chemical and dynamical processes affecting the composition of the tropical pacific troposphere
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Chemical and Dynamical Processes Affecting the Composition of the Tropical Pacific Troposphere. Amanda Staudt Ph.D. Thesis Defense May 2001. The oxidizing capacity of the atmosphere. The ability of the atmosphere to remove many pollutants - PowerPoint PPT PresentationTRANSCRIPT
Chemical and Dynamical Processes Affecting the Composition of the
Tropical Pacific Troposphere
Amanda Staudt
Ph.D. Thesis Defense
May 2001
The oxidizing capacity of the atmosphere
• The ability of the atmosphere to remove many pollutants
• OH is the most important oxidant; formation of OH depends strongly on sunlight and water vapor:
O3 + hv O2 + O(1D)
O(1D) + H2O 2 OH
Maximum OH is found in the tropics
How do biomass burning, fossil fuel combustion, and lightning perturb the chemical composition of the tropical Pacific troposphere?
1. Large impact of biomass burning emissions on the chemical composition of the tropical Pacific troposphere
Major findings
3. Pathway for interhemispheric exchange above the eastern Pacific
4. NOx over the tropical Pacific is not in chemical steady state
2. European and Asian fossil fuel emissions have a large and comparable impact on CO in the lower troposphere over the North Pacific
Pacific Exploratory Missions to the Tropics
Species measured:•O3
•NO and NO2
•CO, CO2, and CH4
•OH and HO2
•PAN and HNO3
•peroxides
•CH2O•aerosols•many hydrocarbons
PEM-Tropics ASeptember 1996
PEM-Tropics BMarch-April 1999
Biomass fire counts from the Along Track Scanning Radiometer (ATSR)
PEM-Tropics BMarch-April 1999
North Pacific
High
South Pacific
High
North Pacific
High
South PacificHigh
ITCZ
PEM-Tropics ASeptember 1996
and SSM/I rainrates
outgoing longwave
OzoneColumns
Emissions
FSU Global Spectral Model• horizontal velocities• pressure, temperature, and relative humidity• optical depth• convective activity• precipitation
• 4° latitude x 5° longitude• 14 vertical layers• 1 hour timestep• 24 tracers
ECMWFassimilated
meteorologicalanalysis
radiation (OLR)
Harvard 3-D Model of
• detailed O3-NOx-hydrocarbon chemistry• tracer advection• convective transport• wet and dry deposition
Chemistry and Transport
Chemistry and TransportHarvard/FSU 3-D Model of
• Biomass burning pollution from South America and Africa during PEM-Tropics A
• Biomass burning and fossil fuel pollution from northern hemisphere continents during PEM-Tropics B
• Pathways for interhemispheric exchange in the upper troposphere during PEM-Tropics B
• Chemical cycling of NOx with HNO3 and PAN during PEM-Tropics A and B
Outline
• Biomass burning pollution from South America and Africa during PEM-Tropics A
• Biomass burning and fossil fuel pollution from northern hemisphere continents during PEM-Tropics B
• Pathways for interhemispheric exchange in the upper troposphere during PEM-Tropics B
• Chemical cycling of NOx with HNO3 and PAN during PEM-Tropics A and B
Outline
PEM-Tropics A biomass burning plumes
The strong correlation between O3 and CO demonstrates the pervasive influence of biomass
burning over the South Pacific.
Observations
Model
PEM-Tropics A observations from 0-30oS and 4-8 km
Southern
Hemisphere
Tropical
South Pacific
Fossil Fuel and Biofuel
14% 14%
Biomass Burning in South America
10% 13%
Biomass Burning in Africa
18% 14%
Biomass Burning in Australia and
Indonesia
5% 5%
CO Contributions during PEM-Tropics A
• Biomass burning pollution from South America and Africa during PEM-Tropics A
• Biomass burning and fossil fuel pollution from northern hemisphere continents during PEM-Tropics B
• Pathways for interhemispheric exchange in the upper troposphere during PEM-Tropics B
• Chemical cycling of NOx with HNO3 and PAN during PEM-Tropics A and B
Outline
PEM-Tropics B CO (ppb)
River of pollution
River of pollution
Interhemispherictransport
Interhemispherictransport
BiomassBurning
BiomassBurning
Observed
Simulated
Column CO (1017 molecules cm-2)
NorthAmericanfossil fuel
7%
Europeanfossil fuel
12%
Asianfossil fuel
15%
Biomass burning
27%
1. Large impact of biomass burning emissions on the chemical composition of the tropical Pacific troposphere
During September 1996, biomass burning in South America and Africa contributed 27% of simulated CO over the South Pacific
Biomass burning in southeast Asia and India contributed 27% of simulated CO over the North Pacific during March-April, 1999
Major findings
CO (ppb) observed during PEM-Tropics B
CO (ppb) at 400 m altitude
NorthAmericanfossil fuel
11%
Europeanfossil fuel
19%
Asianfossil fuel
19%
Biomass burning
17%
1. Large impact of biomass burning emissions on the chemical composition of the tropical Pacific troposphere
During September 1996, biomass burning in South America and Africa contributed 27% of simulated CO over the South Pacific
Biomass burning in southeast Asia and India contributed 27% of simulated CO over the North Pacific during March-April, 1999
Major findings
2. European and Asian fossil fuel emissions have a large and comparable impact on CO in the lower troposphere over the North Pacific
• Biomass burning pollution from South America and Africa during PEM-Tropics A
• Biomass burning and fossil fuel pollution from northern hemisphere continents during PEM-Tropics B
• Pathways for interhemispheric exchange in the upper troposphere during PEM-Tropics B
• Chemical cycling of NOx with HNO3 and PAN during PEM-Tropics A and B
Outline
Transport of CO in the upper troposphere (8-12 km altitude)
Longitudinal gradients for 0-20oS and 8-12 km altitude
Convectiveoutflow
Convectiveoutflow
Westerlyduct
32%25% 18%
Simulated transport fluxes of European fossil fuel CO during PEM-Tropics B
10-13.5 km altitude
Westerly duct = a region of upper tropospheric westerlies
Zonal winds (m/s) in the upper troposphere during PEM-Tropics B
Easterlies Easterlies
Westerlies
Westerlies
Westerly duct
The westerly duct is strongest during:• northern hemisphere winter and spring• La Nina conditions
1. Large impact of biomass burning emissions on the chemical composition of the tropical Pacific troposphere
During September 1996, biomass burning in South America and Africa contributed 27% of simulated CO over the South Pacific
Biomass burning in southeast Asia and India contributed 27% of simulated CO over the North Pacific during March-April, 1999
Major findings
3. Pathway for interhemispheric exchange above the eastern Pacific
The westerly duct was the dominant conduit for northern hemispheric air into the southern hemisphere during March-April, 1999
2. European and Asian fossil fuel emissions have a large and comparable impact on CO in the lower troposphere over the North Pacific
• Biomass burning pollution from South America and Africa during PEM-Tropics A
• Biomass burning and fossil fuel pollution from northern hemisphere continents during PEM-Tropics B
• Pathways for interhemispheric exchange in the upper troposphere during PEM-Tropics B
• Chemical cycling of NOx with HNO3 and PAN during PEM-Tropics A and B
Outline
NO NO2
PAN
HNO3
• deposition
• scavenging
• photolysis
• thermal decomposition
• NO2+CH3COO2+M
• NO2+OH+M
• N2O5+H2O
• photolysis
• HNO3+OH
Primary sources:• lightning• biomass burning• fossil fuel• soils• biofuel burning• aircraft
NOx budget
NO NO2
PAN
HNO3
• deposition
• scavenging
• photolysis
• thermal decomposition
• NO2+CH3COO2+M
• NO2 +OH+M
• N2O5+H2O
• photolysis
• HNO3+OH
Primary sources:• lightning• biomass burning• fossil fuel• soils• biofuel burning• aircraft
NOx budget
Loss of NOx
Production of NOx
1Chemical steady state:
LNOx/PNOx
during PEM-Tropics A
Harvard/FSU ModelAverage
LNOx/PNOx=1.6
Observed Average
LNOx/PNOx=1.9-
2.4
6-12 km, 10-30oS
PEM-Tropics B
Sensitivity simulations:
• Source of NOx from lightning increased by 50%
• Convective scavenging of HNO3 by ice turned off
• Acetone concentrations set to a minimum of 400 ppt
• Acetaldehyde concentrations set to a minimum of 80 ppt
No scavengingby ice
Standardsimulation
Fixedacetone
Fixedacetaldehyde
NOx chemical budget during PEM-Tropics B
1. Large impact of biomass burning emissions on the chemical composition of the tropical Pacific troposphere
During September 1996, biomass burning in South America and Africa contributed 27% of simulated CO over the South Pacific
Biomass burning in southeast Asia and India contributed 27% of simulated CO over the North Pacific during March-April, 1999
Major findings
3. Pathway for interhemispheric exchange above the eastern Pacific
The westerly duct was the dominant conduit for northern hemispheric air into the southern hemisphere during March-April, 1999
4. NOx over the tropical Pacific is not in chemical steady state
Emissions of NOx from lightning maintain a chemical imbalance in the tropical upper troposphere
New observations of elevated carbonyl concentrations over the Pacific raise questions about PAN chemistry
Scavenging of HNO3 can also cause a chemical imbalance
2. European and Asian fossil fuel emissions have a large and comparable impact on CO in the lower troposphere over the North Pacific