Transcript Toward an integrated approach to tropospheric chemistry

Terrestrial emissions of
isoprene
Paul Palmer
Division of Engineering and Applied Sciences,
Harvard University
http://www.people.fas.harvard.edu/~ppalmer
Tropospheric O3 is an important
hv
climate forcing agent
O3
NO2
NO
OH
HO2
HC+OH  HCHO + products
NOx, HC, CO
Level of Scientific
Understanding
IPCC, 2001
Natural VOC emissions (50% isoprene) ~
CH4 emissions.
Isoprene emissions July 1996
GEIA
EPA BEIS2
7.1 Tg C
2.6 Tg C
MEGAN
[1012 atom C cm-2 s-1]
3.6 Tg C
Isoprene oxidation products (e.g. HCHO)
provide constraints on estimated emissions
Modeled HCHO [ppb]
GOME isoprene emissions (July 1996)
agree with surface measurements
0
12
ppb
r2 = 0.53
r2 = 0.65
Bias -3%
Bias -30%
GEIA
BEIS2
Observed HCHO [ppb]
Modeling the terrestrial biosphere
PAR – direct and
diffuse (GMAO)
Temperature:
Instantaneous (G95)
10-day avg (Petron ‘01)
Fixed base emission factors (Guenther 2004)
Altitude
Canopy model
(Guenther 1995)
LAI
Emission
MODIS/AVHRR
LAI
Emissions
April
Sep
Global 3-D Modeling Overview
•Driven by NASA GMAO met data
•2x2.5o resolution/30 vertical levels
•O3-NOx-VOC-aerosol chemistry
GEOS-CHEM
Global 3D CTM
PAR, T
Emissions
MODEL BIOSPHERE
MEGAN (isoprene)
Canopy model
Leaf age
LAI
Temperature
Base factors
GEIA
Monoterpenes
MBO
Acetone
Methanol
Monthly mean LAI (AVHRR/MODIS)
Isoprene Monoterpenes
MBO
May
Jun
Jul
Aug
VOC
emissions
during
2001
growing
season
Sep
[1012 atom C cm-2 s-1]
Cummulative HCHO Yield from isoprene oxidation (per C)
isoprene
0.55
at t progresses
further
0.4
0.40
0.50
0.5
HCHO YIELD PER C REACTED
Cumulative HCHO yield [per C]
HCHO production from biogenics
using the MCM
Y become closer
0.45
0.40
0.35
0.30
0.35
0.30
0.33
0.25
0.20
0.25
NOX = 0.1 PPB
0.20
NOX =1 PPB
0.15
0.15
0.10
GEOS-CHEM
0.10
NOX= 1 PPB
NOX= 100 PPT
 pinene (
pinene similar)
0.05
0.05
0.00
0.00
0
20
40
60
80
HOURS
TIME (HOURS)
100
120
140
0
2
4
6
8
10
12
14
16
18
20
22
DAYS
DAYS
Figure 18. Formation of HCHO from isoprene. Vertical lines denote midnight of each day
NOx = 1 ppb
NOx = 0.1 ppb
Use this analysis to
parameterise source of
HCHO from monoterpenes
Mike Pilling and Jenny Stanton, Leeds University
Global Ozone Monitoring Experiment
•Nadir-viewing SBUV instrument
•Pixel 320 x 40 km2
•10.30 am cross-equator time (globe in 3 days)
•O3, NO2, BrO, OClO, SO2, HCHO, H2O, cloud
•HCHO slant
columns fitted:
337-356nm
Isoprene
Biomass Burning
HCHO JULY 1997
•Fitting uncertainty
< continental
signals
GROWING SEASON 2001
GEOS-CHEM
GOME
GEOS-CHEM
GOME
May
Aug
Jun
Sep
Jul
HCHO column [1016 molec cm-2]
HCHO column signal from monoterpenes is
comparable to GOME column uncertainty
HCHO data over the Ozarks
SOS 1999
Aircraft data @ 350 m July 1999
Kansas
Missouri
Illinois
GOME
OZARKS
[ppb]
c/o Y-N. Lee, Brookhaven National Lab.
[1016 molec cm-2]
Relating HCHO Columns to VOC Emissions
hours
hours
HCHO
OH
h, OH
VOC
kHCHO HCHO
EVOC = _______________
kVOCYieldVOCHCHO
HCHO
Master Chemical Mechanism
Isoprene
-pinene
100 km
VOC source
propane
Distance downwind
Ultimate
Yield Y
(per C)
Approx.
Time to Y
isoprene
~0.5
2-3 hrs
 pinene
~0.3
3-4 days
 pinene
~0.25
3-4 days
MBO
~0.4
3-4 days
EVALUATE GOME DATA USING LONG-TERM
ISOPRENE FLUX DATA
PROPHET RESEARCH SITE (MI)
Maple, beech, birch, basswood, mixed aspen, bog conifers (lower, wet areas), and pine and
red oak (drier upland regions). Average height near 20 m. Overstory age of the hardwood
forest is approximately 75 years.
Wind direction associated with
largest [HCHO] in 1998 intensive
Long term in situ isoprene flux
measurements at PROPHET site during 2001
1212
-2-2
Isoprene
molec
s-1
]]
Isopreneflux
flux[10
[10
moleccm
cm
s-1
Measured
Measured (WSU)
(WSU)
MEGAN
MEGAN
GOME
GOME
HCHO column [1016 molec cm-2]
+/uncertainty
Y2K1 Day
Using observed isop flux:HCHO column regression
better agreement with GOME
May
June
July
August
September
1996
1997
1998
1999
2000
2001
HCHO column [1016 molec cm-2]
GOME HCHO Column [1016 molec cm-2]
Interannual variability of the seasonal cycle
Southeast US
32-38N; 265-280W
Days 2K1
GOME HCHO Column
[1016 molec cm-2]
In situ observations over Atlanta GA provide
some verification of large interannual
variability
Mean values
associated with
individual values
> 30 ppbC
r = 0.75
n=14
PAMS (EPA) Isoprene
Concentration (10-12 LT) [ppbC]
Lance
McCluney,
EPA
What is driving this variability?
2nd-order polynomial
fit to HCHO columns
r=0.9
Curve based on
greenhouse data
(Guenther)
Closing Remarks
• GOME HCHO data provide constraints on
natural VOC emissions
• Data consistent with seasonal and interannual
variability observed with in situ
measurements
• Improved understanding and quantification of
air quality and climate
• Just the beginning…need to relate modelobservation discrepancy to a better
understanding of the underlying processes