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BIOGENIC VOCs. TOPICS FOR TODAY. Why do we care about BVOCs? How are they climate-relevant? What are BVOCs? Why are they emitted? How do we measure BVOC emissions? How do we model BVOC emissions? How well do we understand BVOC emissions?

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BIOGENIC VOCs

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BIOGENIC VOCs


TOPICS FOR TODAY

  • Why do we care about BVOCs? How are they climate-relevant?

  • What are BVOCs? Why are they emitted?

  • How do we measure BVOC emissions?

  • How do we model BVOC emissions?

  • How well do we understand BVOC emissions?

  • How might BVOC emissions respond to a changing climate?


LARGE SUPPLY OF BIOGENIC VOCs – unrecognized until the 1990s

Switches polluted areas in U.S. from NOx-saturated to NOx-limited regime!

recognized in Revised Clean Air Act of 1999

Anthropogenic VOCs

Isoprene (biogenic VOC)

Jacob et al., [1993]


LATEST INVENTORIES OF BIOGENIC vs. ANTHROPOGENIC VOCs

…notice difference in scale!

Millet et al. [2007]


ISOPRENE: CONTROLLING AIR QUALITY AND CLIMATE

C5 H8: Reactive hydrocarbon emitted from plants (primarily broadleaf trees)

Annual global emissions ~ equivalent to methane emissions

CLIMATE

Depletes OH = ↑ CH4 lifetime

+ OH

O3

AIR QUALITY

Beijing

IPCC, 2007


TOPICS FOR TODAY

  • Why do we care about BVOCs? How are they climate-relevant?

  • What are BVOCs? Why are they emitted?

  • How do we measure BVOC emissions?

  • How do we model BVOC emissions?

  • How well do we understand BVOC emissions?

  • How might BVOC emissions respond to a changing climate?


GLOBAL ESTIMATES OF BIOGENIC NON-METHANE VOC EMISSIONSTotal: ~1250 Tg yr-1

Other non-

reactive VOCs

260 Tg

Isoprene

600 Tg

Other reactive

VOCs

260 Tg

Monoterpenes

130 Tg

Guenther et al. 1995; Guenther et al. 2006


WHICH BVOCs ARE IMPORTANT?

Christine Wiedinmyer, NCAR


BIOGENIC VOCs: MANY COMPOUNDS AND PATHWAYS

R. Fall 1999


PARTICULARLY “IMPORTANT” COMPOUNDS

Isoprene (C5H8)

Monoterpenes(C10H16)

Sesquiterpenes (C15H24)

MBO (2-methyl-3-buten-2-ol, C5H10O)


TOPICS FOR TODAY

  • Why do we care about BVOCs? How are they climate-relevant?

  • What are BVOCs? Why are they emitted?

  • How do we measure BVOC emissions?

  • How do we model BVOC emissions?

  • How well do we understand BVOC emissions?

  • How might BVOC emissions respond to a changing climate?


TOOLS FOR INVESTIGATING TRACE GAS FLUXES

Analysis using ambient concentrations, isotopes and oxidation products

Satellite data (e.g. HCHO)

Regional Characterization

Years

Process studies

Tower-based flux meas. systems

Days

Aircraft and blimp-based flux measurement systems

Enclosure

flux meas. systems

TIME SCALE

Hours

Seconds

Leaf

Canopy

Landscape

Regional/global

SPATIAL SCALE

Christine Wiedinmyer, NCAR


Leaf and Branch-Level Enclosure Studies


Above Canopy Flux Studies


Aircraft Studies


Satellite Studies: GOME HCHO

2.5x1016

molecules

cm-2

2

1.5

1

South

Atlantic

Anomaly

(disregard)

detection

limit

0.5

0

-0.5


TOPICS FOR TODAY

  • Why do we care about BVOCs? How are they climate-relevant?

  • What are BVOCs? Why are they emitted?

  • How do we measure BVOC emissions?

  • How do we model BVOC emissions?

  • How well do we understand BVOC emissions?

  • How might BVOC emissions respond to a changing climate?


MODELING BIOGENIC EMISSIONS: MEGAN

Model of Emissions of Gases and Aerosols from Nature

Guenther et al., 2006

  • Input files available at: http://cdp.ucar.edu


Model of Emissions of Gases and Aerosols from Nature: MEGAN

[Guenther et al., ACP, 2006]


Model of Emissions of Gases and Aerosols from Nature: MEGAN


HOW EMISSIONS ARE CALCULATED IN MEGAN

F: Emission Flux (g m-2 hr-1)

i: gridbox index

j: vegetation type index

: Emission Factor (g m-2 hr-1) at standard conditions for each vegetation type

: fractional area coverage of vegetation type

: Activity Factor (accounting for non-standard conditions)

: production/loss within canopy factor

Guenther et al., 2006


VEGEATION TYPES (PLANT FUNCTIONAL TYPES)

CLM landcover


PFT-SPECIFIC EMISSION FACTORS

On average, emission from broadleaf trees are 6x higher than needle evergreen, 20x higher than needle deciduous, and 2 orders of magnitude higher than crop emissions!

Guenther et al., 2006


BVOC EMISSIONS SCHEME

Flux = Emission Factor x Activity Factor ()

SOIL

MOISTURE

LIGHT

TEMPERATURE

LEAF AGE

ISOPRENE

MONTERPENES

[Guenther et al., 2006]

[Guenther et al., 1995]


ACTIVITY FACTORS: METEOROLOGICAL AND PHENOLOGICAL VARIABLES CONTROLLING EMISSION

  • LIGHT

  • Diffuse and direct radiation

  • Instantaneous and accumulated

    (24 hrs and 10 days)

  • TEMPERATURE (Leaf-level)

  • instantaneous and accumulated

    (24 hrs, 10 days)

T

L

T

PAR

AMOUNT OF VEGETATION

 Leaf area index (LAI)

  • LEAF AGE

  • Max emission = mature

  • Zero emission = new

LAI

SUMMER

Month

SOIL MOISTURE

 suppressed under drought

Guenther et al., 2006


GLOBAL DISTRIBUTION OF ISOPRENE EMISSIONS

Distinct seasonality due to vegetation cover and activity factors

Guenther et al., 2006


TOPICS FOR TODAY

  • Why do we care about BVOCs? How are they climate-relevant?

  • What are BVOCs? Why are they emitted?

  • How do we measure BVOC emissions?

  • How do we model BVOC emissions?

  • How well do we understand BVOC emissions?

  • How might BVOC emissions respond to a changing climate?


HOW WELL DO WE KNOW EMISSIONS?

  • How well to we know the rates of compounds we can currently measure?

  • What chemical species don’t we see?

  • Controlling variables?

    • Long-term Controls

    • Chemical Environment

    • Effects of stress

      • Drought

      • Oxidants

      • Herbivory

LOTS YET TO LEARN!


SPRING 2006 TERPENOID EMISSIONS FROM A EUCALYPTUS FOREST NEAR TUMBARUMBA AUSTRALIA

We are using the controlled environment of a growth chamber to investigate the processes controlling this behavior

Snowstorm

but not this

Models can predict this

A. Guenther


A MISSING FACTOR: ISOPRENE EMISSION INHIBITION BY CO2

Long-Term growth environment: gene adaptation

Dependent on ambient CO2

Short-term exposure: changes in metabolite pools and enzyme activity

Dependent on intercellular CO2

Empirical parameterization from plant studies: [Wilkinson et al., GCB, in press]

LESS Isoprene in a higher CO2 environment!


TOPICS FOR TODAY

  • Why do we care about BVOCs? How are they climate-relevant?

  • What are BVOCs? Why are they emitted?

  • How do we measure BVOC emissions?

  • How do we model BVOC emissions?

  • How well do we understand BVOC emissions?

  • How might BVOC emissions respond to a changing climate?


HOW WILL BVOC EMISSIONS RESPOND TO A FUTURE CLIMATE?

NPP ↑ Temperature↑

2000

2100

2000

2100-2000

Isoprene emissions projected to increase substantially due to warmer climate and increasing vegetation density.

Some/all of this negated by increasing CO2 concentrations…?

Heald et al. [2008]


WHAT IS THE IMPACT OF THESE INCREASING EMISSIONS?

NPP ↑ Temperature↑

2000

2100

Methane lifetime increases

[Shindell et al., 2007]

SOA burden ↑ > 20%

[Heald et al., 2008]

Surface O3 ↑ 10-30 ppb

[Sanderson et al., 2003]


Greener biosphere? Shift in vegetation northwards? Changing plant species?

ADDITIONAL COMPLICATION: CHANGING VEGETATION

CLM DGVM projects a 3x increase in LAI and a northward expansion of vegetation.

[Alo and Wang, 2008; Heald et al., in press]


OTHER UNKNOWN FACTOR: DISTURBANCE

Wildfires

Pine Beetle Outbreak

Kurz et al., 2008

Running et al., 2008


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