Organic Carbon in the Troposphere:Mysteries and Challenges
Michigan TechOctober 19, 2009
Colette L. Heald*
*with acknowledgements to many people at the end
CARBON IN THE ATMOSPHERE
Organic Carbon
+
Organic Carbon is a small part of the carbon pie: but it is the MOST reactive part (so LARGE fluxes) and the part that we know the LEAST about .
Is it important to understand this better?
CONNECTION TO BIG RESEARCH TOPICS IN ATMOSPHERIC SCIENCE…A MOTIVATION TO GET IT RIGHT!
AIR QUALITY / HEALTH
Clear DayVISIBILITY BIOSPHERE-ATMOSPHERE
CLIMATE
DISTURBANCE:Fires, beetles,
land use change
EMISSIONS:Particles, Organics, NOx, …
+ oxidation
O3
↓ OH = ↑ CH4 lifetime
+ FEEDBACKS FROM CLIMATE CHANGE
(moisture, precipitation, T, hv)
?
PRIMARY OA
SECONDARY OA +
oxidation
ECONOMICS, POPULATION, ENERGY USE
?
PARTS OF THE PUZZLE…
1. The budget: how much organic carbon is there in the atmosphere and in what phase?
2. An example of challenges in the gas-phase: ISOPRENE EmissionsChemistry
3. Challenges on the particle side:Missing primary biological sourcesHow to simplify all that complex chemistry….? Is there any
hope?
GAS-PHASE CARBON MASS CLOSURE?2847 organic compounds identified in the atmosphere [Graedel et al., 1986]>105 compounds estimated to be present [Goldstein and Galbally, 2006]30-100 compounds quantified in typical measurement campaigns
[Roberts et al., 1998]
Chebogue Pt, 1993 (NARE)
ΣC2-C7 agree with total measured within measurement uncertainty
Total T=Speciated S
T/S ~ 1+
UCLA, 1999-2000
WINTER
SUMMER
T/S ~ 1+
T/S =1.4-2.2
Suggest that 20-45% NMOC unmeasured in photochemically aged airmasses
[Chung et al., 2003]
RECONCILING THE ORGANIC AEROSOL BUDGETSOA measured/modeled = 4-100!
[Volkamer et al., 2006]
Global measurements (surface 0.5-32 μgm-3)[Zhang et al., 2007]
PHASES OF ORGANIC CARBON GENERALLY CONSIDERED SEPARATELY OR ‘ONE-WAY’
Oxidation &Condensation
POA
SOA
Deposition Deposition
Oxidation toCO/CO2
CONSIDER TOTAL ORGANIC CARBON (TOC)
Oxidation &Condensation
Deposition
Oxidation toCO/CO2
Oxidation &Re-volatization
TOC
SEMI-VOLATILES
CH4 Oxidation
FIELD SITES AND CAMPAIGNS
Eleven datasets upwind/over/downwind of North America with simultaneous observations of gas phase and particle phase OC.
(Over 130 organic compounds measured)
TOC = Σgas-phase OC + aerosol-phase OCTOOC = Total Observed Organic Carbon [μgCm-3 @ STP]
[Heald et al., ACP, 2008]
MEAN DAYTIME TOOC OVER NORTH AMERICA
0
10
20
30
40
50
60
Mexico
City (T
0) / 8
Pittsburg
h (PAQS-S
)
Pittsburg
h (PAQS-W
)
R/V Ron B
rown (RHB)
Thompso
n Farm (T
F)
Chebogue P
t (CHB)
Trinidad
Hea
d (THD)
Mexico
(MEX)
NE US (W
P3)
NE Pacific
(IPX)
Azores (
BAE)
Fire P
lumes (W
P3)
Org
anic
Car
bon
[mgC
m-3
] OC aerosol ethanepropane butaneacetone methanolethanol acetic acidformic acid acetaldehydeformaldehyde monoterpenesisoprene MVK+MACRaromatics PANssum(halogens) other
SURFACE AIRCRAFT
Increasing “age”
Mean TOOC ranges from 4.0 μgCm-3 (Trinidad Head, cleanest) to 456 μgCm-3 (Mexico City, polluted) and generally decreases with age.
Aerosol makes up 3-17% of TOOC.
PARTS OF THE PUZZLE…
1. The budget: how much organic carbon is there in the atmosphere and in what phase?
2. An example of challenges in the gas-phase: ISOPRENE EmissionsChemistry
3. Challenges on the particle side:Missing primary biological sourcesHow to simplify all that complex chemistry….? Is there any
hope?
ISOPRENE: CONTROLLING AIR QUALITY AND CLIMATE
C5 H8: Reactive hydrocarbon emitted from plants (primarily broadleaf trees)
Annual global emissions ~ equivalent to methane emissions
+ OH
O3
Depletes OH = ↑ CH4 lifetime
IPCC, 2007Beijing
CLIMATE
AIR QUALITY
METEOROLOGICAL AND PHENOLOGICAL VARIABLES CONTROLLING ISOPRENE EMISSION
LIGHTDiffuse and direct radiationInstantaneous and accumulated (24 hrs and 10 days)
TEMPERATURE (Leaf-level)instantaneous and accumulated (24 hrs, 10 days)
TPAR
L
T
[Guenther et al., 2006]SOIL MOISTURE suppressed under drought
AMOUNT OF VEGETATION Leaf area index (LAI)
Month
LAISUMMER
LEAF AGEMax emission = mature Zero emission = new
ISOPRENE IN THE FUTURE
Isoprene emissions projected to increase substantially due to warmer climate and increasing vegetation density.
LARGE impact on oxidant chemistry and climate
2000 2100
NPP ↑ Temperature↑
Surface O3 ↑ 10-30 ppb [Sanderson et al., 2003]
Methane lifetime increases[Shindell et al., 2007] SOA burden ↑ > 20%
[Heald et al., 2008]
CO2 INHIBITION COMPENSATES FOR PREDICTED TEMPERATURE-DRIVEN INCREASE IN ISOPRENE EMISSION
CONCLUSION: Isoprene emission predicted to remain ~constantImportant implications for oxidative environment of the troposphere…
* With fixed vegetation
508 523
696
479E isop
(TgC
yr-1
)2000 2100 (A1B)
MEGANMEGAN with CO2 inhibition
Global Model: NCAR CAM3-CLM3 (2x2.5)
Empirical parameterization from plant studies
[Wilkinson et al., 2009]
UNLESS…CO2 FERTILIZATION IS STRONG
CLM DGVM projects a 3x increase in LAI associated with
NPP and a northward expansion of vegetation.
[Alo and Wang, 2008]
Isoprene emissions more than double! (1242 TgCyr-1)
BUT, recent work suggests that NPP increases may be
overestimated by 74% when neglecting the role of nutrient
limitation [Thornton et al., 2007]
[Heald et al., GCB, 2009]
AND I HAVEN’T EVEN MENTIONED THESE…
Pictures courtesy: Nick Hewitt, Christine Wiedinmyer
Deforestation in Rondonia Boreal wildfiresPine beetle kill in the Rocky Mountains Palm Plantations in Malaysia
AMAZE field campaign
Obs (NCAR)GEOS-Chem
High isoprene concentrations titrates OH in low NOx regions (esp Amazon)
Leads to a factor 3-10 overestimate of observed
isoprene!
up to 29 ppb in Amazon
ONCE IN THE ATMOSPHERE, CHEMISTRY OF ISOPRENE NOT WELL UNDERSTOOD…
Model simulation (GEOS-Chem) with “standard” chemistry
PARTS OF THE PUZZLE…
1. The budget: how much organic carbon is there in the atmosphere and in what phase?
2. An example of challenges in the gas-phase: ISOPRENE EmissionsChemistry
3. Challenges on the particle side:Missing primary biological sourcesHow to simplify all that complex chemistry….? Is there any
hope?
PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)
POLLEN
BACTERIA VIRUSES
FUNGUS
ALGAEPLANTDEBRIS
Jaenicke [2005] suggests may be as large a source as dust/sea salt (1000s Tg/yr)Elbert et al. [2007] suggest emission of fungal spores ~ 50 Tg/yr
CURRENT SOURCE ESTIMATES FOR ORGANIC AEROSOL (Tg/yr)
WITHOUT PBAP WITH PBAP?
PBAP estimates ~1000 Tg/yr would swamp all other sources of organic aerosol. Fungal spores emissions equivalent to biomass burning?
Budget #’s from GEOS-Chem [Park et al., 2003; Henze et al., 2008]
PBAP ACROSS THE SIZE RANGE?
1.0E-2
1.0E-1
1.0E+0
1.0E+1
1.0E-1 1.0E+0 1.0E+1 1.0E+2
Diameter d , µm
dV/d
logd
, µm
3 /cm
3
0%20%40%60%80%100%120%140%160%180%200%
Total
Cellular
Fraction
From Andi Andreae (unpublished data)
Dominates the coarse mode (pollens, debris…)
May also make important contribution to fine mode
aerosol
PM2.5
USING OBSERVATIONS OF MANNITOL TO OPTIMIZE A SIMULATION OF FUNGAL SPORES
I. Identify tracer to test simulation: Mannitol is a unique tracer for fungal spores [Bauer et al., 2008; Elbert et al., 2007]
1 pg mannitol = 38 pg OM*
II. First-guess: constant emissions from Elbert et al. [2007], with 20% in fine mode
III. Optimize emissions: Test meteorological drivers to reproduce observed variability
Potential meteorological/phenological drivers [Jones and Harrison, 2004]: Temperature, radiation, wind speeds,surface wetness, precipitation, leaf area index (LAI), RH, water vapour concentrations and boundary layer depths
BEST drivers are LAI and water vapour concentrations.
CAUTION: not necessarily causal!
WHERE ARE FUNGAL SPORES AN IMPORTANT SOURCE OF ORGANIC AEROSOL?
Generally contribute ~10% to fine mode surface OA, but > 30% in tropics
WHEN ARE FUNGAL SPORES AN IMPORTANT SOURCE OF ORGANIC AEROSOL?
Pronounced seasonality in extratropics (corresponding to
vegetation cover), peaking in late-summer/fall as in measurements.
Taiwan
Hyytiala
[Sousa et al., 2008]
[Ho et al., 2005]
unpublished data, Hanna Manninen
Porto, Portugal
GEOS-Chem simulation
PBAP CONCLUSIONS
Fungal spores make a modest, but regionally important contribution to organic carbon aerosol budget. More observations needed to test…
What about other PBAP types?
FINE OA SOURCES COARSE OA SOURCE
(Tg yr-1) (Tg yr-1)
[Heald and Spracklen, GRL, 2009]
PARTS OF THE PUZZLE…
1. The budget: how much organic carbon is there in the atmosphere and in what phase?
2. An example of challenges in the gas-phase: ISOPRENE EmissionsChemistry
3. Challenges on the particle side:Missing primary biological sourcesHow to simplify all that complex chemistry….? Is there any
hope?
HOW DOES AEROSOL COMPOSITION CHANGE?Organic aerosol consists of MULTITUDES of species, and can be produced in MANY ways.
Once in the atmosphere, OA continues to evolve (oxidation = functionalization/fragmentation)Typically less than 20% of the mass of OA can be speciated [Williams et al., 2007]
This looks HOPELESS!Can we learn anything from looking at the bulk composition?
Van Krevelen diagram
AEROSOL “AGING” = CONSISTENT COMPOSITION CHANGES
Surprisingly, despite complexity, aerosol composition changes during aging looks like carboxylation!
EXAMPLES FROM TWO FIELD CAMPAIGNS…
[Heald, Kroll et al., in prep]
Tight correlation on the “carboxylation line” for OA observed at Riverside, CA
Aircraft observations around Mexico City coloured by photochemical clock shows how composition moves down the line with “aging” Hope for models?
DISTURBANCE:Fires, beetles,
land use change
EMISSIONS:Particles, Organics, NOx, …
+ oxidation
O3
↓ OH = ↑ CH4 lifetime
PRIMARY OA
SECONDARY OA +
oxidation
ECONOMICS, POPULATION, ENERGY USE
?
CONCLUSIONS• SIGNIFICANT challenges in measuring and modeling organic carbon in the atmosphere• Fundamentally incomplete picture of the budget• Rapid developments to be anticipated!
TOOC work:Measurement Teams for ICARTT, PAQS, MILAGRO, IMPEX, ITCT-2K2:James Allan, Allison Aiken, Eric Apel, Elliot Atlas, Angela Baker, Timothy Bates, Andreas Beyersdorf, Donald Blake, Teresa Campos, Hugh Coe, John Crounse, Pete DeCarlo, Joost de Gouw, Ed Dunlea, Frank Flocke, Alan Fried, Paul Goldan, Allan Goldstein, Rob Griffin, Scott Herndon, John S. Holloway, Rupert Holzinger, Jose Jimenez, Wolfgang Junkermann, William Kuster, Alastair C. Lewis, Simone Meinardi, Dylan Millet, Tim Onasch, Andrea Polidori, Patricia Quinn, Daniel D. Riemer James Roberts, Dara Salcedo, Barkley Sive, Aaron Swanson, Robert Talbot, Carsten Warneke, Rodney Weber, Petter Weibring, Paul Wennberg, Douglas Worsnop, Ann Wittig, Renyi Zhang, Jun Zheng, Wengang Zheng
Isoprene & CO2 work:Mick Wilkinson, Russ Monson, Clement Alo, Guiling Wang, Alex Guenther
Fungal spore work:Dominick Spracklen
Aerosol Aging work:Jesse Kroll, Jose Jimenez, Ken Docherty, Pete DeCarlo, Allison Aiken
ACKNOWLEDGEMENTS