Grantee Research Project Results
1997 Progress Report: Mathematical Models of the Transport and Fate of Airborne Organics
EPA Grant Number: R824970C004Subproject: this is subproject number 004 , established and managed by the Center Director under grant R824970
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: HSRC (1989) - Northeast HSRC
Center Director: Sidhu, Sukh S.
Title: Mathematical Models of the Transport and Fate of Airborne Organics
Investigators:
Institution:
EPA Project Officer:
Project Period: January 1, 1992 through June 30, 1997
Project Period Covered by this Report: January 1, 1996 through June 30, 1997
Project Amount: Refer to main center abstract for funding details.
RFA: Center on Airborne Organics (1993) Recipients Lists
Research Category: Targeted Research
Objective:
The goal of this research is to develop a new mathematical and computational framework for the systematic sensitivity and uncertainty analysis of the complex transport and transformation processes that control the concentration dynamics of airborne organics. A particular focus is the implementation of numerical procedures that are much more computationally efficient than even the best Monte Carlo sampling strategies. Once the tools have been developed, the approach is to carry out a detailed investigation of the photochemical oxidation mechanics for aromatic compounds.Rationale: One of the consequences of using models to describe the formation and transport of photochemical air pollution is that some approximations are involved. In addition, there are also measurement errors in the data used to develop inputs and kinetic parameters for the reaction mechanisms. The key issue is not that uncertainties are involved, they will always be present, but to identify which of the inputs contributes most to the uncertainty in predictions. The present set of tools available to the research community are simply computationally intractable for the complex reaction schemes needed to describe the photochemistry of airborne organics.
Approach: In this research a new approach termed the Deterministically Equivalent Modeling Method (DEMM) has been developed. Uncertain parameters are treated as random variables that are in turn approximated using orthogonal basis function expansions in the probability space. For example, if the uncertain inputs are independent and Gaussian-distributed, the expansion is based on standard Hermite polynomials. A complete description of the method is contained in Tatang (1994). The utility of the DEMM -- Collocation approach in conducting uncertainty analyses of large, "black box" type models was demonstrated last year using the Statewide Air Pollution Research Center (SAPRC) mechanism which has over a hundred uncertain parameters.
Status: Set out below are accomplishments of the project work in 1996 - 97 (termination):
? The effects of uncertain isoprene reactions were investigated by comparing the current Regional Acid Deposition Model (RADM) and a mechanism supplement with explicit reactions of isoprene and its products. Explicit treatment of isoprene reactions was important for the characterization of the effects of uncertain parameters on the predictions. In addition to the total amount of isoprene, uncertainties in the product coefficients of secondary carbonyls compounds, methacrolein and methyl vinyl ketone, also contributed to uncertainties in the predictions of ozone and other photochemically-reactive compounds.
? The DEMM -- collocation approach was applied to three atmospheric mechanisms with different design assumptions. A comparison of the uncertain predictions of the SAPRC, RADM, and Carbon Bond IV (CB4) mechanisms showed that the predictions are indistinguishable given the effects of current parametric uncertainties. Any observations could be reproduced by the mechanisms using parameters that were within their ranges of uncertainties. Therefore, a research priority should be to reduce parametric uncertainties of the key variance-contributing parameters in these mechanisms.
? The uncertainties in the predictions of the three-dimensional CIT Airshed model due to uncertainties in the chemical processes were investigated. The uncertainties in the predicted ozone concentrations due to uncertain chemical parameters were about 25% of the nominal value. This uncertainty did not explain the discrepancies between model predictions and field observations. Other sources of model and data uncertainties dominate the predictions and / or observations.
? The same set of uncertain parameters contributed to uncertain predictions of all three mechanisms investigated and the CIT Airshed model. The variance-contributing inputs included: photolysis rates of NO2 and HCHO, the initial condition / sources of NOx and the reaction rates of HO + NO2 and PAN reactions.
Uncertainty analysis is a valuable tool to understand and differentiate models. DEMM was applied in a series of uncertainty analyses to identify chemical parameters that contribute to uncertain model predictions. Priorities for field and laboratory studies can be set accordingly. This type of analysis can be extended to a wide range of chemical and environmental problems.
Key Personnel
Graduate Student: Betty Pun
Supplemental Keywords:
RFA, Scientific Discipline, Air, Waste, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Mathematics, Environmental Chemistry, Fate & Transport, Atmospheric Sciences, particulates, fate and transport, mathematical model, air quality models, ambient measurement methods, airborne organics, atmospheric transformation, air pollution, deterministically equivalent modeling method, atmospheric transport, particle transportProgress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R824970 HSRC (1989) - Northeast HSRC Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R824970C001 Chemical Kinetic Modeling of Formation of Products of Incomplete Combustion
from Spark-ignition Engines
R824970C002 Combustion Chamber Deposit Effects on Engine Hydrocarbon Emissions
R824970C003 Atmospheric Transformation of Volatile Organic Compounds: Gas-Phase
Photooxidation and Gas-to-Particle Conversion
R824970C004 Mathematical Models of the Transport and Fate of Airborne Organics
R824970C005 Elementary Reaction Mechanism and Pathways for Atmospheric Reactions
of Aromatics - Benzene and Toluene
R824970C006 Simultaneous Removal of Soot and NOx from the Exhaust of Diesel Powered
Vehicles
R824970C007 Modeling Gas-Phase Chemistry and Heterogeneous Reaction of Polycyclic
Aromatic Compounds
R824970C008 Fundamental Study on High Temperature Chemistry of Oxygenated Hydrocarbons
as Alternate Motor Fuels and Additives
R824970C009 Markers for Emissions from Combustion Sources
R824970C010 Experimental Investigation of the Evolution of the Size and Composition Distribution of Atmospheric Organic Aerosols
R824970C011 Microengineered Mass Spectrometer for in-situ Measurement of Airborne
Contaminants
The 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.
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- Original Abstract
125 publications for this center
89 journal articles for this center