The Influence of Aerosols on Plant Growth

Mike Bergin1,2

1 School of Civil and Environmental Engineering2 School of Earth and Atmospheric SciencesGeorgia Institute of Technology

http:\\www.ce.gatech.edu\~mhbergin

GeorgiaInstituteof TechnologyHonolulu, May 2002

How Might Aerosols Influence Plants?

• Directly changing the quantity and quality of photosynthetically active radiation (PAR) reaching the surface

• Modifying climate•Temperature•Precipitation•Indirectly modifying surface PAR

• Damaging plants by acidic deposition

• Increasing growth by deposition of nutrients

Possible Consequences?

• Decrease in Crop Production

• Modification of Carbon Cycle

Very Basic Chemistry of Photosynthesis

H2O + CO2 + hν >> CH2O + O2

* Also need nutrients such as N, P

Absorption of Solar Energy by Plants

Noble, 1999

CO2 Uptake vs. PAR

0

10

20

30

40

50

0 400 800 1200 1600 2000

PAR [µmol/m2s]

CO

2 U

pta

ke

[µ

mo

lCO

2/m

2s]

C3 plantC4 plant

Regional Nature of Aerosols in China

Chameides et al., 1999

Aerosol Spatial Distribution in the U.S.

I0

Is

Ia,anthro

Is/ I0=e-(τa− τg)

Top of the atmosphere (toa)

Surface

∆Ftoa = Ia,anthro - Ia,back

= f (τa ,ω0, β)where:τa = Aerosol Optical Depthω0 = Single Scattering

Albedo (σsp/σextp)β = UpscatterFraction

INFLUENCE OF AEROSOLS ON SHORTWAVE RADIATION DURING CLEAR-SKY CONDITIONS: KEY PARAMETERS

0

5

10

15

20

25

30

35

40

45

50

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3

τ500

Freq

uenc

y

0

100

200

300

400

500

600

Linan, China Atlanta

Background U.S.

Aerosol Optical Depth at a Few Locations

• τ500 ~ factor of 2-3 greater than polluted region of U.S.

Linan, China

Relationship Between Aerosol Optical Depth and PAR During Clear-Sky Conditions

200

250

300

350

400

450

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

τ500 / µ

PA

R (W

m-2

) / µ

r2 = 0.82Slope = -80 +/- 8 W m-2

• Aerosols can decrease PAR by ~ 20 - 30% during clear conditions in China• Estimated 24-hr average ∆FTOA is ~ -11 W m-2

Sensitivity of Crop Model Rice and Wheat Yield to Surface Irradiance

• Crop Growth = f (PAR, nutrients, water, T, RH)

Chameides et al., 1999

Can the Quality of Solar Radiation Reaching the Surface Influence Plant Growth?

NE

E o

f CO

2(µ

mol

m-2

s-1)

Clearness Index

Gu et al., 1999

1.0

0.8

0.6

0.4

0.2

0.0

diff

use

frac

tion

1.00.80.60.40.20.0aerosol optical depth

250

200

150

100

50

0

PA

R (W

/m2)

clear skies diffuse fractionclear skies PARcloudy skies diff. fractioncloudy skies PAR

Relationship Between Aerosols and Diffuse PAR

Can the Quality of Solar Radiation Reaching the Surface Influence Plant Growth?

sunlit leaves

shaded leaves

direct PAR

diffuse PAR

CO Uptake vs. PAR2

PAR

CO

U

ptak

e2

CO Uptake vs. PAR2

PARCO

U

ptak

e2

Model Estimation of the Influence of Diffuse Radiation on NPP ?

25

30

35

40

45

50

55

60

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Aerosol Optical Depth

24-h

ou

r N

PP

(gC

O2/

m2 /d

ay)

cloudlesscod = 2cod = 10aggregate

Cohan et al., 2002

The Estimated Influence of Aerosols on Crop Production Over a Growing Season: India Rice

perc

ent c

hang

e in

yie

ld

AOD

Greenwald et al., 2002

Influence of Water Stress on Grain Yield During 1998

• Russian wheat yield down ~40% due to drought• World grain yield down ~4%

Cost of 10% Reduction in Rice Yield in China and India (Economics Slide)

• In 1999/2000 India and China combined produced ~333 million metric tons of rice

• At a price of $200 / ton a 10% reduction in this value costs about $7 billion

• The FY2000 budget for NSF was $3.6 billion

The influence of Mt. Pinatubo on Global Aerosol Optical Depth

E. Dutton, pers. comm.

How Did Pinatubo Influence Surface Radiation and Carbon Uptake ?

•Surface irradiance decrease of ~4%; ~10% decrease in direct irradiance; ~40% increase in diffuse irradiance

•Global cooling of ~0.2 deg C

•Significant increase in terrestrial carbon uptake (~2 Gt C), particularly in northern hemisphere

• Increasing plant growth due to precipitation changes?

• Decrease in soil respiration?• Increase in the diffuse radiation fraction

enhancing plant growth?

Influence of Aerosol Dry Deposition on PAR Available to a Plant for Photosynthesis

leaf

Io

Il

( ) tßscatEabsELAI

pCdV(t)PAREX +

=

Where:

EXPAR(t) = Fractional reduction in incident PARVd = Aerosol dry deposition velocityCp = WIA concentration LAI = Leaf area indexEabs = Mass absorption efficiency Escat = Mass scattering efficiency

Bergin et al., 2001

Mass concentration (µgm-3)Mean Std. Dev

Mean % contribution toPM2.5 mass

PM2.5 102.4 52.3OrganicCompounds

50.4 27.4 48

Sulfate 24.2 12.8 23Ammonium 9.8 5.7 9Nitrate 8.8 7.7 8ElementalCarbon (EC)

5.4 2.0 5

Sodium 3.4 1.3 3Other 3.8 5.3 4Water InsolubleAerosol (WIA)

34.0 14.0 33

Extinction Efficiency (m2 g-1)Mean Std. Dev.

Eabs

Escat

0.86

4.0

0.70

0.4

AEROSOL PROPERTIES IN IN LINAN, CHINADURING NOV.-DEC., 1999

Deposition of Aerosol Particles to Leafs

Aerosol Particles Deposited on Leaves

• Results suggest as much as a 30% reduction in PAR available to plants over a growing season due to extinction of photons by deposited aerosol particles

Do Aerosols Influence Net Primary Productivity (NPP)?

gC m-2 yr-1

NPP = f(NDVI) * PAR * ε * g (T) * h (W)

•Deposition of Nitrogen to Nutrient Limited Ecosystems

•Acid Deposition

•UV Damage

•Transport of Nutrients to the Oceans (Fe)

•Climate Modification•Indirect Effect•Precipitation•Temperature

Other Possible Influences of Aerosols on Plants

FUTURE EFFORTS

•Field studies on various types of plants focusing on the relationship between variables that influence plant growth (T, precipitation, RH, nutrients) and quantity and quality of radiation

•Field and lab studies to look at influence of aerosol deposition on plant photosynthesis

•Development of new algorithms to predict NPP based on field observations

Research CollaboratorsGeorgia TechKarsten BaumannKip CarricoGlen CassBill ChamediesRoby GreenwaldC.S. KiangTed RussellRodney WeberJin Xu Jing Zhao

Cal TechLynn Salmon

Beijing UniversityX.Y. TangY.H. ZhangL. ZengC. Fang

Beijing EPBT. Yu

Linan BackgroundMet. StationG. LiuX. Yu

University of GeorgiaG. Hoogenboom