James Ryder

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Aim to develop a 1-dimensional transport and
chemistry model which simulates VOC chemistry and
aerosol formation within and above forest plant
canopies
James Ryder PhD Student, CEH Edinburgh
Manchester University
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1000m
z
Atmospheric boundary layer
Boxes of logarithmic height
Solar radiation
Chemistry scheme
20m
Emission of BVOCs
Canopy
Dry deposition
(Boxes of uniform height)
In canopy turbulence
Emission of NOx
0m
Ground level
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INITIAL CONDITIONS
Initial concentration of species, LAI profile,
box sizes, canopy height, co-ordinates of site
STEPPED PARAMETERS
Update boundary conditions (e.g. temperature,
radiation)
PAR, J(NO2), Temperature, Diffusion parameters
Re-calculate solar zenith angle and solar
intensity
Perform diffusion related functions over canopy
profile for all layers (separately for each
species)
next timestep
Perform chemistry, emission and deposition
related functions over all species (seperately
for each layer)
Concentration profiles for each species stored in
array
STEPPED OUTPUTS
Output data
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Key Parameterisations
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Turbulence Parameterisation

• Choices
• Modified K-Theory
• Near-field theory (Raupach, 1989 Makar, 1999)
• Random walk approach

Comparing the Localised Near Field Theory and the
Continuous Near Field Theory, Karl et al (2004)
found that on average the calculated deviation
between the 3 methods lies within a reasonable
uncertainty ( 20)
Comparison of the calculated concentrations
between the LNF (Raupach, 1986), CNF (Warland and
Thurtell, 2000) and random walk (Baldocchi et al,
1987). From Karl et al (2004)
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• Chemistry Scheme Parameterisation

The aim is to simulate the chemistry of VOCs and
aerosol creation. There are three categories of
SOA formation in atmospheric chemistry models

• Empirical data fits derived from lab chamber data
• The use of completely explicit gas-phase
  oxidation for the VOCs in question to predict the
  whole spectrum of condensing products
• The use of lumped gas-phase oxidation mechanisms
  derived from simplification of fully explicit
  mechanisms

Kanakidou et al (2005)
There are pros and cons to each of these methods,
including the lack of suitable measurement data
for many of the BVOCs
Comparison of SOA profiles as predicted by lab
based measurements (top/middle) and explicit
gas-phase mechanism (bottom) (Pun et al, 2003)
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• Other parameterisations

• Isoprene emission (Guenther, 1997 - based on PAR
  and temperature at leaf height)
• Monoterpene emission (Guenther et al, 1993 -
  based on temperature at leaf height)
• Sesquiterpene emission (Guenther et al, 1993 -
  based on temperature at leaf height)
• Gas and aerosol deposition (Karl or Meyers
  Baldocchi, 1988 both based on LAI profile)
• NO emission from forest floor (Manchester Uni
  will be conducting tropical forest soil emission
  measurements)

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Required field measurements
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In-canopy diffusion

• Measurements required
• ?w (standard deviation of vertical wind
  velocity)
• u? (friction velocity)

• Methodology
• sonic anemometer (CEH) at several measurement
  heights within dense canopy pump up mast or
  specially constructed tower
• Ideally multiple measurement sites repeat
  measurements over length of campaign

The diffusion step in the model solves the
equation
Vertical scalar flux density
Concentration field differential
Turbulent eddy diffusivity
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Canopy structure

• Measurements required
• LAI measurement profile
• Speciation of trees in canopy

• Methodology
• LI-COR 2000 (CEH) sensor at multiple measurement
  heights within dense canopy
• multiple measurement sites required. Further
  study using grid of ground-based measurements to
  gauge horizontal variation.

Contour map of the horizontal distribution of LAI
in a Panama tropical rainforest during the wet
season (Wirth et al, 2001)
The LAI profile is used to model emission and
deposition rates, and to calculate the
extinction factor for sunlight.
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Canopy speciation

• Measurements required
• Species of trees and plants at selected sites
• Emission inventories for these trees

• Methodology
• Co-ordinate with NCAR and US-EPA sub-project
  group to create emissions inventory
• Botanical survey of selected field sites
  (existing local species database could be used)

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Airborne Species Concentrations

• Measurements required
• In-canopy profiles of aerosols, VOCs and NOx/O3
• Above canopy aerosol flux, VOC flux

• Methodology
• In-canopy PTR-MS profiler system (movable inlet
  on pulleys)
• Above canopy AMS/GRAEGOR/PTR-MS/UHSAS/CPC from
  the main tower site

These measurements will be used to determine the
initial conditions in the chemistry scheme part
of the model and as a means to judge the
effectiveness of the parameterisations for VOC
emission and SOA formation
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PAR, J-values and Temperature

• Measurements required
• Canopy top Photo Active Radiation (PAR) values
  (continuous)
• In-canopy PAR values at different heights
• J-values for key photolytic reactions? J(NO2),
  J(O1D)
• Temperature profile for emission rate
• Humidity profile (?)

• Methodology
• PAR LICOR quantum sensor
• Measure J(NO2) with filter radiometer or infer
  values (Leicester and Leeds, poss. CEH)
• Measure site temperature fluctuations

Alternatively, clear sky J-values can be
derived from a 1D atmospheric radiative transfer
model, such as the TUV, and cloud factor values
inferred from the available literature.