Transcript secondary organic aerosol

BIOGENIC AEROSOL:
SECONDARY ORGANIC AEROSOL (SOA)
PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)
THE IMPORTANCE OF ORGANIC AEROSOL
Sulfate Organics
[Zhang et al., 2007]
• Organic material contributes 20-50% of the total fine aerosol mass at continental mid-latitudes
[Saxena and Hildemann, 1996; Putaud et al., 2004] and as much as 90% in the tropical
forested areas [Andreae and Crutzen, 1997; Talbot et al., 1988; 1990; Artaxo et al., 1988; 1990;
Roberts et al., 2001]
ORGANIC CARBON AEROSOL
Secondary
Organic
Aerosol
Cloud
Processing
SemiVolatiles
Nucleation or
ReversibleCondensation
Primary
Organic
Aerosol
Oxidation
by OH, O3,
NO3
Monoterpenes
Aromatics
Isoprene
Sesquiterpenes
Direct
Emission
Fossil Fuel
Biomass
Burning
TOPICS FOR TODAY
1.
What are secondary organic aerosol?
2.
How do we model SOA? What are the estimated global
budgets?
3.
What are primary biological aerosol particles?
4.
What do we think drives these emissions?
5.
What are the challenges in understanding biogenic
organic aerosol budgets?
6.
How might SOA and PBAP be affected by climate
change?
SECONDARY ORGANIC AEROSOL PRODUCTION
VOC
Emissions
Oxidation
Reactions
(OH, O3,NO3)
Nucleation
(oxidation products)
Growth
Condensation
on pre-existing
aerosol
Over 500 reactions to describe the formation of SOA precursors, ozone, and other
photochemical pollutants [Griffin et al., 2002; Griffin et al., 2005; Chen and Griffin, 2005]
Nucleation
Burst
on 10/6/01
FINE PARTICLE
GROWTH
AT BLODGETT
FOREST
“Banana Plot”
4
D p (nm)
2
100
8
6
4
2
10
2 7 9 .0
2 7 9 .2
2 7 9 .4
2 7 9 .6
2 7 9 .8
2 8 0 .0
Day
-3
dN/dlog(D p ) (cm )
0
2000
4000
6000
8000
[Lunden et al., 2006]
GAS/PARTICLE PARTITIONING THEORY
VOC + oxidant  P1, P2, …Pn
M0 = pre-existing
OC aerosol
G1, G2, …Gn
A1,A2,...,An
Absorptive
Partitioning Theory
K om ,i 
Ai
RT
 o
Gi M 0 p i MWom i
[Pankow, 1994]
R=gas constant; T=temperature; p0i = vapour pressure, MWom=molecular weight of
aerosols; i=activity coefficient in organic phase
WHICH VOC’s ARE IMPORTANT SOA PRECURSORS?
Isoprene (C5H8)
Monoterpenes(C10H16)
Three factors:
1. Atmospheric Abundance
2. Chemical reactivity
3. The vapour pressure (or
volatility) of its products
Sesquiterpenes (C15H24)
Anthropogenic SOA-precursors =
aromatics (emissions are 10x smaller)
COMPARING SOA POTENTIALS
M 0
Y
HC
Terpenoids: Griffin et al., 1999:
Photo-oxidation: Y=1.6-84.5%
NO3 oxidation: Y=12.5-89.1%
O3 oxidation: Y=0-18.6%
Isoprene: Kroll et al., 2005
Photo-oxidation (OH): Y=0.9-3%
Aromatics: Ng et al., 2007
High NOx: Y=4-28%
Low NOx: Y=30-36%
EDGAR 1990 Emissions (Aromatics)
and GEIA (Isoprene/Monoterpenes)
Species
Global (Tg/yr)
Aromatics
Benzene
Toluene
Xylene
Other
21.7
5.8
6.7
4.5
4.7
SOA pot’l (15%)
3.2
Monoterpenes
130.6
SOA pot’l (10%)
13.1
Sesquiterpenes
?
SOA pot’l (75%)
?
Isoprene
341
SOA pot’l (3%)
10.2
TOPICS FOR TODAY
1.
What are secondary organic aerosol?
2.
How do we model SOA? What are the estimated
global budgets?
3.
What are primary biological aerosol particles?
4.
What do we think drives these emissions?
5.
What are the challenges in understanding biogenic
organic aerosol budgets?
6.
How might SOA and PBAP be affected by climate
change?
MODELING SOA: EXPLICIT CHEMISTRY
(APPROACH #1)
• Using mechanistic description of chemistry coupled to partitioning.
• Captures hundreds of species and reactions (e.g. Master Chemical Mechanism,
Leeds).
• Often reactions and rates have not been measured but are extrapolated from
known chemistry (by analogy).
Example: TORCH 2003 campaign in rural UK
To get this agreement:
1. Add 0.7 µg/m3 bkgd
2. Increase partitioning
coefficients by factor
of 500
[Johnson et al., 2006]
These authors previously found that they needed to increases
partitioning by a factor of 5-80 with the MCM to match aromatic SOA
formation at the EUPHORE chamber [Johnson et al., 2004; 2005].
MODELING SOA: 2-PRODUCT MODEL
(APPROACH #2)
• Unknown products, so
lump products into 1=high
volatility and 2=low
volatility
• Fit yields/partitioning
parameters (a’s K’s) from
smog chamber observations
•Used in most
global/regional models
SOA parameterization (reversible partitioning)
VOCi + OXIDANTj  ai,jP1i,j + ai,jP2i,j
Gi,j
Equilibrium (Komi,j)
 also f(POA)
Pi,j
Ai,j
Example: Global budget of biogenic SOA
SOA from monoterpenes, sesquiterpenes and OVOCs estimated to contribute
~15% of OA burden
[Chung and Seinfeld, 2002]
MODELING SOA: VOLATILITY BASIS SET
(APPROACH #3)
• Expand the 2-product model to consider many volatility “bins”
• Allows chemistry/physics to move organic matter along a continuum  physically
attractive
• Loss of chemical identity complicates estimates of “mean molecular weights” and
radiative forcing
Example: PMCAMx (summer 2001)
volatility
C* = saturation vapour pressure
[Donahue et al., 2005]
[Lane et al., 2008]
CURRENT ESTIMATES: GLOBAL BUDGETS OF SOA
Annual mean zonal distribution of SOA (2000)
[Heald et al., 2008]
GEOS-Chem model global annual budget
SOA Production
Tg yr-1
Isoprene
14.4
Monoterpenes
8.7
Sesquiterpenes
2.1
OVOC
1.6
Aromatics
3.5
TOTAL
30.3
[Henze et al., 2008]
POA Emission: 50-100 Tg yr-1
SOA ~ 25-50% of OA source in models
(mostly biogenic)
TOPICS FOR TODAY
1.
What are secondary organic aerosol?
2.
How do we model SOA? What are the estimated global
budgets?
3.
What are primary biological aerosol particles?
4.
What do we think drives these emissions?
5.
What are the challenges in understanding biogenic
organic aerosol budgets?
6.
How might SOA and PBAP be affected by climate
change?
PRIMARY BIOLOGICAL AEROSOL PARTICLES
(PBAP)
BACTERIA
VIRUSES
POLLEN
FUNGUS
PLANT
DEBRIS
ALGAE
Jaenicke [2005] suggests may be as large a source as dust/sea salt (1000s Tg/yr)
May act as CCN and IN [Diehl et al., 2001; Bauer et al., 2003; Christiner et al., 2008]
PBAP: PRESENT-THROUGHOUT THE YEAR, IN
URBAN AND RURAL LOCATIONS
Mainz, Germany (1990-1998)
Particles > 0.2 m, stained with
protein dye
No clear seasonality: multiple
PBAP sources
PBAP # fraction = 5-50%
Lake Baikal, Russia (1996-1997)
[Jaenicke, 2005]
PBAP: PARTICLES ACROSS THE SIZE RANGE
1.0E+1
3
dV /dlogd , µm /cm
3
200%
180%
160%
140%
120%
100%
80%
60%
40%
20%
0%
1.0E+0
Total
Cellular
1.0E-1
1.0E-2
1.0E-1
Fraction
1.0E+0
1.0E+1
1.0E+2
Diameter d , µm
May also make
important
contribution to
fine mode
aerosol
Dominates the
coarse mode
(pollens, debris,
etc)
From Andi Andreae (unpublished data)
MARINE PBAP
WIND
Sea-spray emission
of sea salt (and OC)
Surfactant Layer (with Organics)
Primary marine aerosol from “bubble
bursting mechanism” associated with sea
spray, correlated with periods of
biological activity.
Ocean
Mace Head, Ireland
Chlorophyll A
[O’Dowd et al., 2008]
TOPICS FOR TODAY
1.
What are secondary organic aerosol?
2.
How do we model SOA? What are the estimated global
budgets?
3.
What are primary biological aerosol particles?
4.
What do we think drives these emissions?
5.
What are the challenges in understanding biogenic
organic aerosol budgets?
6.
How might SOA and PBAP be affected by climate
change?
WHAT MIGHT DRIVE PBAP EMISSIONS/CONCENTRATIONS?
1. Wind
 Atmospheric release/dispersion
2. Temperature
 Can affect release (surface
bonding), proxy for growing
season?
3. Biological activity
 Stimulates source
4. Vegetation cover
 Source = vegetation, soil,
decaying matter
5. Humidity / wetness
6. Anthropogenic Activity
 Facilitates release (e.g. spores)
 Industrial/municipal facilities
e.g. spores/molds in old
buildings, sewage treatment
plants, textile mills
[Jones and Harrison, 2004]
TOPICS FOR TODAY
1.
What are secondary organic aerosol?
2.
How do we model SOA? What are the estimated global
budgets?
3.
What are primary biological aerosol particles?
4.
What do we think drives these emissions?
5.
What are the challenges in understanding biogenic
organic aerosol budgets?
6.
How might SOA and PBAP be affected by climate
change?
MEASURING OC IN THE ATMOSPHERE
Hamilton et al. [2004]: over 10 000 organic compounds detected in a single PM2.5
sample collected in London, England
CHALLENGE: To measure suite of compounds classified as organic carbon,
without artifacts from the gas phase
Ambient Air
Denuder to
remove gas-phase
organics
Quartz
Filter (#1)
Backup (#2)
(to capture OC
evaporated from
filter #1)
Thermal Optical
analysis to determine
OC Concentration
INTERPRETING ORGANIC AEROSOL MEASUREMENTS
CHALLENGE: once OA measured, can we separate POA and SOA?
Example from Pittsburg Air Quality Study [Cabada et al., 2004]
EC/OC ratio for primary
emissions are well-correlated
(triangles).
Deviations from the slope
are indicative of a secondary
OC source (squares).
Uncertainties:
• changing EC/OC emission ratios for sources
• mixing of air masses
EC=elemental carbon (direct emission only, primarily fossil fuel)
INTERPRETING ORGANIC AEROSOL MEASUREMENTS
AEROSOL MASS SPECTROMETER (AMS)
m/z 57: hydrocarbon
like organic aerosol
 POA
m/z 44: oxygenated
organic aerosol
 SOA
Reduce complexity of observed spectra to 2 signals:
~2/3 of OC is SOA
(in urban site!)
[Zhang et al., 2005]
SCALES OF MEASUREMENT
Escaped
Above-Canopy Flux
Measurements
O
+ O3
Oxidation Products
+ OH
Reacted
Oxidation Experiments
& In-Canopy Gradient
+ O3
+ O3
Emitted
Branch Enclosures:
Actual Emissions
Courtesy: Anita Lee (Berkeley, now EPA)
DISAGREEMENT BETWEEN MODELS AND OBSERVATIONS
1. Measurements are challenging, cannot distinguish POA & SOA, issues
such as collection efficiencies, artifacts can be important.
2. Models are simplified treatments (e.g. 2 product model)
3. Models are based on lab data (applicability to ambient conditions?)
[Volkamer et al., 2006]
TOPICS FOR TODAY
1.
What are secondary organic aerosol?
2.
How do we model SOA? What are the estimated global
budgets?
3.
What are primary biological aerosol particles?
4.
What do we think drives these emissions?
5.
What are the challenges in understanding biogenic
organic aerosol budgets?
6.
How might SOA and PBAP be affected by climate
change?
HOW MIGHT BIOGENIC OA CHANGE IN THE FUTURE?
Secondary
Organic
Aerosol
Cloud
Processing
SemiVolatiles
Nucleation or
ReversibleCondensation
Oxidation
by OH, O3,
NO3
Monoterpenes
Aromatics
Isoprene
Sesquiterpenes
Primary
Organic
Aerosol
T, Mo
Direct
Emission
Fossil Fuel
Biomass
Burning
PLUS: FEEDBACKS ON THE BIOSPHERE
Changing aerosol burden affects clouds/precip/chemical
deposition and radiation  changing SOA sources (BVOC)
Change in Emissions:
-4510 g m-2 h-1
to
5174 g m-2 h-1
Christine Wiedinmyer, NCAR