The impact of inhomogeneous emissions and topography on ozone photochemistry in the vicinity of the Hong Kong island

Abstract. Global and regional chemical transport models of the atmosphere are based on the assumption that chemical species are completely mixed within each model grid box. However, in reality, these species are often segregated due to localized sources and the influence of the topography. In order to investigate the degree to which the rates of chemical reactions between two reactive species are reduced due to the possible segregation of species within the convective boundary layer, we perform large-eddy simulations (LES) in the mountainous region of the Hong Kong island. We adopt a simple chemical scheme with 15 primary and secondary chemical species including ozone and its precursors. We calculate the segregation intensity due to inhomogeneity in the surface emissions of primary pollutants and due to turbulent motions related to topography. We show that the inhomogeneity in the emissions increases the segregation intensity by a factor 2–5 relative to a case in which the emissions are assumed to be uniformly distributed. Topography has an important effect on the segregation locally, but this influence is relatively limited when considering the spatial domain as a whole.

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The impact of inhomogeneous emissions and topography on ozone photochemistry in the vicinity of Hong Kong Island

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-3531-2021 ◽

2021 ◽

Vol 21 (5) ◽

pp. 3531-3553

Author(s):

Yuting Wang ◽

Yong-Feng Ma ◽

Domingo Muñoz-Esparza ◽

Cathy W. Y. Li ◽

Mary Barth ◽

...

Keyword(s):

Hong Kong ◽

Surface Ozone ◽

Chemical Species ◽

Convective Boundary ◽

Large Eddy ◽

Segregation Effect ◽

Chemical Scheme ◽

Ozone Photochemistry ◽

The Impact ◽

Secondary Chemical

Abstract. Global and regional chemical transport models of the atmosphere are based on the assumption that chemical species are completely mixed within each model grid box. However, in reality, these species are often segregated due to localized sources and the influence of topography. In order to investigate the degree to which the rates of chemical reactions between two reactive species are reduced due to the possible segregation of species within the convective boundary layer, we perform large-eddy simulations (LESs) in the mountainous region of Hong Kong Island. We adopt a simple chemical scheme with 15 primary and secondary chemical species, including ozone and its precursors. We calculate the segregation intensity due to inhomogeneity in the surface emissions of primary pollutants and due to turbulent motions related to topography. We show that the inhomogeneity in the emissions increases the segregation intensity by a factor of 2–5 relative to a case in which the emissions are assumed to be uniformly distributed. Topography has an important effect on the segregation locally, but this influence is relatively limited when considering the spatial domain as a whole. In the particular setting of our model, segregation reduces the ozone formation by 8 %–12 % compared to the case with complete mixing, implying that the coarse-resolution models may overestimate the surface ozone when ignoring the segregation effect.

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Implications of Nonlocal Transport and Conditionally Averaged Statistics on Monin–Obukhov Similarity Theory and Townsend’s Attached Eddy Hypothesis

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-17-0301.1 ◽

2018 ◽

Vol 75 (10) ◽

pp. 3403-3431 ◽

Cited By ~ 12

Author(s):

Qi Li ◽

Pierre Gentine ◽

Juan Pedro Mellado ◽

Kaighin A. McColl

Keyword(s):

Similarity Theory ◽

Turbulent Transport ◽

Strong Interactions ◽

Similarity Function ◽

Convective Boundary ◽

Structure Detection ◽

Large Eddy ◽

Attached Eddies ◽

The Impact

According to Townsend’s hypothesis, so-called wall-attached eddies are the main contributors to turbulent transport in the atmospheric surface layer (ASL). This is also one of the main assumptions of Monin–Obukhov similarity theory (MOST). However, previous evidence seems to indicate that outer-scale eddies can impact the ASL, resulting in deviations from the classic MOST scaling. We conduct large-eddy simulations and direct numerical simulations of a dry convective boundary layer to investigate the impact of coherent structures on the ASL. A height-dependent passive tracer enables coherent structure detection and conditional analysis based on updrafts and subsidence. The MOST similarity functions computed from the simulation results indicate a larger deviation of the momentum similarity function ϕ m from classical scaling relationships compared to the temperature similarity function ϕ h. The conditional-averaged ϕ m for updrafts and subsidence are similar, indicating strong interactions between the inner and outer layers. However, ϕ h conditioned on subsidence follows the mixed-layer scaling, while its updraft counterpart is well predicted by MOST. Updrafts are the dominant contributors to the transport of momentum and temperature. Subsidence, which comprises eddies that originate from the outer layer, contributes increasingly to the transport of temperature with increasing instability. However, u′ of different signs are distributed symmetrically in subsidence unlike the predominantly negative θ′ as instability increases. Thus, the spatial patterns of u′ w′ differ compared to θ′ w′ in regions of subsidence. These results depict the mechanisms for departure from the MOST scaling, which is related to the stronger role of subsidence.

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Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-9335-2012 ◽

2012 ◽

Vol 12 (19) ◽

pp. 9335-9353 ◽

Cited By ~ 30

Author(s):

H. G. Ouwersloot ◽

J. Vilà-Guerau de Arellano ◽

A. C. Nölscher ◽

M. C. Krol ◽

L. N. Ganzeveld ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Chemistry ◽

Convective Boundary Layer ◽

Large Scale ◽

Spatial Scales ◽

Potential Temperature ◽

Chemical Species ◽

Convective Boundary ◽

The Impact

Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day, focusing on the convective boundary layer, to analyse the influence of the dynamics on the chemical evolution of the ABL. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.

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Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-13619-2012 ◽

2012 ◽

Vol 12 (6) ◽

pp. 13619-13665 ◽

Cited By ~ 2

Author(s):

H. G. Ouwersloot ◽

J. Vilà-Guerau de Arellano ◽

A. C. Nölscher ◽

M. C. Krol ◽

L. N. Ganzeveld ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Chemistry ◽

Convective Boundary Layer ◽

Large Scale ◽

Spatial Scales ◽

Potential Temperature ◽

Chemical Species ◽

Convective Boundary ◽

Systematic Analysis ◽

The Impact

Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day characterized as a convective boundary layer to analyse the influence of the dynamics on the chemical evolution of the ABL, using a systematic analysis that can easily be extended to other periods during HUMPPA-COPEC-2010. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.

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Recent Advances in Speciation Analyses of Tobacco and Other Important Economic Crops

Current Analytical Chemistry ◽

10.2174/1573411017999201201115234 ◽

2020 ◽

Vol 17 ◽

Author(s):

Zhiping Jiang ◽

Zhizhang Tian ◽

Chuntao Zhang ◽

Dengke Li ◽

Ruoxin Wu ◽

...

Keyword(s):

Method Comparison ◽

Chemical Species ◽

Complete Information ◽

Speciation Analysis ◽

Elemental Content ◽

Specific Element ◽

Balance Accuracy ◽

Comprehensive Knowledge ◽

Total Elemental Content ◽

The Impact

Background: Speciation analysis is defined as the analytical activities of identifying and/or measuring the quantities of one or more individual chemical species in a sample. The knowledge of elemental species provides more complete information about mobility, bioavailability and the impact of elements on ecological systems or biological organisms. It is no longer sufficient to quantitate the total elemental content of samples to define toxicity or essentiality. Thus speciation analysis is of vital importance and generally offers a better understanding of a specific element. Discussion: Thorough speciation scheme consisting of sampling, sample preparation, species analysis and evaluation were described. Special emphasis is placed on recent speciation analysis approaches including both direct and coupling methods. A current summary of advantages and limitations of the various methods as well as an illustrative method comparison are presented. Certain elements and species of interest are briefly mentioned and practical examples of speciation applications in tobacco and other important economic crops are also discussed. Aim/Conclusion: This review aims to offer comprehensive knowledge about elemental speciation and provide readers with valuable information. Many strategies have been developed for the determination of multiple elemental species in tobacco and other important economic crops. Nevertheless, it is an eternal pursuit to establish speciation methods which can balance accuracy, agility as well as universality.

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Shock interactions in inviscid air and $$\hbox {CO}_2$$–$$\hbox {N}_2$$ flows in thermochemical non-equilibrium

Shock Waves ◽

10.1007/s00193-021-00999-8 ◽

2021 ◽

Author(s):

C. Garbacz ◽

W. T. Maier ◽

J. B. Scoggins ◽

T. D. Economon ◽

T. Magin ◽

...

Keyword(s):

Chemical Species ◽

High Energy ◽

Ideal Gas ◽

Shock Interaction ◽

Interaction Patterns ◽

Shock Interactions ◽

Wave Interference ◽

Type V ◽

The Impact ◽

Non Equilibrium

AbstractThe present study aims at providing insights into shock wave interference patterns in gas flows when a mixture different than air is considered. High-energy non-equilibrium flows of air and $$\hbox {CO}_2$$ CO 2 –$$\hbox {N}_2$$ N 2 over a double-wedge geometry are studied numerically. The impact of freestream temperature on the non-equilibrium shock interaction patterns is investigated by simulating two different sets of freestream conditions. To this purpose, the SU2 solver has been extended to account for the conservation of chemical species as well as multiple energies and coupled to the Mutation++ library (Multicomponent Thermodynamic And Transport properties for IONized gases in C++) that provides all the necessary thermochemical properties of the mixture and chemical species. An analysis of the shock interference patterns is presented with respect to the existing taxonomy of interactions. A comparison between calorically perfect ideal gas and non-equilibrium simulations confirms that non-equilibrium effects greatly influence the shock interaction patterns. When thermochemical relaxation is considered, a type VI interaction is obtained for the $$\hbox {CO}_2$$ CO 2 -dominated flow, for both freestream temperatures of 300 K and 1000 K; for air, a type V six-shock interaction and a type VI interaction are obtained, respectively. We conclude that the increase in freestream temperature has a large impact on the shock interaction pattern of the air flow, whereas for the $$\hbox {CO}_2$$ CO 2 –$$\hbox {N}_2$$ N 2 flow the pattern does not change.

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Share Contract Revisited: A New Transaction Cost Approach

Man and the Economy ◽

10.1515/me-2021-0001 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Jian Ding ◽

Yixiao Zhou

Keyword(s):

Hong Kong ◽

Transaction Cost ◽

Empirical Studies ◽

Theoretical Explanation ◽

Empirical Testing ◽

Cost Approach ◽

Satisfactory Answer ◽

The Impact

Abstract The purpose of this paper is to explore how sharecropping contracts are chosen over fixed-rent contracts. There are two concerning issues. First, theoretical explanation has been criticized for not providing a satisfactory answer to the question as to why share contracts are chosen. Second, among the existing empirical studies, there are great controversies about the impact of variance of output. Inspired by the latest insights from (Cheung, S. N. S. 2014. Economic Explanation. Hong Kong: Arcadia Press.), this paper not only provides an explanation for the choice of share contract that is suitable for empirical testing, but also solves the puzzle over variance of output.

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