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Title: A Computational Approach to Understanding Aerosol Formation and Oxidant Chemistry in the Troposphere

Abstract

An understanding of the mechanisms and kinetics of aerosol formation and ozone production in the troposphere is currently a high priority because these phenomena are recognized as two major effects of energy-related air pollution. Atmospheric aerosols are of concern because of their effect on visibility, climate, and human health. Equally important, aerosols can change the chemistry of the atmosphere, in dramatic fashion, by providing new chemical pathways (in the condensed phase) unavailable in the gas phase. The oxidation of volatile organic compounds (VOCs) and inorganic compounds (e.g., sulfuric acid, ammonia, nitric acid, ions, and mineral) can produce precursor molecules that act as nucleation seeds. The U.S. Department of Energy (DOE) Atmospheric Chemistry Program (ACP) has identified the need to evaluate the causes of variations in tropospheric aerosol chemical composition and concentrations, including determining the sources of aerosol particles and the fraction of such that are of primary and secondary origin. In particular, the ACP has called for a deeper understanding into aerosol formation because nucleation creates substantial concentrations of fresh particles that, via growth and coagulation, influence the Earth's radiation budget. Tropospheric ozone is also of concern primarily because of its impact on human health. Ozone levels are controlled bymore » NOx and by VOCs in the lower troposphere. The VOCs can be either from natural emissions from such sources as vegetation and phytoplankton or from anthropogenic sources such as automobiles and oil-fueled power production plants. The major oxidant for VOCs in the atmosphere is the OH radical. With the increase in VOC emissions, there is rising concern regarding the available abundance of HOx species needed to initiate oxidation. Over the last five years, there have been four field studies aimed at initial measurements of HOx species (OH and HO? radicals). These measurements revealed HOx levels that are two to four times higher than expected from the commonly assumed primary sources. Such elevated abundances of HOx imply a more photochemically active troposphere than previously thought. This implies that rates of ozone formation in the lower region of the atmosphere and the oxidation of SO? can be enhanced, thus promoting the formation of new aerosol properties. Central to unraveling this chemistry is the ability to assess the photochemical product distributions resulting from the photodissociation of by-products of VOC oxidation. We propose to use state-of-the-art theoretical techniques to develop a detailed understanding of the mechanisms of aerosol formation in multicomponent (mixed chemical) systems and the photochemistry of atmospheric organic species. The aerosol studies involve an approach that determines homogeneous gas-particle nucleation rates from knowledge of the molecular interactions that are used to define properties of molecular clusters. Over the past several years we developed Dynamical Nucleation Theory (DNT), a novel advance in the theoretical description of homogeneous gas-liquid nucleation, and applied it to gas-liquid nucleation of a single component system (e.g., water). The goal of the present research is to build upon these advances by extending the theory to multicomponent systems important in the atmosphere (such as clusters containing sulfuric acid, water, ions, ammonia, and organics). In addition, high-level ab initio electronic structure calculations will be used to unravel the chemical reactivity of the OH radical and water clusters.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
881691
Report Number(s):
PNNL-15772
2393; KP1303000; TRN: US200613%%147
DOE Contract Number:
AC05-76RL01830
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; AEROSOLS; AIR POLLUTION; ATMOSPHERIC CHEMISTRY; CHEMICAL COMPOSITION; CHEMISTRY; ELECTRONIC STRUCTURE; INORGANIC COMPOUNDS; MOLECULAR CLUSTERS; NITRIC ACID; ORGANIC COMPOUNDS; OXIDIZERS; POWER GENERATION; SULFURIC ACID; TROPOSPHERE; VOLATILE MATTER; Environmental Molecular Sciences Laboratory

Citation Formats

Francisco, Joseph S., Kathmann, Shawn M., Schenter, Gregory K., Dang, Liem X., Xantheas, Sotiris S., Garrett, Bruce C., Du, Shiyu, Dixon, David A., Bianco, Roberto, Wang, Shuzhi, Hynes, James T., Morita, Akihiro, and Peterson, Kirk A.. A Computational Approach to Understanding Aerosol Formation and Oxidant Chemistry in the Troposphere. United States: N. p., 2006. Web. doi:10.2172/881691.
Francisco, Joseph S., Kathmann, Shawn M., Schenter, Gregory K., Dang, Liem X., Xantheas, Sotiris S., Garrett, Bruce C., Du, Shiyu, Dixon, David A., Bianco, Roberto, Wang, Shuzhi, Hynes, James T., Morita, Akihiro, & Peterson, Kirk A.. A Computational Approach to Understanding Aerosol Formation and Oxidant Chemistry in the Troposphere. United States. doi:10.2172/881691.
Francisco, Joseph S., Kathmann, Shawn M., Schenter, Gregory K., Dang, Liem X., Xantheas, Sotiris S., Garrett, Bruce C., Du, Shiyu, Dixon, David A., Bianco, Roberto, Wang, Shuzhi, Hynes, James T., Morita, Akihiro, and Peterson, Kirk A.. Tue . "A Computational Approach to Understanding Aerosol Formation and Oxidant Chemistry in the Troposphere". United States. doi:10.2172/881691. https://www.osti.gov/servlets/purl/881691.
@article{osti_881691,
title = {A Computational Approach to Understanding Aerosol Formation and Oxidant Chemistry in the Troposphere},
author = {Francisco, Joseph S. and Kathmann, Shawn M. and Schenter, Gregory K. and Dang, Liem X. and Xantheas, Sotiris S. and Garrett, Bruce C. and Du, Shiyu and Dixon, David A. and Bianco, Roberto and Wang, Shuzhi and Hynes, James T. and Morita, Akihiro and Peterson, Kirk A.},
abstractNote = {An understanding of the mechanisms and kinetics of aerosol formation and ozone production in the troposphere is currently a high priority because these phenomena are recognized as two major effects of energy-related air pollution. Atmospheric aerosols are of concern because of their effect on visibility, climate, and human health. Equally important, aerosols can change the chemistry of the atmosphere, in dramatic fashion, by providing new chemical pathways (in the condensed phase) unavailable in the gas phase. The oxidation of volatile organic compounds (VOCs) and inorganic compounds (e.g., sulfuric acid, ammonia, nitric acid, ions, and mineral) can produce precursor molecules that act as nucleation seeds. The U.S. Department of Energy (DOE) Atmospheric Chemistry Program (ACP) has identified the need to evaluate the causes of variations in tropospheric aerosol chemical composition and concentrations, including determining the sources of aerosol particles and the fraction of such that are of primary and secondary origin. In particular, the ACP has called for a deeper understanding into aerosol formation because nucleation creates substantial concentrations of fresh particles that, via growth and coagulation, influence the Earth's radiation budget. Tropospheric ozone is also of concern primarily because of its impact on human health. Ozone levels are controlled by NOx and by VOCs in the lower troposphere. The VOCs can be either from natural emissions from such sources as vegetation and phytoplankton or from anthropogenic sources such as automobiles and oil-fueled power production plants. The major oxidant for VOCs in the atmosphere is the OH radical. With the increase in VOC emissions, there is rising concern regarding the available abundance of HOx species needed to initiate oxidation. Over the last five years, there have been four field studies aimed at initial measurements of HOx species (OH and HO? radicals). These measurements revealed HOx levels that are two to four times higher than expected from the commonly assumed primary sources. Such elevated abundances of HOx imply a more photochemically active troposphere than previously thought. This implies that rates of ozone formation in the lower region of the atmosphere and the oxidation of SO? can be enhanced, thus promoting the formation of new aerosol properties. Central to unraveling this chemistry is the ability to assess the photochemical product distributions resulting from the photodissociation of by-products of VOC oxidation. We propose to use state-of-the-art theoretical techniques to develop a detailed understanding of the mechanisms of aerosol formation in multicomponent (mixed chemical) systems and the photochemistry of atmospheric organic species. The aerosol studies involve an approach that determines homogeneous gas-particle nucleation rates from knowledge of the molecular interactions that are used to define properties of molecular clusters. Over the past several years we developed Dynamical Nucleation Theory (DNT), a novel advance in the theoretical description of homogeneous gas-liquid nucleation, and applied it to gas-liquid nucleation of a single component system (e.g., water). The goal of the present research is to build upon these advances by extending the theory to multicomponent systems important in the atmosphere (such as clusters containing sulfuric acid, water, ions, ammonia, and organics). In addition, high-level ab initio electronic structure calculations will be used to unravel the chemical reactivity of the OH radical and water clusters.},
doi = {10.2172/881691},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Apr 18 00:00:00 EDT 2006},
month = {Tue Apr 18 00:00:00 EDT 2006}
}

Technical Report:

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  • Ozone production and aerosol formation in the troposphere are recognized as two major effects of energy-related air pollutants. Tropospheric ozone is of concern primarily because of its impact on health. Ozone levels are controlled by NOx and by volatile organic compounds (VOCs) in the lower troposphere. The VOCs can either be from natural emissions from such sources as vegetation and phytoplankton or from anthropogenic sources such as automobiles and oil-fueled power production plants. It is of critical importance to the Department of Energy (DOE) in developing national energy use policies to understand the role of VOCs in determining air qualitymore » and how VOC emission or NOx emission control strategies should be designed.« less
  • Global radiative forcing of nitrate and ammonium aerosols has mostly been estimated from aerosol concentrations calculated at thermodynamic equilibrium or using approximate treatments for their uptake by aerosols. In this study, a more accurate hybrid dynamical approach (DYN) was used to simulate the uptake of nitrate and ammonium by aerosols and the interaction with tropospheric reactive nitrogen chemistry in a three-dimensional global aerosol and chemistry model, IMPACT, which also treats sulfate, sea salt and mineral dust aerosol. 43% of the global annual average nitrate aerosol burden, 0.16 TgN, and 92% of the global annual average ammonium aerosol burden, 0.29 TgN,more » exist in the fine mode (D<1.25 {micro}m) that scatters most efficiently. Results from an equilibrium calculation differ significantly from those of DYN since the fraction of fine-mode nitrate to total nitrate (gas plus aerosol) is 9.8%, compared to 13% in DYN. Our results suggest that the estimates of aerosol forcing from equilibrium concentrations will be underestimated. We also show that two common approaches used to treat nitrate and ammonium in aerosol in global models, including the first-order gas-to-particle approximation based on uptake coefficients (UPTAKE) and a hybrid method that combines the former with an equilibrium model (HYB), significantly overpredict the nitrate uptake by aerosols especially that by coarse particles, resulting in total nitrate aerosol burdens higher than that in DYN by +106% and +47%, respectively. Thus, nitrate aerosol in the coarse mode calculated by HYB is 0.18 Tg N, a factor of 2 more than that in DYN (0.086 Tg N). Excessive formation of the coarse-mode nitrate in HYB leads to near surface nitrate concentrations in the fine mode lower than that in DYN by up to 50% over continents. In addition, near-surface HNO{sub 3} and NO{sub x} concentrations are underpredicted by HYB by up to 90% and 5%, respectively. UPTAKE overpredicts the NO{sub x} burden by 56% and near-surface NO{sub x} concentrations by a factor of 2-5. These results suggest the importance of using the more accurate hybrid dynamical method in the estimates of both aerosol forcing and tropospheric ozone chemistry.« less
  • The overall objective of the work is to provide basic underpinning research that will contribute to a quantification of the behavior of pollutants and radionuclides associated with advanced energy activities after these materials emanate from their source and are transferred through the environment to the biota and human receptor. Data is being acquired on photoinduced transformation of pollutants including reactions which take place on aerosol particles, as well as those of species which become transformed into aerosols as a result of their chemical and physical interactions. The studies also provide critical information on problems in radiation biology and include investigationsmore » of reactions of molecules, which simulate functional groups in biological systems, as they proceed following the absorption of ionizing radiation.« less
  • The small cluster program involves (1) studies of reactions related to formation and growth of heteromolecular clusters and their thermochemical properties, (2) studies of photoinitiated processes in clusters, (3) investigations related to heterogeneous reactions including the influence of reaction centers on the interconversion, and (4) theoretical calculations of properties, dynamics, and structure. A major thrust of the work during the past year has been devoted to a study of the role of ionization and the presence of ions on reactions and energetics. During the past few months, particular attention has been paid to systems having varying proton affinities. From themore » data, we can determine the influence of these values on the nature of the reactions and ascertain the ultimate chemical nature of the ionization center formed as a result of the reactions. 83 refs., 12 figs., 2 tabs.« less
  • Chemical reactions that proceed following either a photophysical or ionizing event, are directly influenced by the mechanisms of energy transfer and dissipation away from the primary site of absorption. Neighboring solvent or solute molecules can affect this by collisional deactivation (removal of energy), through effects in which dissociating molecules are kept in relatively close proximity for comparatively long periods of time due to the presence of the solvent, and in other ways where the solvent influences the energetics of the reaction coordinate. Research on clusters offers one of the most viable ways of elucidating the molecular details of these processes.more » The current program is comprised of three general areas of research. Investigation of the dynamics of ionization and the mechanisms of the early-time reactions following the interaction of ionizing electromagnetic radiation with matter; measurement of the kinetics of ensuing ion reactions with effort focused on the influence of solvation effects and identifying similarities and differences between gas and condensed phase reactions; and determination of the structure of solvated reaction centers via spectroscopy, dynamics and thermochemistry.« less