Transcript Transpacific transport of anthropogenic aerosols and

Secondary Organic Aerosols:
What we know and current CAM treatment
Colette L. Heald
([email protected])
Chemistry-Climate Working Group Meeting, CCSM
March 22, 2006
ORGANIC CARBON AEROSOL
*Numbers from IPCC [2001]
Reactive
Organic
Gases
Secondary Organic
Aerosol (SOA): 8-40 TgC/yr
Nucleation or Condensation
OC
Oxidation
by OH, O3, NO3
Monoterpenes
FF: 45-80 TgC/yr
BB: 10-30 TgC/yr
Aromatics
Direct
Emission
Fossil Fuel
BIOGENIC SOURCES
Biomass
Burning
ANTHROPOGENIC SOURCES
IN THE LAB: SMOG CHAMBER EXPERIMENTS
Teflon Chamber
VOC
eg. a-pinene
20-30°C
Oxidant (OH, O3, NO3)
High NOx
Yield 
M o
HC
SOA
formation
dry
seed particles
eg. (NH3)2SO4
Wall
loss
Yield 
Biogenic terpenes: yield 2-67%
[Griffin et al., 1999]
M o
HC
Issues:
1. High VOC concentrations
2. High oxidant and NOx concentrations
3. Relatively high (generally fixed) T
IN A MODEL: SOA PARAMETERIZATION
[Chung and Seinfeld, 2002]
Two Product Model [Odum et al., 1997]: ROGi + OXIDANTj  ai,jP1i,j + ai,jP2i,j
• once formed the semi-volatile reaction products (P) will partition b/w gas and
aerosol phase (as governed by the equilibrium partition coefficient (Kom)
[G]i , j ,k 
[ A]i , j ,k
Kom,i , j ,k M 0
[G] =product (gas) or SOG
[A] = product (aerosol) or SOA
Mo = concentration of total organic aerosol
• fitting parameters (a’s and K’s) from smog chamber data
• partition coefficients are temperature sensitive (use Clausius-Clapeyron eqn)
 H
K
(T )

  H= enthalpy of vaporization
om ,i , j , k
2
K om,i , j ,k (T1 )

T2
exp 
T1

i , j ,k
R
1 1
  
 T2 T1  
• at each time-step solve for equilibrium
ROG = 5 biogenic HC classes (terpenes and ORVOCs)
OXIDANT = OH, O3, NO3
 Carry both gas and aerosol phase products as tracers 
IN CAM: SIMPLIFIED 2-PRODUCT FORMULATION
[Lack et al., 2004]
For < 0.2 μg/m3 pre-existing OC: use bulk yield
For > 0.2 μg/m3: partition using two product model
• take parameters from smog chamber data
• ultimate yield calculated as:
 a i K om ,i 

Y  M 0  

i  1  K om ,i M 0 
• No temperature dependence on partitioning  corrected
• Add newly formed SOA to pre-existing
ROG = terpenes (C10H16), toluene and big alkanes (> heptane)
OXIDANTS = OH, O3, NO3
 Carry only lumped SOA product 
ADVANTAGE: one SINGLE tracer (for as many precursors as we want)
DISADVANTAGE: not representing equilibrium process
QUESTION: Is additional complexity warranted?
ACE-ASIA: OC AEROSOL MEASUREMENTS IN THE
FREE TROPOSPHERE
(ACE-Asia aircraft campaign conducted off of Japan during April/May 2001)
Seinfeld group
Huebert group
+
Russell group
Mean Observations
Mean Simulation (GEOS-Chem [Park et al., 2003])
Observations
High Levels of OC were observed in the FT during ACE-Asia by 2 independent
measurement techniques. We cannot simulate this OC with current models
[Heald et al., 2005].
UNDERESTIMATE OF OC AEROSOL DURING ICARTT
Observations
GEOS-Chem Simulation
OMC=organic molecular carbon (=1.4xOC)
WSOMC
WS=water soluble (10-80% of total OC, primarily SOA)
NOAA ITCT-2K4 flight tracks
SOA
OMC
(=POA+SOA)
Note: biomass burning plumes were removed
(R. Weber’s PILS instrument aboard)
OC aerosol underestimate observed
over North America as well
[Heald et al., in prep].
ISOPRENE AS A SOURCE OF SOA
Pandis et al., 1991
Smog
Chamber
Kroll et al., 2005
Edney et al., 2005
Smog
Chamber
Smog
Chamber
NO SOA observed
Yield = 0.9-3.0%
NO SOA observed
unless SO2 present
Claeys et al., 2004
Matsunaga et al., 2005
Lim et al., 2004
Ox VOC
Evap
Observed tetrols (ox
Observed ox products
Cloud processing of
product of isoprene) of isoprene in particulate Isoprene supported
Propose: acid-catalysed
phase.
by lab experiments
reaction w/ H2O2
Propose: polymerization
Isoprene is the second most abundant hydrocarbon emitted to the
atmosphere (~500 Tg/yr). Even with a modest yield this could be an
important source of SOA.
ORGANIC CARBON AEROSOL
*Numbers from IPCC [2001]
Reactive
Organic
Gases
Secondary Organic
Aerosol (SOA): 8-40 TgC/yr
Nucleation or Condensation
OC
Oxidation
by OH, O3, NO3
Monoterpenes
FF: 45-80 TgC/yr
BB: 10-30 TgC/yr
Aromatics
Direct
Emission
Fossil Fuel
BIOGENIC SOURCES
Biomass
Burning
ANTHROPOGENIC SOURCES
ORGANIC CARBON AEROSOL
Cloud
Processing
SOA: ?? TgC/yr
ROG
Nucleation or Condensation
OC
Heterogeneous Reactions
Oxidation
by OH, O3, NO3
Isoprene Monoterpenes
FF: 45-80 TgC/yr
BB: 10-30 TgC/yr
Aromatics
Direct
Emission
Fossil Fuel
BIOGENIC SOURCES
Biomass
Burning
ANTHROPOGENIC SOURCES
SOA FORMATION: PROCESSES TO CONSIDER
HC + oxidant +
1.
2.
3.
4.
5.
6.
7.
8.
Condensation
Multiple oxidation steps (explicit chemistry)
Isoprene as a source of SOA [Kroll et al., 2005; Henze et al., submitted]
Effect of NOx concentrations
 LAB
Temperature-dependence of formation
 LAB
Uptake on inorganic aerosols
 LAB
Polymerization reactions
 LAB
Heterogeneous reactions
 LAB
Cloud processing
Current plan for CAM:
1. Add isoprene as a source of SOA using 2-product framework
2. Put latest MEGAN biogenic emission model in CLM to drive CAM
3. Look at sensitivity of SOA formation to climate change