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
of Chemistry, University of York, Heslington, York, YO10 5DD, UK.
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.
2School
1Department
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 convection
Flew 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
– SD019 – 30th January 2006
– SD022 – 3rd February 2006
SD022
Meteorology
SD019 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
SD019
SD022
48
110
28
90
18
70
130
16:48:00
17:31:12
18:14:24
2000
GRIMM
1800
ASP
250
1600
1400
1200
150
1000
800
100
600
400
50
200
16:04:48
16:48:00
17:31:12
10
14:09:36
160
18:14:24
14:52:48
15:36:00
16:19:12
17:02:24
140
4
3
2
1
-3 -3
Mass
(g
Mass Loading
) )
mm
Loading (g
5
16:04:48
16:48:00
17:31:12
3000
80
2000
60
1500
40
1000
20
500
14:52:48
15:36:00
16:19:12
17:02:24
17:45:36
0
18:28:48
SULPHATE
ORGANIC
NITRATE
0.8
0.6
0.4
0.2
0
14:09:36
14:52:48
15:36:00
16:19:12
17:02:24
18:14:24
-0.4
Time Local (Darwin)
Time Local (Darwin)
3500
2500
-0.2
15:21:36
-2
18:28:48
4000
100
1
SULPHATE
ORGANIC
NITRATE
17:45:36
GR IM M
ASP
FS SP*10
C PC
120
0
14:09:36
1.2
0
15:21:36
6
Mass
m-3)
(gm-3)
MassLoading
Loading (mg
8
Time Local (Darwin)
Time Local (Darwin)
17:45:36
18:28:48
CP C (Particles cm -3)
CPC
200
0
14:38:24
-1
18
CPC (Particles cm-3)
FSSP*10
Grim m
, A SP,
FS SP*10
(Particlescm
cm-3-3)
Grimm,
)
ASP,
FSSP*10
(Particles
16:04:48
cm-3)
CPC
(Particles cm-3)
CPC(Particles
Grimm,
ASP,
FSSP*10(Particles
(Particles cm-3)
Grimm,
ASP,
FSSP*10
cm -3)
-2
15:21:36
7
AMS
28
70
30
10
0
14:38:24
8
38
90
8
30
Aerosol
48
110
50
50
14:38:24
300
58
(ppb)
Ozone
Ozone (ppb)
CO
(ppb), Alt/20 (m)
CO (ppb), Alt/20 (m)
130
CO
Altitude/20
Ozone
150
38
(ppb)
Ozone
Ozone (ppb)
CO
O3
CO
Altitude/20
Ozone
150
68
170
CO
(ppb), Alt/20 (m)
CO(ppb), Alt/20 (m)
170
•
•
•
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)
Chemical
Equator
Chemical
Equator
Air Mass Origin
Back trajectories calculated along the flight track using NOAA’s
HYSPLIT model
5 day back trajectory
10 day back trajectory
Coloured by CO
40 ppb blue-160 ppb red
SD019
SD022
CO and Ozone
• Using trajectory analysis have separated the data according to
hemispheric origin (over the previous five days)
SD019
45.00
SD022
60.00
Orginating in NH
Orginating in SH
Linear (Orginating in NH)
Linear (Orginating in SH)
40.00
50.00
Originated in NH
35.00
Originated in SH
40.00
Ozone (ppb)
Ozone (ppb)
30.00
25.00
20.00
15.00
30.00
y = -0.0965x + 24.742
2
R = 0.0285
y = 0.166x + 7.7424
R2 = 0.4509
20.00
10.00
10.00
5.00
0.00
0.00
0
20
40
60
80
100
120
140
160
180
200
CO (ppb)
0
20
40
60
80
100
120
140
160
180
200
CO (ppb)
• 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
•
•
•
•
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.
ethyl benzene
m + p xylene
o -xylene
propyl benzene
isopropyl benzene
3-ethyltoluene
•
•
SH air (ppt) NH air (ppt)
5.2
60.0
15.9
73.6
5.3
47.7
1.6
30.5
0.6
10.5
1.7
9.3
4-ethyl toluene
1,3,5-trimethyl benzene
1,2,4-trimethyl benzene
1,2,3-trimethyl benzene
nonane
SH air (ppt) NH air (ppt)
2.3
17.0
3.3
28.5
5.9
37.5
2.2
19.7
17.5
75.3
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. alkanes
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/cgibin/browse/browse.cgi
Extensive fires
burning in North
Sumatara and SE
Asia (Thailand)
Elevated pollutant levels are a result of
BIOMASS BURNING
AND
HIGHER BACKGROUND IN N. HEMISPHERE
Comparison to Satellite data
The 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 (midtroposphere).
Evidence for
uplift in
convection?
Weekly mean upper troposphere
MLS Cloud Filtered CO profile
(ppbv) at approximately 215
mbar (29 January – 4 February
2006)
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 10hPa
High-resolution model initialised from lower resolution run
(that included all the model’s processes) at 1st January
2006.
Modelling of Chemical equator
Horizontal (830mb)
Vertical (130 E)
SD019
30/01/2006
The famous plot!!!
SD022
03/02/2006
The Press!!
Appeared in Nature,
New Scientist,
National Geographic,
Discovery Channel,
MSNBC, Fox
• 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
•
•
•
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.