dirty, Rich

Nations From Clean, Poor World

Appeared in Nature, New Scientist, National Geographic, Discovery Channel, MSNBC, Fox

Conclusions and Implications• Evidence of a chemical equator was investigated using a

comprehensive combination of chemical and meteorological tools and techniques, over a broad range of spatial and temporal scales,  using the expertise of a large team of international scientists

• Transition was very sharp indicating inhibited inter-hemispheric mixing– CHEMICAL EQUATOR

• The effect of the CE is amplified by the landphoon to the south transporting very clean air from the Southern Ocean and extensive biomass burning in Sumatra and SE Asia to the north.

• In both flights, the air north of the chemical equator is highly polluted (CO, Ozone, aerosols and aromatic VOCs).

• Back trajectory analysis indicates that this polluted air has travelled to the chemical equator through a highly active convective region.

• Aircraft measurements indicate that deep convection in the TWP is an important mechanism (via rapid vertical transport) for injecting large quantities of highly polluted air to the upper troposphere.

• Comparison with satellite and model data indicates air lofted in the TWP may be highly polluted.

Acknowledgements• Thanks go to the rest of the ACTIVE team who took part,

particularly those whose data has been used

• Thanks to the pilots of the Dornier and staff at the Airborne Remote Sensing Facility (ARSF)

• Thanks to the collaborative projects SCOUT-O3 and TWP-ICE and the Australian Bureau of Meteorology. Satellite data and Met analysis are courtesy of TWP-ICE and BoM.

• Jonathan Jiang at JPL for MLS plots and the TES science team at JPL

• Fire count data was obtained from the World Fire Atlas project, the Data User Element of the European Space Agency, and plotted by Manasvi Panchal.