GFDL - Geophysical Fluid Dynamics Laboratory

Larry W. Horowitz – Research

I am a Physical Scientist at the NOAA
Geophysical Fluid Dynamics Laboratory (GFDL).
My research focuses on the chemistry of tropospheric ozone and related species.
On this page, I describe the goals of my research, and some of the techniques I
use to address these goals.

View my MOZART-2 web
, describing the model I use in my research.

You can also view:

Ozone (O3) is of central importance to the chemistry of the troposphere.
Ozone is:

  • a major air pollutant, detrimental to public health and vegetations
  • the precursor of the hydroxyl radical, which is the primary oxidant in the
  • climatically-important greenhouse gas

Ozone is produced within the troposphere as the result of reactions involving nitrogen
oxides (NOx), carbon monoxide, and hydrocarbons. Increases in the emissions
of these ozone precursors over the past century (from fossil fuel and biomass burning)
are believed to have resulted in increases in tropospheric ozone concentrations
over industrial regions, and probably on a global scale.

Major questions my research addresses include:

  • What controls the global distribution of ozone in the troposphere?
  • How have anthropogenic emissions altered the distribution of ozone?
  • What role does deep convection in the tropics play in controlling the production
    of ozone in the upper troposphere?
  • What impact do changes in tropospheric ozone have on climate?
  • How will projected future emission scenarios alter the chemistry of the
  • How does the oxidizing capacity of the atmosphere change in response to
    varying anthropogenic emissions?

In order to answer these questions, I am using a global three-dimensional chemical
transport model (called MOZART) to
simulate the distributions of ozone and its chemical precursors throughout the troposphere.
Using MOZART, and comparing model results with observations, I plan to test of our
understanding of chemical and dynamical processes in the atmosphere. A goal of my
work is to improve our understanding of the complex nonlinear dependence of ozone
concentrations on emissions from sources such as fossil fuel combustion and biomass

The oxidizing capacity of the atmosphere, which is the ability of the atmosphere
to remove pollutants emitted, depends heavily on the abundance of ozone in the tropics.
However, there have been relatively few measurements of ozone and its precursors
in the tropical troposphere. As a result, the mechanisms controlling ozone in this
region are poorly understood. Global three-dimensional models can be of great use
in helping to explain these mechanisms in a manner consistent with the few available
observations. Future land use changes and industrialization in the tropics are expected
to lead to an increased anthropogenic perturbation to ozone in this region. There
is a complicated interaction in the tropics between surface emissions, convection,
lightning, and large-scale circulation. Using MOZART, which contains representations
of all of these processes, together with available observations of ozone and its
precursors in the tropics, I plan to study the mechanisms controlling the distribution
of tropical tropospheric ozone. I will also evaluate how well these various processes
are currently represented in global chemistry models.

I got my Ph.D. from the Atmospheric Sciences
in the Division of Engineering
and Applied Sciences
at Harvard University.
My advisor was Professor
Daniel Jacob
. In my dissertation research, I utilized a variety of models to
study tropospheric chemistry. In my early work, I used a photochemical model to
perform 0-dimensional and 1-dimensional simulations. I updated our photo-oxidation
mechanism for isoprene and studied the effects of these modifications on the production
of ozone and organic nitrates, using comparisons with observations as a guide. I
also developed a simplified chemical mechanism for incorporation into a 3-dimensional
chemical tracer model, and evaluated the accuracy of this mechanism against our
complete mechanism. I developed and used both continental-scale and global versions
of this model to study the export of reactive nitrogen from the continental boundary
layer and its effect on the abundance of nitrogen oxides in the remote troposphere.

You can view my
thesis abstract and introduction
(in pdf format).

Back to my Home Page

Larry Horowitz /