Modeling Of Atmospheric Processes Research Articles

Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2-SURF): Degradation of polycyclic aromatic hydrocarbons exposed to O<sub>3</sub>, NO<sub>2</sub>, H<sub>2</sub>O, OH and NO<sub>3</sub>

Abstract. We present a kinetic double-layer surface model (K2-SURF) that describes the degradation of polycyclic aromatic hydrocarbons (PAHs) on aerosol particles exposed to ozone, nitrogen dioxide, water vapor, hydroxyl and nitrate radicals. The model is based on multiple experimental studies of PAH degradation and on the PRA framework (Pöschl-Rudich-Ammann, 2007) for aerosol and cloud surface chemistry and gas-particle interactions. For a wide range of substrates, including solid and liquid organic and inorganic substances (soot, silica, sodium chloride, octanol/decanol, organic acids, etc.), the concentration- and time-dependence of the heterogeneous reaction between PAHs and O3 can be efficiently described with a Langmuir-Hinshelwood-type mechanism. Depending on the substrate material, the Langmuir adsorption constants for O3 vary over three orders of magnitude (Kads,O3 ≈ 10−15–10−13 cm3), and the second-order rate coefficients for the surface layer reaction of O3 with different PAH vary over two orders of magnitude (kSLR,PAH,O3 ≈ 10−18–10−17 cm2 s−1). The available data indicate that the Langmuir adsorption constants for NO2 are similar to those of O3, while those of H2O are several orders of magnitude smaller (Kads,H2O ≈ 10−18–10−17 cm3). The desorption lifetimes and adsorption enthalpies inferred from the Langmuir adsorption constants suggest chemisorption of NO2 and O3 and physisorption of H2O. Note, however, that the exact reaction mechanisms, rate limiting steps and possible intermediates still remain to be resolved (e.g., surface diffusion and formation of O atoms or O3− ions at the surface). The K2-SURF model enables the calculation of ozone uptake coefficients, γO3, and of PAH concentrations in the quasi-static particle surface layer. Competitive adsorption and chemical transformation of the surface (aging) lead to a strong non-linear dependence of γO3 on time and gas phase composition, with different characteristics under dilute atmospheric and concentrated laboratory conditions. Under typical ambient conditions, γO3 of PAH-coated aerosol particles are expected to be in the range of 10−6–10−5. At ambient temperatures, NO2 alone does not efficiently degrade PAHs, but it was found to accelerate the degradation of PAHs exposed to O3. The accelerating effect can be attributed to highly reactive NO3 radicals formed in the gas phase or on the surface. Estimated second-order rate coefficients for O3-NO2 and PAH-NO3 surface layer reactions are in the range of 10−17–10−16 cm2 s−1 and 10−15–10−12 cm2 s−1, respectively. The chemical half-life of PAHs is expected to range from a few minutes on the surface of soot to multiple hours on organic and inorganic solid particles and days on liquid particles. On soot, the degradation of particle-bound PAHs in the atmosphere appears to be dominated by a surface layer reaction with adsorbed ozone. On other substrates, it is likely dominated by gas-surface reactions with OH or NO3 radicals (Eley-Rideal-type mechanism). To our knowledge, K2-SURF is the first atmospheric process model describing multiple types of parallel and sequential surface reactions between multiple gaseous and particle-bound chemical species. It illustrates how the general equations of the PRA framework can be simplified and adapted for specific reaction systems, and we suggest that it may serve as a basis for the development of a general master mechanism of aerosol and cloud surface chemistry.

Assessing the Diurnal Cycle of Precipitation in a Multi‐Scale Climate Model

A promising result that has emerged from the new Multi‐scale Modeling Framework (MMF) approach to atmospheric modeling is a global improvement in the daily timing of peak precipitation over the continents, which is suggestive of improved moist dynamics at diurnal timescales overall. We scrutinize the simulated seasonal composite diurnal cycle of precipitation in an MMF developed by the Center for Multiscale Modeling of Atmospheric Processes (CMMAP) using a comprehensive suite of diurnal cycle diagnostics including traditional harmonic analysis, and non‐traditional diagnostics such as the broadness of the peak precipitation in the mean summer day, reduced dimension transect analysis, and animations of the full spatial and temporal variability of the composite mean summer day. Precipitation in the MMF is evaluated against multi‐satellite merged satellite data and a control simulation with a climate model that employs conventional cloud and boundary layer parameterizations. Our analysis highlights several improved features of the diurnal cycle of precipitation in the multi‐scale climate model: It is less sinusoidal over the most energetic diurnal rainfall regimes, more horizontally inhomogeneous within continents and oceans, and more faithful to observed structural transitions in the composite diurnal cycle chronology straddling coastlines than the conventional climate model. A regional focus on North America links a seasonal summer dry bias over the continental United States in the CMMAP MMF at T42 resolution to its inability to capture diurnally propagating precipitation signals associated with organized convection in the lee of the Rockies. The chronology of precipitation events elsewhere in the vicinity of North America is improved in the MMF, especially over sea breeze circulation regions along the eastern seaboard and the Gulf of Mexico, as well as over the entirety of the Gulf Stream. Comparison of the convective heating and moistening suggests that improvements in the MMF coastal ocean diurnal rainfall may be a result of a local moist dynamical response to the improved representation of energetic diurnal forcing over adjacent land.

Post-CCSD(T) ab Initio Thermochemistry of Halogen Oxides and Related Hydrides XOX, XOOX, HOX, XOn, and HXOn (X = F, Cl), and Evaluation of DFT Methods for These Systems

Benchmark-quality W4 (and related) thermochemical data were obtained for the fluorine and chlorine oxides and some related hydrides, all of which are of interest for computational modeling of atmospheric processes. Our best available estimates for total atomization energies at 0 K are the following: HO2 165.97 +/- 0.14, H2O2 252.08 +/- 0.14, HOF 149.24 +/- 0.14, FO 51.17 +/- 0.10, F2O 89.43 +/- 0.14, FO2 130.15 +/- 0.16, F2O2 146.00 +/- 0.16, ClO 63.40 +/- 0.10, HOCl 156.73 +/- 0.14, Cl2O 96.93 +/- 0.16, OClO 122.33 +/- 0.16, ClOO 121.88 +/- 0.32, Cl2O2 142.9 +/- 0.3, ClO3 159.9 +/- 0.4, HClO2 192.0 +/- 0.4, HClO3 258.1 +/- 0.3, and HClO4 313.4 +/- 1 kcal/mol. For several of these species, the total atomization energy contains unusually large components from correlation effects beyond CCSD(T). The geometry of FOOF is significantly affected by connected quadruple excitations. A large variety of DFT exchange-correlation functionals have been evaluated for these systems and observations on their performance are offered. Our best available estimates for deltaHf,0o are the following: HO2 3.65 +/- 0.14, H2O2 -30.82 +/- 0.14, HOF -20.15 +/- 0.14, FO 26.28 +/- 0.11, F2O 6.48 +/- 0.14, FO2 6.30 +/- 0.16, F2O2 8.90 +/- 0.18, ClO 24.19 +/- 0.10, HOCl -17.51 +/- 0.14, Cl2O 19.24 +/- 0.16, OClO 24.26 +/- 0.16, ClOO 24.69 +/- 0.16, Cl2O2 32.3 +/- 0.3, ClO3 45.7 +/- 0.4, HClO2 6.2 +/- 0.4, HClO3 -0.9 +/- 0.3, and HClO4 2.9 +/- 1.0 kcal/mol. (The corresponding values at 298.15 K are 2.96 +/- 0.14, -32.24 +/- 0.14, -20.84 +/- 0.14, 26.43 +/- 0.11, 5.94 +/- 0.14, 5.87 +/- 0.16, 7.84 +/- 0.18, 24.18 +/- 0.10, -18.20 +/- 0.14, 18.82 +/- 0.16, 23.67 +/- 0.16, 24.30 +/- 0.16, 31.5 +/- 0.3, 44.3 +/- 0.4, 5.0 +/- 0.4, -2.6 +/- 0.3, and -0.1 +/- 1.0 kcal/mol, respectively.)

Volume versus surface nucleation in freezing aerosols

The present study puts an end to the ongoing controversy regarding volume versus surface nucleation in freezing aerosols: Our study on nanosized aerosol particles demonstrates that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms. The reasons are inherent experimental uncertainties as well as approximations used to analyze the kinetics. The combination of both can lead to uncertainties in the rate constants of two orders of magnitude, with important consequences for the modeling of atmospheric processes.

Size effects in the catalysis of atmospheric oxidation of SO2 by iron ions

The oxidation of SO2 catalyzed by iron ions in cloud drops of various sizes is analyzed in terms of the reduced model of atmospheric processes. It is demonstrated for the first time that iron ions exert a catalytic effect only in the smallest ( 100 μm) drops. This behavior of iron ions is due to the variation of the concentration ratio between the active form Fe(III) and the inactive form Fe(II) in the drops. SO2 oxidation in drops of intermediate sizes is slower, because most of the iron in these drops is in the Fe(II) state.

Photochemical models of the atmosphere and their application in ozonosphere and climate studies: A review

This review is devoted to problems in the photochemical modeling of atmospheric processes. The physicochemical and mathematical foundations underlying the construction of photochemical models are described, a classification of the atmospheric reactions is presented, and the features of photochemical modeling are considered under various irradiance conditions for various atmospheric layers and geographical regions. Atmospheric processes that are important to photochemical models are discussed. Applications involving photochemical models are outlined. Some results are presented to illustrate the capabilities of photochemical models. Special attention is given to relatively recent directions in photochemical modeling, such as data assimilation and inverse problems. The review can be used by experts in areas related to atmospheric chemistry as a basic source of knowledge on the subject and for the development of photochemical modules for atmospheric models.

Long term atmospheric deposition as the source of nitrate and other salts in the Atacama Desert, Chile: New evidence from mass-independent oxygen isotopic compositions

Isotopic analysis of nitrate and sulfate minerals from the nitrate ore fields of the Atacama Desert in northern Chile has shown anomalous 17O enrichments in both minerals. Δ 17O values of 14–21 ‰ in nitrate and 0.4 to 4 ‰ in sulfate are the most positive found in terrestrial minerals to date. Modeling of atmospheric processes indicates that the Δ 17O signatures are the result of photochemical reactions in the troposphere and stratosphere. We conclude that the bulk of the nitrate, sulfate and other soluble salts in some parts of the Atacama Desert must be the result of atmospheric deposition of particles produced by gas to particle conversion, with minor but varying amounts from sea spray and local terrestrial sources. Flux calculations indicate that the major salt deposits could have accumulated from atmospheric deposition in a period of 200,000 to 2.0 M years during hyper-arid conditions similar to those currently found in the Atacama Desert. Correlations between Δ 17O and δ 18O in nitrate salts from the Atacama Desert and Mojave Desert, California, indicate varying fractions of microbial and photochemical end-member sources. The photochemical nitrate isotope signature is well preserved in the driest surficial environments that are almost lifeless, whereas the microbial nitrate isotope signature becomes dominant rapidly with increasing moisture, biologic activity, and nitrogen cycling. These isotopic signatures have important implications for paleoclimate, astrobiology, and N cycling studies.

On the use of a predictor–corrector scheme to couple the dynamics with the physical parametrizations in the ECMWF model

AbstractMethods of coupling the time integration of the resolved dynamics with the parametrized processes in atmospheric models are an active development area. Many centres have demonstrated strong sensitivity to variations in the methods of coupling in their models. The European Centre for Medium‐Range Weather Forecasts has recently introduced a revised method of coupling which gives significant forecast benefits. Theoretically, optimal methods are difficult to establish because of the mixture of timescales represented within the parametrizations. Implicit methods are well‐suited to achieving coupling between different processes, but are not practical because of the nonlinear switching present in most parametrization schemes. In this paper we show that a predictor–corrector scheme can give some of the advantages of a fully‐implicit scheme. We show that the use of more than one physics evaluation per time step significantly improves the accuracy in a model problem. We also demonstrate the effect of further iterations which, in principle, would converge towards a fully‐implicit scheme. A second iteration has only a small effect on overall performance, but gives a large reduction in the amount of convection. This indicates that the current formulation of convection is not compatible with this type of integration scheme. Copyright © 2003 Royal Meteorological Society

Heterogeneous nucleation of the efflorescence of (NH4)2SO4 particles internally mixed with Al2O3, TiO2, and ZrO2

Accurate models of atmospheric processes are currently hindered by poor microphysical models of particle phase transitions, including efflorescence. For aqueous particles, it is possible that insoluble crustal inclusions behave as heterogeneous nuclei to induce efflorescence. This paper reports on the results of laboratory experiments concerning the efflorescence of (NH4)2SO4 particles that are internally mixed with TiO2, Al2O3, or ZrO2 particles. The particles are prepared by condensing SO3 and H2O vapors in the presence of insoluble metal oxide particles, followed by neutralization with NH3. A Fourier transform infrared spectrometer is employed to observe the aqueous‐to‐solid phase change as relative humidity decreases. Efflorescence occurs at 35% relative humidity (±2%) in the absence of heterogeneous nuclei. In contrast, internally mixed particles effloresce at 57% (Al2O3), 59% (ZrO2), and 65% (TiO2) at 298 K.

Dynamic probabilistic model of atmospheric processes and the variational methods of data assimilation

Dynamic probabilistic model of atmospheric processes and the variational methods of data assimilation

Multiscale modeling of spatially variable water and energy balance processes

This paper presents the model development component of a body of research which addresses aggregation and scaling in multiscale hydrological modeling. Water and energy balance models are developed at the local and catchment scales and at the macroscale by aggregating a simple soil‐vegetation‐atmosphere transfer scheme (SVATS) across scales in a topographic framework. A spatially distributed approach is followed to aggregate the SVATS to the catchment scale. A statistical‐dynamical approach is utilized to simplify the large‐scale modeling problem and to aggregate the SVATS to the macroscale. The resulting macroscale hydrological model is proposed for use as a land surface parameterization in atmospheric models. It differs greatly from the current generation of land surface parameterizations owing to its simplified representation of vertical process physics and its statistical representation of horizontally heterogeneous runoff and energy balance processes. The spatially distributed model formulation is explored to understand the role of spatial variability in determining areal‐average fluxes and the dynamics of hydrological processes. The simpler macroscale formulation is analyzed to determine how it represents these important dynamics, with implications for the parameterization of runoff and energy balance processes in atmospheric models.

Over-ocean atmospheric boundary layer dynamics under varying wind-wave development stage

Dynamic characteristics of the over-ocean atmospheric planetary boundary layer are obtained for a given geostrophic wind velocity and for varying wind-wave age, which depends on time and on varying near-water wind. Numerical experiments are done with use of a theoretical atmospheric boundary layer model and of a stochastic dependence of the non-dimensional sea surface roughness length on the wave age criterion. It is found that wind-wave development stage visibly influences the dynamic structure of the atmospheric boundary layer. So the wave age must be taken into account in analysing and modeling of atmospheric processes in the vicinity of frontal zones, in areas of intense cyclone activity etc. The discussed influence is important first of all in problems of synotic or of shorter time scales.

Radiation and cloud processes in the atmosphere: theory, observation, and modeling

Introduction Theory and parameterization of thermal infrared radiative transfer Theory and parameterization of solar radiation transfer Theory, observation and modeling of cloud processes in the atmosphere Radiative transfer in clouds Atmospheres in radiative and thermal equilibrium The role of radiation and cloud processes in atmospheric models Appendices: Physical constants Standard atmospheric profiles Complex refractive indices of water and ice.

Physical processes in atmospheric models. Edited by D. R. Sikka and S. S. Singh. Wiley Eastern, 1992. Pp. 586

Physical processes in atmospheric models. Edited by D. R. Sikka and S. S. Singh. Wiley Eastern, 1992. Pp. 586

Conceptual aspects of a statistical‐dynamical approach to represent landscape subgrid‐scale heterogeneities in atmospheric models

Land‐surface characteristics play a key role in the partition of energy received at the Earth's surface and, as a result, have a major impact on the atmosphere. Yet the representation of land‐surface processes in atmospheric models is not realistic. Actual state‐of‐the‐art parameterizations of land surfaces do not account for the landscape heterogeneity found on the resolvable scale of these models and are based on a large amount of empirical constants that in practice can be difficult to estimate. An alternative parameterization based on a statistical‐dynamical approach is suggested here. With this approach, the most important characteristics of the soil‐plant‐atmosphere system that affect the partition of energy (e.g., plant stomatal conductance, soil humidity, surface roughness) would be represented by a probability density function (pdf) rather than by a single “representative” value. Typically, such pdf's are characterized by two to four parameters. A primary simplified version of this parameterization was used to estimate the land‐surface energy fluxes that are produced at the grid scale by various distributions of stomatal conductance under a broad range of environmental conditions. To demonstrate the potential of the approach, results were compared with the same fluxes calculated with a big leaf model using the mean stomatal conductance that corresponds to the distributions. Large absolute and relative differences are obtained between the two schemes for many combinations of stomatal conductance pdf's and environmental conditions. These differences are due mainly to the nonlinearity of the processes involved in the redistribution of the energy absorbed at the ground surface. These numerical experiments demonstrate the importance of accounting for landscape heterogeneity in the simulation of land‐surface energy fluxes, and demonstrate the potential benefits of adopting a statistical‐dynamical approach for the representation of land‐surface processes in atmospheric models.

Evidence of a chaotic attractor in star-wander data

The observed motion of stellar-image centroids is shown to have a chaotic attractor with a correlation dimension of ~6. The existence of a chaotic attractor in star wander, or equivalently in wave-front tilts, indicates that the atmospheric processes that cause image degradation may be more accurately described as chaotic, not so random as is usually assumed. This new result has important implications for the accurate modeling of atmospheric processes, the operation of adaptive optics systems, and the processing of stellar images.

The representation of continental surface processes in atmospheric models

This paper provides a general overview of the issues related to the modeling of surface processes in atmospheric models. The role of surface processes is first discussed as an essential coupling between the surface and the atmosphere. The issue of parameterization of small‐scale processes in large‐scale atmospheric models is addressed next, paying special attention to the cases of bare ground and vegetated surfaces. The paper focuses on the issues rather than the details of implementation, and extensive citations to the published literature are given for further investigations.

Solar and Terrestrial Radiation: Methods and Measurements

This will be a welcome contribution for students and research workers in the fields of meteorology and solar radiation physics. While it provides basic background to the subject (the radiation transmission absorption and scattering mechanisms along with treatments of current models of atmospheric processes) the major value of the work is in its detailed explanation of the construction and principles of operation of the many measuring instruments in current use.

Research program for assessment of stratospheric pollution

This is a review of a United States Department of Transportation program to determine the regulatory constraints necessary to safeguard that future flights in the stratosphere do not result in adverse environmental effects. The program, called the Climatic Impact Assessment Program (CIAP), considers the impact on people, plants, and animals of climatic changes resulting from perturbing the upper atmosphere by the propulsion effluents of a world high-altitude fleet as projected to 1990. The program is to provide a report by December 1974 on the impact of climatic changes which will take into account both socioeconomic concerns and the possibility of applying technology and regulations to alleviate those concerns. CIAP's initial output is a set of six monographs which are compilations of data in the areas suggested by their titles: The Natural Stratosphere, The Engine Emissions in the Stratosphere of 1990 A.D., The Perturbed Stratosphere of 1990 A.D., The Perturbed Troposphere of 1990 and 2020 A.D., The Biological Effects of the Tropospheric Changes, and The Social and Cost Measures of the Biological Changes. The conclusions of CIAP will appear in the Report of Findings, to be published in December 1974, which will draw upon the data presented in the monographs. The physical science concerns of CIAP center on: (1) possible depletions of ozone as a result of interactions between engine exhaust emissions and naturally present stratospheric constituents; (2) consequent changes in ultraviolet reaching the earth's surface as a result of ozone depletion; (3) possible changes in heating at the earth's surface caused by the formation of stratospheric aerosols from aircraft emissions or by the injection of carbon dioxide and water vapor into the stratosphere from aircraft emissions. Biological and economic concerns of CIAP have to do with changes in agricultural, forest and marine productivity or effects on human health and their economic consequences. CIAP also takes into account the need for theoretical modeling of atmospheric processes, projections of stratospheric aircraft fleet size and traffic, the development of programs to ascertain that predicted impacts are verified, and the development of regulatory programs to control total stratospheric emissions.