Chemistry, aerosols, ad dynamics
interactions research
(top)
The foci of studies on chemistry, aerosols, and dynamics
interactions are to examine the effect of physical and dynamical
processes on chemical species and to study the effect of
chemistry on aerosols and cloud condensation nuclei. Ongoing
projects within the program include studies of the effects
of boundary layer processes on chemical species distributions,
cloud chemistry process studies, and prediction of chemical
constituents on the cloud scale to mesoscale.
Simple prediction of mean profiles and fluctuations of
reactive species
Donald Lenschow, David Gurarie (Case Western Reserve University),
and Ian Faloona (University of California, Davis) continued
to work on a simple one-dimensional global model that predicts
mean vertical structure and fluctuations in trace gas concentrations
as a function of species lifetime in the atmosphere. In comparison
with full-blown three-dimensional global models, simplified
models are much easier to handle both analytically and numerically.
Thus, extensive experiments and simulations can be run with
simplified models and applied, for example, to inverse problems
(determination of sources, sinks, transport, or chemistry
from observed concentrations). The latest version incorporates
the parameterized effects of cumulus convection on vertical
transport throughout the free troposphere using results from
a three-dimensional global model provided by Natalie Mahowald
(CGD). Comparisons with aircraft-based observational studies
of mean profiles show good agreement with some species, but
poor agreement with others. At this point, the researchers
do not know whether the disagreement is due to insufficient
knowledge of the species lifetime as a function of height
or to problems with the model.
Effect of boundary layer processes on chemical species
distributions (top)
Large-eddy simulation (LES) coupled with gas-phase chemistry
The segregation of chemical species that is induced by turbulence
is being examined with a large-eddy simulation (LES) coupled
with gas-phase chemistry by Mary
Barth and Edward Patton (visitor,
Pennsylvania State University). The project focuses on
the covariance of isoprene and hydroxyl radical,
species whose reaction plays an important role in ozone production.
The processes that produce and destroy the covariance of
these two species are being analyzed to explain why the species
are segregated under some chemical scenarios, but not under
others. The results suggest that the covariance of isoprene
and hydroxyl radical is tied to the covariance of isoprene
and nitric oxide since oxidation of nitric oxide maintains
hydroxyl radical concentrations. Barth,
Si-Wan Kim (visitor, Seoul University, Korea), Patton,
and Moeng modified the
LES coupled with chemistry to simulate cloud physics and
aqueous chemistry. These modifications
include improving the gas and aqueous-phase chemical reaction
schemes to represent hydrocarbon chemistry more realistically.
Studies of the chemical transport and transformation in the
environment of continental fair-weather cumulus are being
performed.
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| Figure 49: Cross-sectional
(x-y) views of cloud and formic acid concentrations.
(a) Average
liquid water content in the cloud layer predicted by
the LES. (b) Average aqueous-phase formic acid (HCOOH)
mixing ratios in the cloud layer. (c) Average total (gas
+ aqueous) formic acid mixing ratios in the cloud and
boundary layers. The minimum and maximum values of each
variable are given at the top of each panel. Note that
aqueous-phase HCOOH is well correlated with the liquid
water content, while total HCOOH also resides in regions
downwind of clouds. |
The importance of the cloud drop representation on
cloud chemistry (top) Chemical constituent concentrations compared to numerical
simulations in representation of cloud drops
To determine whether representing a cloud drop population
with different sizes and pH values produces chemical constituent
concentrations that are substantially different from numerical
simulations which represent cloud drops with a single mean
size and pH value, Mary Barth and
Roberto Cancel (SOARS student) have combined cloud parcel
physics simulations with cloud
chemistry simulations. The activation and growth of cloud
drops are simulated by a cloud parcel model that represents
a spectrum of cloud condensation nuclei. Its output, drop
size and water content, is used in a gas-aqueous photochemistry
model. The cloud chemistry is simulated as 1) a bulk water
calculation with drop radius set to ten microns, and 2) a
population of drops with varying sizes. Preliminary results
indicate that differences in several reactive, soluble species
(e.g., formaldehyde, formic acid) occur between the two microphysics
parameterizations.
Cloud chemistry process studies (top)
Cloud parcel model upgraded to include the representation
of multicomponent aerosols,
and aerosol physics and chemistry
In collaboration with Mary Barth,
Craig Stroud (ACD/ASP), Kristy Ross (postdoctoral visiting
scientist University of the Witwatersrand,
South Africa), and Roelof Bruintjes,
are upgrading the cloud parcel model to include the representation
of multicomponent
aerosols and aerosol physics and chemistry. Barth is
incorporating gas and aqueous chemistry into the cloud parcel
model. The
model will be used to investigate the effect of aerosol chemistry
on cloud drop activation and the effect of cloud chemistry
on the cloud condensation nuclei composition. It will be
evaluated with field measurements.
Cloudscale and mesoscale prediction of chemical constituents (top)
WRF-chem, a coupled meteorology and chemistry model
Mary Barth and William
Skamarock developed
plans for using WRF-chem, a coupled meteorology and chemistry
model, as a convective
cloud-scale model to examine the flux of a variety of species
to the upper troposphere and in precipitation at the surface.
These plans, which were outlined in an opportunity fund proposal,
include implementing code describing cloud chemistry into
WRF-chem (in collaboration with XueXi Tie, Sasha Madronich
(both in ACD), and Georg Grell (NOAA/FSL)), simulating the
chemistry in and near convective storms, and evaluating the
simulation results with observations from the Stratosphere-Troposphere
Experiments: Radiation, Aerosols, and Ozone (STERAO) field
campaign. In addition, collaborations with Phil Rasch
(CGD) and university scientists (Chien Wang,
MIT and others) are being established to coordinate investigations
of tracer transport in convection as simulated in convective
cloud models and in large-scale models.
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