Organic Carbon in the Troposphere: How much is there and can we predict the future?
NCAR SeminarMay 19, 2008
Colette L. Heald* ([email protected])
*With acknowledgements to many people at the end!
TOPICS FOR TODAY
I. Total Observed Organic Carbon: Concept and Field Observations
II. Isoprene Emissions: Global Budgets and Predictions
I. Total Observed Organic Carbon: Concept and Field Observations
CARBON IN THE ATMOSPHERE
CO2 (820 PgC)
CH4 (4 PgC)
Organic Carbon (~10s TgC) +
Short-lived (reactive)
BUT important climate role : • direct aerosol radiative forcing• indirect via CCN• oxidant chemistry (O3, CH4, …)
CO(150 TgC)
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]
Good agreement between global model and IMPROVE observations for OC aerosol
concentrations in the US[Park et al., 2003]
OBS
MO
DE
L
GAS-PHASE CARBON MASS CLOSURE?2847 organic compounds identified in the atmosphere [Graedel et al., 1986]~104 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]
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
Note:Similar to defining
nitrogen family (NOy)
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]
MEAN DAYTIME TOOC OVER NORTH AMERICA
0
10
20
30
40
50
60
Mex
ico C
ity (T
0) /
8
Pittsb
urgh (P
AQS-S
)
Pittsb
urgh (P
AQS-W
)
R/V R
on Bro
wn (RHB)
Thompso
n Far
m (T
F)
Chebogue
Pt (CHB)
Trinid
ad H
ead (T
HD)
Mex
ico (M
EX)
NE US (W
P3)
NE Pac
ific
(IPX)
Azore
s (B
AE)
Fire P
lum
es (W
P3)
Org
anic
Car
bo
n [m
gC
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.
ORGANIC AEROSOL VS SULFATE OVER NORTH AMERICA
Mean POM ranges from < 1 to 24 μgm-3
OC aerosol equal/dominates sulfate at all sites, consistent with NH picture of Zhang et al. [2007]. No discernable trend with “age”.
0
5
10
15
20
25
30
35
Mex
ico C
ity (T
0)
Pittsb
urgh
(PAQ
S-S)
Pittsb
urgh
(PAQ
S-W)
R/V R
on Bro
wn (R
HB)
Thom
pson F
arm
(TF)
Chebogu
e Pt (
CHB)
Trinid
ad H
ead
(THD)
Mex
ico (M
EX)
NE US (W
P3)
NE Pac
ific
(IPX)
Azore
s (B
AE)
Fire P
lum
es (W
P3)
Aer
oso
l M
ass
Co
nce
ntr
atio
n [
mg
m-3
]
POM
SO4
SURFACE AIRCRAFT
VARIABILITY OF TOOC OVER NORTH AMERICA
Organic carbon concentrations span 2 orders of magnitude.Minimum of 2 μgCm-3 observed at any site.
OC aerosol never makes up more than 50% of TOOC.Clean marine sites similar (IPX, BAE)
Similar variability for platforms in the NE (RHB, TF, WP3)
WHAT CONTROLS THE VARIABILITY OF TOOC?
Gas-phase > particle-phase in ALL air masses, highest in NE US
CO is a good predictor for TOOC (46-86% of variability), but could be of biogenic or anthropogenic origin in US (see next slide)
Sulfate / Aerosol OC relationship driven by: sources, oxidants, loss?
BIOGENIC CONTROL ON TOOC? (SOA?)
Isoprene
HCHO
MVK/MACR
Isoprene + oxidation products predict some of TOOC
variability (but not OC aerosol)Methanol is best correlated tracer, with longest lifetime
(~7days), but not solely biogenic
Anthro sources
Conundrum: No strong indication of biogenic source of OC aerosol from observations,
but 14C indicates most OC aerosol is modern (=SOA?). Biogenic tracers too short-
lived? Need an anthropogenic “trigger” for aerosol formation?
QUESTIONS RAISED?
1. More routine total NMVOC measurements alongside speciated measurements, and semi-volatiles
2. More ambient sampling in diverse environments (tropics, Asia, polar)3. Time-resolved 14C observations (with aerosol and gas-phase measurements)
1. How much of TOC is accounted for in TOOC? (key missing compounds?)2. How representative are these observations of the atmosphere?
WHAT DO WE NEED?
[Heald et al., ACP, 2008]
TOPICS FOR TODAY
I. Total Observed Organic Carbon: Concept and Field Observations
II. Isoprene Emissions: Global Budgets and Predictions
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]
A MISSING FACTOR: ISOPRENE EMISSION INHIBITION BY CO2
Long-Term growth environment: gene adaptationDependent on ambient CO2
Short-term exposure: changes in metabolite pools and enzyme activityDependent on intercellular CO2
(varies with photosynthesis and stomatal resistance)
Mick Wilkinson and Russ Monson (UC Boulder) investigated these separately for 4 plant species and developed an empirical parameterization [Wilkinson et
al., submitted]
To what degree does this CO2 inhibition counteract predicted increases in isoprene (due to T and NPP)?
MODELING FRAMEWORK
Community Land Model (CLM3)Datasets: Lawrence and Chase [2007]
LAI (MODIS)Plant Functional Types
Soil moistureVegetation Temperature
BVOC Algorithms[Guenther et al., 1995; 2006]
Monterpenes: GEIAIsoprene: MEGAN
Community Atmospheric Model (CAM3)
ChemistryTransportRadiation
BVOC Emissions
VegetationMeteorology
RadiationPrecipitation
AnthropogenicEmissions,
GHG concentrations,SST
2100 (A1B): CO2 INHIBITION COMPENSATES FOR TEMPERATURE INCREASE
Future projected emissions drop from 696 TgC/yr to 479TgC/yr
See that ↑in T activity factor ~ compensated by ↓ in CO2 activity factor
Dotted=2000Solid=2100
CONCLUSION: ISOPRENE EMISSIONS PREDICTED TO REMAIN ~CONSTANT
Important implications for oxidative environment of the troposphere…
* With fixed vegetation
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]
IMPLICATIONS FOR THE PAST?
VOSTOK ICE CORE RECORD
While the balance between T and CO2 is critical to future predictions of isoprene, the large T fluctuations over the last 400 thousand year remain the
primary control on isoprene emission in the recent geological past.
Vostok data source: Petit et al. [1999]
ACKNOWLEDGEMENTS
Measurement Teams for ICARTT, PAQS, MILAGRO, IMPEX, ITCT-2K2:James D. Allan, Allison C. Aiken, Eric Apel, Elliot L. Atlas, Angela K. Baker, Timothy S. Bates, Andreas J. Beyersdorf, Donald R. Blake, Teresa Campos, Hugh Coe, John D. Crounse, Peter F. DeCarlo, Joost A. de Gouw, Edward J. Dunlea, Frank M. Flocke, Alan Fried, Paul Goldan, Robert J. Griffin, Scott C. Herndon, John S. Holloway, Rupert Holzinger, Jose L. Jimenez, Wolfgang Junkermann, William C. Kuster, Alastair C. Lewis, Simone Meinardi, Dylan B. Millet, Timothy Onasch, Andrea Polidori, Patricia K. Quinn, Daniel D. Riemer James M. Roberts, Dara Salcedo, Barkley Sive, Aaron L. Swanson, Robert Talbot, Carsten Warneke, Rodney J. Weber, Petter Weibring, Paul O. Wennberg, Douglas R. Worsnop, Ann E. Wittig, Renyi Zhang, Jun Zheng, Wengang Zheng
NSF, NOAA, NASA Funding for TOOC Measurements
NOAA Climate and Global Change Postdoctoral Fellowship
CO2 – Isoprene work: Mick Wilkinson, Russ Monson, Clement Alo, Guiling Wang, Alex Guenther
