Grantee Research Project Results
1999 Progress Report: Chemical-Transport Modeling of the Global Atmosphere Environmental Problems: Evaluations, Comparisons and Initial Studies
EPA Grant Number: R826384Title: Chemical-Transport Modeling of the Global Atmosphere Environmental Problems: Evaluations, Comparisons and Initial Studies
Investigators: Wuebbles, Donald J. , Kotamarthi, V. Rao
Institution: University of Illinois Urbana-Champaign
EPA Project Officer: Hahn, Intaek
Project Period: April 1, 1998 through March 31, 2001
Project Period Covered by this Report: April 1, 1998 through March 31, 1999
Project Amount: $312,334
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Safer Chemicals
Objective:
We are coordinating with the National Center for Atmospheric Research (NCAR) in the development, testing, and evaluation of a new three-dimensional chemical-transport model that will greatly increase the capabilities for dealing with global atmospheric issues of interest to the U.S. Environmental Protection Agency (EPA). Initial studies test and evaluate the model in comparison with available observations. Initial research studies with the model focus primarily on the oxidizing capacity of the atmosphere. Many compounds, including most of the replacement compounds being used and/or considered for chlorofluorocarbons (CFCs), halons, and other controlled chemicals are designed to react in the troposphere, largely with OH. Improved understanding of the oxidative capacity of the atmosphere is essential for estimating the lifetimes of these compounds correctly and to predict the fate of their degradation products in the troposphere. The sensitivity of model calculated tropical oxidant concentrations to perturbations, including biomass burning, will be investigated. The calculated oxidant field will be tested with an off-line simulation of CH3CCl3 and compared with observations. Sensitivity of model calculated lifetimes of short-lived (~ months) replacements to temporal and spatial variabilities of the source will be investigated. We expect as a result of this project to reduce the uncertainties in calculating the tropospheric lifetimes of such replacement compounds and to provide an improved understanding of the oxidizing capacity of the atmosphere and the changes that may be occurring to it.Progress Summary:
In the first year of the grant, we primarily analyzed and tested the initial MOZART (Model for OZone And otheR Trace gases) model in coordination with scientists at NCAR. We also developed a version of the model for massively parallel computational platforms. These studies then led to development of the next generation of the model, called MOZART-2. Initial studies focused again on testing and evaluating this model. For example, an analysis was made of the hydroxyl distribution in the model compared to other analyses of the tropospheric distribution of OH. Several areas of concern were found, but overall the model compares well with the available data analyses (see Johnson, 2000, for more discussion). The model also compares well with available radon data in the troposphere. However, there remain some concerns about the ozone and NOx distributions that we are still trying to resolve.
The MOZART2 model is being used to evaluate the tropical Southern Pacific using two recently concluded field experiments conducted by the National Aeronautics and Space Administration (NASA). Measurements made during two data collection campaigns sponsored by NASA, PEM-TROPICS A and B (Pacific Exploratory Mission in the Tropics), conducted over two different periods of the year corresponding to fall (September/October 1996) and spring (March/April 1999) in the southern hemisphere under the Global Tropospheric Experiment (GTE) program, are used for evaluating the model results. Other data sets for this period, including ozone profiles from SHADOZ (Southern Hemisphere ADditional OZone Sondes) and measurements of CO and ozone made by National Oceanic and Atmospheric Administration (NOAA) Climate Monitoring and Diagnostics Laboratory (CMDL), also are used in this evaluation. The primary focus of the study is to address the following key scientific issues: What controls the ozone budget in the southern tropics? What is the significance of advected fluxes of ozone and precursors into the Northeast Pacific box and Southwest Pacific of the southern-hemisphere in determining the local ozone levels? What is the magnitude of ozone in situ production/loss? What is the significance of transport from stratosphere in relation to in situ production and long-range transport from the NH/South America/South Africa/Southeast Asia? What is the role of the Intertropical Convergence Zone (ITCZ) and South Pacific Convergence Zone (SPCZ) in controlling the inter-hemispheric transport? A journal article is being sent to the Journal of Geophysical Research and a number of presentations have been made relating to these studies.
MOZART2 also is being used in studies to examine the ozone depletion potentials (ODP) of n-propyl bromide (nPB), a compound of current interest to EPA for policy considerations. A number of the compounds being proposed as replacements for substances controlled under the Montreal Protocol have extremely short atmospheric lifetimes, on the order of days to a few months. This particular compound, useful as a solvent, has an atmospheric lifetime of less than 20 days due to its reaction with hydroxyl. Because nPB contains bromine, any amount reaching the stratosphere has the potential to affect concentrations of stratospheric ozone. The definition of ODP also is being modified for such short-lived compounds to account for the location and timing of emissions. It is not adequate to treat these chemicals as if they were uniformly emitted at all latitudes and longitudes as normally done for longer-lived gases. Thus, for short-lived compounds, the single ODP generally provided to policymakers will need to be replaced with a table of ODP values. This study uses the MOZART2 three-dimensional chemical-transport model in combination with studies with our less computationally expensive two-dimensional model to examine potential effects of nPB on stratospheric ozone. Multiple facets of this study examine key questions regarding the amount of bromine reaching the stratosphere following emission of nPB. First, we examine the question of whether tropospheric oxidation of nPB could produce intermediate products that survive long enough to transfer bromine into the stratosphere. Second, we evaluate whether inorganic bromine (Br) produced from nPB oxidation in the troposphere could reach the stratosphere in meaningful quantities and thus affect stratospheric ozone. Third, we examine to what degree the land-based sources of nPB could affect the amount of Br transported to the stratosphere relative to the zonally-averaged emissions assumed in the two-dimensional modeling approach. Finally, we examine the resulting ODPs for nPB as a function of where emissions occur.
Future Activities:
Using MOZART-2, we will continue the analyses on the long-range transport of pollutants and their effects on the oxidation capacity of the atmosphere. Studies will be expanded to include further analyses with PEM-TROPICS A and B data, while also bringing in other datasets such as the measurements from the BIBLE campaign being sponsored by Japan. Analyses with the model also continue to evaluate its capabilities in treating convective processes, boundary layer processes, and dry and wet deposition. Tropospheric chlorine and bromine chemistry are being added to the model. We also are continuing our analyses of how well the model can treat short-lived chemicals of interest to policy considerations at EPA. Meanwhile, we also are coordinating with NCAR in development of the next generation MOZART-3 model, which will include a complete stratosphere, and allow us to extend our capabilities for studies of CFC and halon replacement compounds and their potential effects on ozone.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 19 publications | 5 publications in selected types | All 4 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Kotamarthi VR, Wuebbles DJ, Reck RA. Effects of nonmethane hydrocarbons on lower stratospheric and upper tropospheric chemical climatology in a two-dimensional zonal average model. Journal of Geophysical Research: Atmospheres 1999;104(D17):21537-21547. |
R826384 (1999) R826384 (Final) |
Exit Exit |
Supplemental Keywords:
global warming, nitrogen budget, semi-volatile organochlorines, oxidizing capacity, long-range transport of pollutants, Ozone Depletion Potentials, South Pacific, global climate change, modeling., RFA, Scientific Discipline, Air, Toxics, Ecology, Environmental Chemistry, climate change, Chemistry, CFCs, Engineering, Chemistry, & Physics, fate, environmental monitoring, atmospheric particles, global scale, global change, global warming calculations, three dimensional transport model, chemical transport modeling, organochlorides, chemical kinetics, halons, chemical transport models, nitrogen removal, oxidant, troposphereProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.