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Atmosphere, Volume 8, Issue 9 (September 2017)

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Cover Story Sampling on different substrates is common in aerosol research. In our study, collected particles [...] Read more.
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Open AccessArticle Unstable Leader Inception Criteria of Atmospheric Discharges
Atmosphere 2017, 8(9), 156; doi:10.3390/atmos8090156
Received: 29 May 2017 / Revised: 19 August 2017 / Accepted: 21 August 2017 / Published: 23 August 2017
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Abstract
In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for
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In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for the minimum amount of electrical charge required to incept an unstable leader has recently been used for modeling long gap discharges and lightning attachments. The criterion is based on the assumption that the total energy of the streamer is used to heat up the gas, among other principles. However, from a physics point of view, energy can also be transferred to other molecular processes, such as rotation, translation, and vibrational excitation. In this paper, the leader inception mechanism was studied based on fundamental particle physics and the energy balance of the gas media. The heating process of the plasma is evaluated with a detailed two-dimensional self-consistent model. The model is able to represent the streamer propagation, dark period, and unsuccessful leaders that may occur prior to the heating of the channel. The main processes that participate in heating the gas are identified within the model, indicating that impact ionization and detachment are the leading sources of energy injection, and that recombination is responsible for loss of electrons and limiting the energy. The model was applied to a well-known experiment for long air gaps under positive switching impulses reported in the literature, and used to validate models for lightning attachments and long gap discharges. Results indicate that the streamer–leader transition depends on the amount of energy transferred to the heating process. The minimum electric charge required for leader inception varies with the gap geometry, the background electric field, the reduction of electric field due to the space charge, the energy expended on the vibrational relation, and the environmental conditions, among others. Full article
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Open AccessArticle The Impact of Residential Combustion Emissions on Health Expenditures: Empirical Evidence from Sub-Saharan Africa
Atmosphere 2017, 8(9), 157; doi:10.3390/atmos8090157
Received: 6 July 2017 / Revised: 17 August 2017 / Accepted: 22 August 2017 / Published: 25 August 2017
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Abstract
Residential combustion of fuels, especially solid, for cooking, heating and other activities generates high level emissions that considerably contribute to indoor and outdoor air pollutants concentrations, which adversely affect human health and are likely to influence heath expenditures. We used the system General
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Residential combustion of fuels, especially solid, for cooking, heating and other activities generates high level emissions that considerably contribute to indoor and outdoor air pollutants concentrations, which adversely affect human health and are likely to influence heath expenditures. We used the system General Method of Moments (GMM) technique to examine the role of residential combustion (proxied by: particulate matter (PM2.5), carbon monoxide (CO), nitrogen oxide (NOx) and sulphur dioxide (SO2) emissions) in determining health expenditures while controlling for ambient air pollutants emissions from the other categories such as transportation, manufacturing industries and construction, and others. We employed data covering the period 1995–2010 in 44 countries of Sub-Saharan Africa (SSA). Health expenditures are categorized into per capita, public and private out-of-pocket; and we run three separate regressions according to the categories. The findings indicate that residential sector combustion was significantly associated with higher health expenditures, especially the out-of-pocket compared with other categories. Moreover, PM2.5 is found to have the highest impact on health expenditures. The implementation of effective public health and environmental health policies that encourage the access and use of cleaner fuels or improved cook stoves in SSA would be associated with not only a reduction in healthcare expenditures but also with other health and socio-economic benefits. Full article
(This article belongs to the Special Issue Indoor Air Pollution)
Open AccessArticle Origins of Moist Air in Global Lagrangian Simulations of the Madden–Julian Oscillation
Atmosphere 2017, 8(9), 158; doi:10.3390/atmos8090158
Received: 20 May 2017 / Revised: 14 August 2017 / Accepted: 16 August 2017 / Published: 26 August 2017
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Abstract
Many recent studies have characterized the Madden–Julian Oscillation (MJO) as a moisture mode, suggesting that its amplification and eastward propagation result from processes that build up moisture to the east of the MJO’s convective center, including frictionally driven boundary layer convergence, surface fluxes,
[...] Read more.
Many recent studies have characterized the Madden–Julian Oscillation (MJO) as a moisture mode, suggesting that its amplification and eastward propagation result from processes that build up moisture to the east of the MJO’s convective center, including frictionally driven boundary layer convergence, surface fluxes, and shallow convection. Discussions of MJO moistening under this theory often implicitly assume an Eulerian framework; i.e., that local increases in moisture result from physical processes acting in the same location as the moistening is observed. In this study, the authors examine MJO moistening in a Lagrangian framework using a model that simulates atmospheric circulations by predicting the motions of individual air parcels. Back trajectories are presented for parcels in moist convecting regions of the MJO, and the effects of different physical processes on their moisture and moist static energy budgets are quantified. The Lagrangian MJO simulations suggest that much of the low-level moist air in heavily precipitating regions of the MJO arrives via the mid troposphere, coming from nearby equatorial regions, where it has been moistened largely by convective processes. Consequently, a thorough understanding of MJO moistening requires knowledge of the origin of the moist air and information about remote moisture sources. Full article
(This article belongs to the Special Issue Madden-Julian Oscillation)
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Open AccessArticle Pedestrian-Level Urban Wind Flow Enhancement with Wind Catchers
Atmosphere 2017, 8(9), 159; doi:10.3390/atmos8090159
Received: 10 July 2017 / Revised: 3 August 2017 / Accepted: 22 August 2017 / Published: 25 August 2017
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Abstract
Dense urban areas restrict air movement, causing airflow in urban street canyons to be much lower than the flow above buildings. Boosting near-ground wind speed can enhance thermal comfort in warm climates by increasing skin convective heat transfer. We explored the potential of
[...] Read more.
Dense urban areas restrict air movement, causing airflow in urban street canyons to be much lower than the flow above buildings. Boosting near-ground wind speed can enhance thermal comfort in warm climates by increasing skin convective heat transfer. We explored the potential of a wind catcher to direct atmospheric wind into urban street canyons. We arranged scaled-down models of buildings with a wind catcher prototype in a water channel to simulate flow across two-dimensional urban street canyons. Velocity profiles were measured with Acoustic Doppler Velocimeters. Experiments showed that a wind catcher enhances pedestrian-level wind speed in the target canyon by 2.5 times. The flow enhancement is local to the target canyon with little effect in other canyons. With reversed flow direction, a “reversed wind catcher” has no effect in the target canyon but reduces the flow in the immediate downstream canyon. The reversed wind catcher exhibits a similar blockage effect of a tall building amid an array of lower buildings. Next, we validated Computational Fluid Dynamics (CFD) simulations of all cases with experiments and extended the study to reveal impacts on three-dimensional ensembles of buildings. A wind catcher with closed sidewalls enhances maximum pedestrian-level wind speed in three-dimensional canyons by four times. Our results encourage better designs of wind catchers to increase wind speed in targeted areas. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Spatial Distributions of Tropical Cyclone Tornadoes by Intensity and Size Characteristics
Atmosphere 2017, 8(9), 160; doi:10.3390/atmos8090160
Received: 9 August 2017 / Revised: 22 August 2017 / Accepted: 25 August 2017 / Published: 28 August 2017
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Abstract
Tropical cyclones that make landfall often spawn tornadoes. Previous studies have shown that these tornadoes are not uniformly distributed in the United States or in the tropical cyclone environment. They show that tornadoes tend to occur relatively close to the coastline and that
[...] Read more.
Tropical cyclones that make landfall often spawn tornadoes. Previous studies have shown that these tornadoes are not uniformly distributed in the United States or in the tropical cyclone environment. They show that tornadoes tend to occur relatively close to the coastline and that they tend to cluster to the east-of-center in the tropical cyclone environment, particularly in the northeast and east-of-center quadrants. This study contributes to these studies by analyzing the spatial distributions of tropical cyclone tornadoes by intensity, path length, path width, and the damage potential index. The analyses confirm that most tornadoes occur relatively close to the coastline, but show that stronger tornadoes with larger paths are disproportionately common farther inland. They also confirm that the highest amount of activity is located within the northeast and east-of-center quadrants and show that the most potentially damaging tornadoes cluster in a sub region near the intersection of these two quadrants. Full article
(This article belongs to the Special Issue Tropical Cyclones and Their Impacts)
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Open AccessArticle Comparing CMAQ Forecasts with a Neural Network Forecast Model for PM2.5 in New York
Atmosphere 2017, 8(9), 161; doi:10.3390/atmos8090161
Received: 30 June 2017 / Revised: 22 August 2017 / Accepted: 26 August 2017 / Published: 29 August 2017
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Abstract
Human health is strongly affected by the concentration of fine particulate matter (PM2.5). The need to forecast unhealthy conditions has driven the development of Chemical Transport Models such as Community Multi-Scale Air Quality (CMAQ). These models attempt to simulate the complex
[...] Read more.
Human health is strongly affected by the concentration of fine particulate matter (PM2.5). The need to forecast unhealthy conditions has driven the development of Chemical Transport Models such as Community Multi-Scale Air Quality (CMAQ). These models attempt to simulate the complex dynamics of chemical transport by combined meteorology, emission inventories (EI’s), and gas/particle chemistry and dynamics. Ultimately, the goal is to establish useful forecasts that could provide vulnerable members of the population with warnings. In the simplest utilization, any forecast should focus on next day pollution levels, and should be provided by the end of the business day (5 p.m. local). This paper explores the potential of different approaches in providing these forecasts. First, we assess the potential of CMAQ forecasts at the single grid cell level (12 km), and show that significant variability not encountered in the field measurements occurs. This observation motivates the exploration of other data driven approaches, in particular, a neural network (NN) approach. This approach makes use of meteorology and PM2.5 observations as model predictors. We find that this approach generally results in a more accurate prediction of future pollution levels at the 12 km spatial resolution scale of CMAQ. Furthermore, we find that the NN is able to adjust to the sharp transitions encountered in pollution transported events, such as smoke plumes from forest fires, more accurately than CMAQ. Full article
(This article belongs to the Special Issue Air Quality Monitoring and Forecasting)
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Open AccessArticle The Impact of Sampling Medium and Environment on Particle Morphology
Atmosphere 2017, 8(9), 162; doi:10.3390/atmos8090162
Received: 23 July 2017 / Revised: 25 August 2017 / Accepted: 26 August 2017 / Published: 29 August 2017
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Abstract
Sampling on different substrates is commonly used in laboratory and field studies to investigate the morphology and mixing state of aerosol particles. Our focus was on the transformations that can occur to the collected particles during storage, handling, and analysis. Particle samples were
[...] Read more.
Sampling on different substrates is commonly used in laboratory and field studies to investigate the morphology and mixing state of aerosol particles. Our focus was on the transformations that can occur to the collected particles during storage, handling, and analysis. Particle samples were prepared by electrostatic deposition of size-classified sodium chloride, sulfuric acid, and coated soot aerosols on different substrates. The samples were inspected by electron microscopy before and after exposure to various environments. For coated soot, the imaging results were compared against mass-mobility measurements of airborne particles that underwent similar treatments. The extent of sample alteration ranged from negligible to major, depending on the environment, substrate, and particle composition. We discussed the implications of our findings for cases where morphology and the mixing state of particles must be preserved, and cases where particle transformations are desirable. Full article
(This article belongs to the Special Issue Morphology and Internal Mixing of Atmospheric Particles)
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Open AccessArticle Numerical Study on the Urban Ventilation in Regulating Microclimate and Pollutant Dispersion in Urban Street Canyon: A Case Study of Nanjing New Region, China
Atmosphere 2017, 8(9), 164; doi:10.3390/atmos8090164
Received: 30 July 2017 / Revised: 26 August 2017 / Accepted: 26 August 2017 / Published: 29 August 2017
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Abstract
Urban ventilation plays an important role in regulating city climate and air quality. A numerical study was conducted to explore the ventilation effectiveness on the microclimate and pollutant removal in the urban street canyon based on the rebuilt Southern New Town region in
[...] Read more.
Urban ventilation plays an important role in regulating city climate and air quality. A numerical study was conducted to explore the ventilation effectiveness on the microclimate and pollutant removal in the urban street canyon based on the rebuilt Southern New Town region in Nanjing, China. The RNG k ε turbulence model in the computational fluid dynamics (CFD) was employed to study the street canyon under parallel and perpendicular wind directions, respectively. Velocity inside of the street canyon and temperature on the building envelopes were obtained. A novel pressure coefficient was defined, and three methods were applied to evaluate the urban ventilation effectiveness. Results revealed that there was little comfort difference for the human body under two ventilation patterns in the street canyon. Air stagnation occurred easily in dense building clusters, especially under the perpendicular wind direction. In addition, large pressure coefficients ( C P > 1 ) appeared at the windward region, contributing to promising ventilation. The air age was introduced to evaluate the “freshness” of the air in the street canyon and illustrated the ventilation effectiveness on the pollutant removal. It was found that the young air distributed where the corresponding ventilation was favorable and the wind speed was large. The results from this study can be useful in further city renovation for the street canyon construction and municipal planning. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Comparing the Spatial Patterns of Rainfall and Atmospheric Moisture among Tropical Cyclones Having a Track Similar to Hurricane Irene (2011)
Atmosphere 2017, 8(9), 165; doi:10.3390/atmos8090165
Received: 26 July 2017 / Revised: 19 August 2017 / Accepted: 1 September 2017 / Published: 6 September 2017
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Abstract
Irene was the most destructive tropical cyclone (TC) of the 2011 Atlantic hurricane season due to flooding from rainfall. This study used a Geographic Information System to identify TCs with similar tracks and examine the spatial attributes of their rainfall patterns. Storm-total rainfall
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Irene was the most destructive tropical cyclone (TC) of the 2011 Atlantic hurricane season due to flooding from rainfall. This study used a Geographic Information System to identify TCs with similar tracks and examine the spatial attributes of their rainfall patterns. Storm-total rainfall was calculated from the Unified Precipitation Dataset for 11 post-1948 storms and statistics corresponding to the top 10% of rainfall values left of track were computed. Irene-type tracks occur every 6.6 years. Floyd (1999) produced the highest rainfall overall and was the closest analog to Irene, yet Irene produced more rainfall in the northeastern U.S. where higher values of precipitable water existed. Areas of high rainfall expanded as five TCs moved north due to synoptic-scale forcing during extratropical transition. However, Irene and three other TCs did not exhibit this pattern. The amount of moisture in the environment surrounding the TC, rather than storm speed or intensity, exhibited the strongest correlations with rainfall totals and their spatial distribution. These results demonstrate the high variability that exists in the production of rainfall among TCs experiencing similar steering flow, and show that advection of moisture from the tropics is key to higher rainfall totals in the mid-latitudes. Full article
(This article belongs to the Special Issue Tropical Cyclones and Their Impacts)
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Open AccessArticle Effect of Thermodenuding on the Structure of Nascent Flame Soot Aggregates
Atmosphere 2017, 8(9), 166; doi:10.3390/atmos8090166
Received: 27 July 2017 / Revised: 29 August 2017 / Accepted: 31 August 2017 / Published: 6 September 2017
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Abstract
The optical properties (absorption and scattering) of soot particles depend on soot size and index of refraction, but also on the soot complex morphology and the internal mixing with materials that can condense on a freshly emitted (nascent) soot particle and coat it.
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The optical properties (absorption and scattering) of soot particles depend on soot size and index of refraction, but also on the soot complex morphology and the internal mixing with materials that can condense on a freshly emitted (nascent) soot particle and coat it. This coating can affect the soot optical properties by refracting light, or by changing the soot aggregate structure. A common approach to studying the effect of coating on soot optical properties is to measure the absorption and scattering coefficients in ambient air, and then measure them again after removing the coating using a thermodenuder. In this approach, it is assumed that: (1) most of the coating material is removed; (2) charred organic coating does not add to the refractory carbon; (3) oxidation of soot is negligible; and, (4) the structure of the pre-existing soot core is left unaltered, despite the potential oxidation of the core at elevated temperatures. In this study, we investigated the validity of the last assumption, by studying the effect of thermodenuding on the morphology of nascent soot. To this end, we analyzed the morphological properties of laboratory generated nascent soot, before and after thermodenuding. Our investigation shows that there is only minor restructuring of nascent soot by thermodenuding. Full article
(This article belongs to the Special Issue Morphology and Internal Mixing of Atmospheric Particles)
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Open AccessArticle Emission Inventory of On-Road Transport in Bangkok Metropolitan Region (BMR) Development during 2007 to 2015 Using the GAINS Model
Atmosphere 2017, 8(9), 167; doi:10.3390/atmos8090167
Received: 9 August 2017 / Revised: 30 August 2017 / Accepted: 5 September 2017 / Published: 7 September 2017
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Abstract
Bangkok Metropolitan Region (BMR), including the capital city and five adjacent provinces, constitutes one of the top 10 megacities experiencing serious traffic congestion in the world, leading to air quality problems with significant adverse human health risks. Previously, there have been many operations
[...] Read more.
Bangkok Metropolitan Region (BMR), including the capital city and five adjacent provinces, constitutes one of the top 10 megacities experiencing serious traffic congestion in the world, leading to air quality problems with significant adverse human health risks. Previously, there have been many operations planned to influence the fuel consumption and emissions from the on-road transport sector in the BMR area. It is necessary to estimate emissions using detailed information in order to thoroughly understand the reason for changes in emission levels and their impact on air quality. This paper aims to determine the successful implementation of energy and air pollution control policies in Thailand through an investigation of the emissions inventory of on-road transport in BMR, including ozone precursors (CO, NOX, Non-methane volatile organic compounds (NMVOCs) ), greenhouse gases (CO2, CH4, N2O), acidic substances (SO2 and NH3), and particulate matters (PM2.5, PM10, Black Carbon (BC), Organic Carbon (OC)) during the period from 2007 to 2015, using the Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS) model based on the country-specific activity data together with the emission factor from the GAINS-Asia database. This study found that the amount of exhaust emissions over the BMR area in the year 2015 (and the trend during the period from 2007 to 2015) is approximately 139 kt of CO (−7.9%), 103 kt of NOX (−4.1%), 19.9 kt of NMVOC (−6.7%), 15 kt of CO2 (+1.6%), 8.6 kt of CH4 (+6.8%), 0.59 kt of N2O (+1.3%), 0.87 kt of SO2 (−25.8%), 1.1 kt of NH3 (+7.8%), 4.9 kt of PM2.5 (−5.5%), 5.1 kt of PM10 (−7.9%), 3.1 kt of BC (−2.5%), and 1.4 kt of OC (−7.7%). The change in emissions in each pollutant is a result of the more stringent control of fuel and engine standards, the shift in the fuel type used, and the effects of controlling some emissions. Light duty car gasoline fuel is identified as a major contributor of CO, NH3, N2O, and NMVOC, whereas trucks are the greatest emitters of NOX, SO2, and particulate matter. This study suggests that the most powerful implementation plan for the continuous, significant reduction of ozone precursor, SO2, and particulate matter emissions is the more stringent enforcement of fuel and vehicle standard levels, especially concerning light duty vehicles. Full article
(This article belongs to the Special Issue Urban Air Pollution)
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Open AccessArticle Effects of Unstable Stratification on Ventilation in Hong Kong
Atmosphere 2017, 8(9), 168; doi:10.3390/atmos8090168
Received: 3 August 2017 / Revised: 24 August 2017 / Accepted: 6 September 2017 / Published: 8 September 2017
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Abstract
Ventilation in cities is crucial for the well being of their inhabitants. Therefore, local governments require air ventilation assessments (AVAs) prior to the construction of new buildings. In a standard AVA, however, only neutral stratification is considered, although diabatic and particularly unstable conditions
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Ventilation in cities is crucial for the well being of their inhabitants. Therefore, local governments require air ventilation assessments (AVAs) prior to the construction of new buildings. In a standard AVA, however, only neutral stratification is considered, although diabatic and particularly unstable conditions may be observed more frequently in nature. The results presented here indicate significant changes in ventilation within most of the area of Kowloon City, Hong Kong, included in the study. A new definition for calculating ventilation was introduced, and used to compare the influence of buildings on ventilation under conditions of neutral and unstable stratification. The overall ventilation increased due to enhanced vertical mixing. In the vicinity of exposed buildings, however, ventilation was weaker for unstable stratification than for neutral stratification. The influence on ventilation by building parameters, such as the plan area index, was altered when unstable stratification was considered. Consequently, differences in stratification were shown to have marked effects on ventilation estimates, which should be taken into consideration in future AVAs. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Impacts of Urban Layouts and Open Space on Urban Ventilation Evaluated by Concentration Decay Method
Atmosphere 2017, 8(9), 169; doi:10.3390/atmos8090169
Received: 20 August 2017 / Revised: 6 September 2017 / Accepted: 6 September 2017 / Published: 11 September 2017
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Abstract
Previous researchers calculated air change rate per hour (ACH) in the urban canopy layers (UCL) by integrating the normal component of air mean velocity (convection) and fluctuation velocity (turbulent diffusions) across UCL boundaries. However they are usually greater than the actual
[...] Read more.
Previous researchers calculated air change rate per hour (ACH) in the urban canopy layers (UCL) by integrating the normal component of air mean velocity (convection) and fluctuation velocity (turbulent diffusions) across UCL boundaries. However they are usually greater than the actual ACH induced by flow rates flushing UCL and never returning again. As a novelty, this paper aims to verify the exponential concentration decay history occurring in UCL models and applies the concentration decay method to assess the actual UCL ACH and predict the urban age of air at various points. Computational fluid dynamic (CFD) simulations with the standard k-ε models are successfully validated by wind tunnel data. The typical street-scale UCL models are studied under neutral atmospheric conditions. Larger urban size attains smaller ACH. For square overall urban form (Lx = Ly = 390 m), the parallel wind (θ = 0°) attains greater ACH than non-parallel wind (θ = 15°, 30°, 45°), but it experiences smaller ACH than the rectangular urban form (Lx = 570 m, Ly = 270 m) under most wind directions (θ = 30° to 90°). Open space increases ACH more effectively under oblique wind (θ = 15°, 30°, 45°) than parallel wind. Although further investigations are still required, this paper provides an effective approach to quantify the actual ACH in urban-like geometries. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Data Assimilation in Air Contaminant Dispersion Using a Particle Filter and Expectation-Maximization Algorithm
Atmosphere 2017, 8(9), 170; doi:10.3390/atmos8090170
Received: 27 July 2017 / Revised: 6 September 2017 / Accepted: 8 September 2017 / Published: 16 September 2017
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Abstract
The accurate prediction of air contaminant dispersion is essential to air quality monitoring and the emergency management of contaminant gas leakage incidents in chemical industry parks. Conventional atmospheric dispersion models can seldom give accurate predictions due to inaccurate input parameters. In order to
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The accurate prediction of air contaminant dispersion is essential to air quality monitoring and the emergency management of contaminant gas leakage incidents in chemical industry parks. Conventional atmospheric dispersion models can seldom give accurate predictions due to inaccurate input parameters. In order to improve the prediction accuracy of dispersion models, two data assimilation methods (i.e., the typical particle filter & the combination of a particle filter and expectation-maximization algorithm) are proposed to assimilate the virtual Unmanned Aerial Vehicle (UAV) observations with measurement error into the atmospheric dispersion model. Two emission cases with different dimensions of state parameters are considered. To test the performances of the proposed methods, two numerical experiments corresponding to the two emission cases are designed and implemented. The results show that the particle filter can effectively estimate the model parameters and improve the accuracy of model predictions when the dimension of state parameters is relatively low. In contrast, when the dimension of state parameters becomes higher, the method of particle filter combining the expectation-maximization algorithm performs better in terms of the parameter estimation accuracy. Therefore, the proposed data assimilation methods are able to effectively support air quality monitoring and emergency management in chemical industry parks. Full article
(This article belongs to the Special Issue Efficient Formulation and Implementation of Data Assimilation Methods)
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Open AccessArticle Remote Ocean Response to the Madden–Julian Oscillation during the DYNAMO Field Campaign: Impact on Somali Current System and the Seychelles–Chagos Thermocline Ridge
Atmosphere 2017, 8(9), 171; doi:10.3390/atmos8090171
Received: 15 August 2017 / Revised: 9 September 2017 / Accepted: 10 September 2017 / Published: 13 September 2017
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Abstract
During the CINDY/DYNAMO field campaign, exceptionally large upper ocean responses to strong westerly wind events associated with the Madden–Julian oscillation (MJO) were observed in the central equatorial Indian Ocean. Strong eastward equatorial currents in the upper ocean lasted more than one month from
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During the CINDY/DYNAMO field campaign, exceptionally large upper ocean responses to strong westerly wind events associated with the Madden–Julian oscillation (MJO) were observed in the central equatorial Indian Ocean. Strong eastward equatorial currents in the upper ocean lasted more than one month from late November 2011 to early January 2012. The remote ocean response to these unique MJO events are investigated using a high resolution (1/25°) global ocean general circulation model along with the satellite altimeter data. The local ocean response to the MJO events are realistically simulated by the global model based on the comparison with the data collected during the field campaign. The satellite altimeter data show that anomalous sea surface height (SSH) associated with the strong eastward jets propagated eastward as an equatorial Kelvin wave. The positive SSH anomalies then partly propagate westward as a reflected Rossby wave. The SSH anomalies associated with the reflected Rossby wave in the southern hemisphere propagate all the way to the western boundary. These remote ocean responses are well simulated by the global model. The analysis of the model simulation indicates the significant influence of reflected Rossby waves on sub-seasonal variability of Somali current system near the equator. The analysis further suggests that the reflected Rossby wave causes a substantial change in the structure of the Seychelles–Chagos thermocline ridge, which contributes to significant SST anomalies. Full article
(This article belongs to the Special Issue Madden-Julian Oscillation)
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Open AccessArticle Validation of MODIS-Aqua Aerosol Products C051 and C006 over the Beijing-Tianjin-Hebei Region
Atmosphere 2017, 8(9), 172; doi:10.3390/atmos8090172
Received: 31 July 2017 / Revised: 24 August 2017 / Accepted: 12 September 2017 / Published: 14 September 2017
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Abstract
The recently released MODerate resolution Imaging Spectroradiometers (MODIS) Collection 6(C006) includes several significant improvements, which are expected to do well in analyzing aerosols and using the observations for air pollution application. The C006 Aerosol Optical Depth (AOD) retrievals should be validated completely before
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The recently released MODerate resolution Imaging Spectroradiometers (MODIS) Collection 6(C006) includes several significant improvements, which are expected to do well in analyzing aerosols and using the observations for air pollution application. The C006 Aerosol Optical Depth (AOD) retrievals should be validated completely before they will be applied to specific research. However, the validation of C006 AOD retrievals at a regional scale is limited. Therefore, this study evaluated the performance of the MODIS-Aqua Collection 51 (C051) and C006 AOD retrievals over the Beijing-Tianjin-Hebei region in China from 2006 to 2015 using ground-based Sun photometers. The algorithms of the AOD product include Dark Target (DT) and Deep Blue (DB). The results indicated that the improvements in DT C006 were slight, as the expected error (EE) increased by almost 9% over the two sites, and the DT C051 and DT C006 AOD were overestimated for both sites. DB C006 presented an improvement over DB C051, and a better correlation was observed between the collocated DB C006 retrievals and Sun photometer data (R ranged from 0.9343–0.9383). There was an increase in the frequency from DT C051 to DT C006, in the range 0.6–1.5, over the two sites; moreover, the AOD from the DB retrievals had a very narrow range (0.1–0.3). The spatial distribution of the AOD values was high (AOD > 0.7) over the southeastern region and low (AOD < 0.3) over the northwestern region. Changes in the DT C006 algorithm resulted in an increased AOD (0.085) for the region. The AOD values in spring and summer were higher than those in fall and winter. By subtracting the C051 AOD from the corresponding C006 values, greater positive changes (~0.2) were found in the southeastern areas during summer, presumably as the updated cloud-masking allowed heavy smoke retrievals. The accuracy of the AOD retrievals depended on the assumptions of surface reflectance and the selection of the aerosol model. The use of the DB C006 algorithm is recommended for the Beijing and Xianghe sites. Because of the limitations of the DT algorithm over sparsely vegetated surfaces, the DT C006 product is recommended for Xianghe. Full article
(This article belongs to the Special Issue Aerosol Optical Properties: Models, Methods & Measurements)
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Open AccessArticle Elemental Mixing State of Aerosol Particles Collected in Central Amazonia during GoAmazon2014/15
Atmosphere 2017, 8(9), 173; doi:10.3390/atmos8090173
Received: 31 July 2017 / Revised: 6 September 2017 / Accepted: 12 September 2017 / Published: 15 September 2017
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Abstract
Two complementary techniques, Scanning Transmission X-ray Microscopy/Near Edge Fine Structure spectroscopy (STXM/NEXAFS) and Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDX), have been quantitatively combined to characterize individual atmospheric particles. This pair of techniques was applied to particle samples at three sampling sites (ATTO,
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Two complementary techniques, Scanning Transmission X-ray Microscopy/Near Edge Fine Structure spectroscopy (STXM/NEXAFS) and Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDX), have been quantitatively combined to characterize individual atmospheric particles. This pair of techniques was applied to particle samples at three sampling sites (ATTO, ZF2, and T3) in the Amazon basin as part of the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) field campaign during the dry season of 2014. The combined data was subjected to k-means clustering using mass fractions of the following elements: C, N, O, Na, Mg, P, S, Cl, K, Ca, Mn, Fe, Ni, and Zn. Cluster analysis identified 12 particle types across different sampling sites and particle sizes. Samples from the remote Amazon Tall Tower Observatory (ATTO, also T0a) exhibited less cluster variety and fewer anthropogenic clusters than samples collected at the sites nearer to the Manaus metropolitan region, ZF2 (also T0t) or T3. Samples from the ZF2 site contained aged/anthropogenic clusters not readily explained by transport from ATTO or Manaus, possibly suggesting the effects of long range atmospheric transport or other local aerosol sources present during sampling. In addition, this data set allowed for recently established diversity parameters to be calculated. All sample periods had high mixing state indices (χ) that were >0.8. Two individual particle diversity (Di) populations were observed, with particles <0.5 µm having a Di of ~2.4 and >0.5 µm particles having a Di of ~3.6, which likely correspond to fresh and aged aerosols, respectively. The diversity parameters determined by the quantitative method presented here will serve to aid in the accurate representation of aerosol mixing state, source apportionment, and aging in both less polluted and more developed environments in the Amazon Basin. Full article
(This article belongs to the Special Issue Morphology and Internal Mixing of Atmospheric Particles)
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Open AccessArticle An Alternative Multi-Model Ensemble Forecast for Tropical Cyclone Tracks in the Western North Pacific
Atmosphere 2017, 8(9), 174; doi:10.3390/atmos8090174
Received: 7 June 2017 / Revised: 9 September 2017 / Accepted: 12 September 2017 / Published: 15 September 2017
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Abstract
This study introduces an unequally weighted technique for Multi-model Ensemble (MME) forecasting for western North Pacific Tropical Cyclone (TC) tracks. Weights are calculated by partial least square regression, and members are selected by paired t-test. The performances for shorter forecast time ranges,
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This study introduces an unequally weighted technique for Multi-model Ensemble (MME) forecasting for western North Pacific Tropical Cyclone (TC) tracks. Weights are calculated by partial least square regression, and members are selected by paired t-test. The performances for shorter forecast time ranges, such as 24, 48 and 72 h, are examined in order to improve the MME model, in which the weights for members are equally assigned. For longer forecast time ranges, such as 96 and 120 h, weights for MME members are thought to be less reliable, since the modeling is more likely to be influenced by the climate variability in the data period. A combination of both techniques for the shorter and the longer forecast time ranges is suggested as an alternative MME forecast procedure in operational meteorological agencies. Full article
(This article belongs to the Special Issue Tropical Cyclones and Their Impacts)
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Open AccessArticle Stomatal and Non-Stomatal Turbulent Deposition Flux of Ozone to a Managed Peatland
Atmosphere 2017, 8(9), 175; doi:10.3390/atmos8090175
Received: 24 June 2017 / Revised: 11 September 2017 / Accepted: 12 September 2017 / Published: 16 September 2017
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Abstract
Ozone is a key trace gas in the troposphere; because it is a greenhouse gas, it is very reactive, and it is potentially toxic to humans, fauna, and vegetation. The main sink processes for ozone are chemical reactions and the turbulent deposition flux
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Ozone is a key trace gas in the troposphere; because it is a greenhouse gas, it is very reactive, and it is potentially toxic to humans, fauna, and vegetation. The main sink processes for ozone are chemical reactions and the turbulent deposition flux to the earth’s surface. The deposition process itself is rather complex: The interactions between co-varying drivers such as the tropospheric ozone concentration, turbulence, and chemical reactions are not well understood. In the case of ozone deposition to vegetation, another aspect that must be studied is the role of stomatal regulation for a wide range of conditions. Therefore, we measured turbulent deposition fluxes of ozone with the eddy covariance technique during the peak of the growing season in 2014 over a managed, rewetted peatland in NW Germany. The deposition flux was large during the day (up to −15 nmol m−2 s−1) and relatively small during the night (between −1 and −2 nmol m−2 s−1). Flux partitioning by applying the surface resistance analogy and further analysis showed that the stomatal uptake was smaller than non-stomatal deposition. The correction of stomatal conductance with the gross primary production (GPP) improved the estimation of day- and nighttime stomatal deposition fluxes. Statistical analysis confirmed that the friction velocity (u*) was the single most important driver of non-stomatal ozone deposition and that relationships with other environmental drivers are not linear and highly variable. Further research is needed to develop a better process understanding of non-stomatal ozone deposition, to quantify the role of surface deposition to the ozone budget of the atmospheric boundary layer, and to estimate uncertainties associated with the partitioning of ozone deposition into stomatal and non-stomatal fluxes. Full article
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Open AccessArticle Vertical Sampling Scales for Atmospheric Boundary Layer Measurements from Small Unmanned Aircraft Systems (sUAS)
Atmosphere 2017, 8(9), 176; doi:10.3390/atmos8090176
Received: 25 July 2017 / Revised: 29 August 2017 / Accepted: 13 September 2017 / Published: 17 September 2017
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Abstract
The lowest portion of the Earth’s atmosphere, known as the atmospheric boundary layer (ABL), plays an important role in the formation of weather events. Simple meteorological measurements collected from within the ABL, such as temperature, pressure, humidity, and wind velocity, are key to
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The lowest portion of the Earth’s atmosphere, known as the atmospheric boundary layer (ABL), plays an important role in the formation of weather events. Simple meteorological measurements collected from within the ABL, such as temperature, pressure, humidity, and wind velocity, are key to understanding the exchange of energy within this region, but conventional surveillance techniques such as towers, radar, weather balloons, and satellites do not provide adequate spatial and/or temporal coverage for monitoring weather events. Small unmanned aircraft, or aerial, systems (sUAS) provide a versatile, dynamic platform for atmospheric sensing that can provide higher spatio-temporal sampling frequencies than available through most satellite sensing methods. They are also able to sense portions of the atmosphere that cannot be measured from ground-based radar, weather stations, or weather balloons and have the potential to fill gaps in atmospheric sampling. However, research on the vertical sampling scales for collecting atmospheric measurements from sUAS and the variabilities of these scales across atmospheric phenomena (e.g., temperature and humidity) is needed. The objective of this study is to use variogram analysis, a common geostatistical technique, to determine optimal spatial sampling scales for two atmospheric variables (temperature and relative humidity) captured from sUAS. Results show that vertical sampling scales of approximately 3 m for temperature and 1.5–2 m for relative humidity were sufficient to capture the spatial structure of these phenomena under the conditions tested. Future work is needed to model these scales across the entire ABL as well as under variable conditions. Full article
(This article belongs to the Special Issue Atmospheric Measurements with Unmanned Aerial Systems (UAS))
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Open AccessArticle Assessment of Natural Ventilation Potential for Residential Buildings across Different Climate Zones in Australia
Atmosphere 2017, 8(9), 177; doi:10.3390/atmos8090177
Received: 3 September 2017 / Revised: 14 September 2017 / Accepted: 16 September 2017 / Published: 20 September 2017
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Abstract
In this study, the natural ventilation potential of residential buildings was numerically investigated based on a typical single-story house in the three most populous climate zones in Australia. Simulations using the commercial simulation software TRNSYS (Transient System Simulation Tool) were performed for all
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In this study, the natural ventilation potential of residential buildings was numerically investigated based on a typical single-story house in the three most populous climate zones in Australia. Simulations using the commercial simulation software TRNSYS (Transient System Simulation Tool) were performed for all seasons in three representative cities, i.e., Darwin for the hot humid summer and warm winter zone, Sydney for the mild temperate zone, and Melbourne for the cool temperate zone. A natural ventilation control strategy was generated by the rule-based decision-tree method based on the local climates. Natural ventilation hour (NVH) and satisfied natural ventilation hour (SNVH) were employed to evaluate the potential of natural ventilation in each city considering local climate and local indoor thermal comfort requirements, respectively. The numerical results revealed that natural ventilation potential was related to the local climate. The greatest natural ventilation potential for the case study building was observed in Darwin with an annual 4141 SNVH out of 4728 NVH, while the least natural ventilation potential was found in the Melbourne case. Moreover, summer and transition seasons (spring and autumn) were found to be the optimal periods to sustain indoor thermal comfort by utilising natural ventilation in Sydney and Melbourne. By contrast, natural ventilation was found applicable over the whole year in Darwin. In addition, the indoor operative temperature results demonstrated that indoor thermal comfort can be maintained only by utilising natural ventilation for all cases during the whole year, except for the non-natural ventilation periods in summer in Darwin and winter in Melbourne. These findings could improve the understanding of natural ventilation potential in different climates, and are beneficial for the climate-conscious design of residential buildings in Australia. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Variability of Precipitation in Arid Climates Using the Wavelet Approach: Case Study of Watershed of Gabes in South-East Tunisia
Atmosphere 2017, 8(9), 178; doi:10.3390/atmos8090178
Received: 20 July 2017 / Revised: 7 September 2017 / Accepted: 15 September 2017 / Published: 20 September 2017
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Abstract
This study examines the variability of precipitation in the south-east of Tunisia through the analysis of data about annual and monthly precipitation at five stations in the Watershed of Gabes, from 1977 to 2015. Standardized precipitation ratio, wavelet and coherence wavelet analyses were
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This study examines the variability of precipitation in the south-east of Tunisia through the analysis of data about annual and monthly precipitation at five stations in the Watershed of Gabes, from 1977 to 2015. Standardized precipitation ratio, wavelet and coherence wavelet analyses were applied to examine the temporal variability of monthly and annual precipitation and to determine the effect of climatic fluctuations on rainfall variability. Results of wavelet analysis showed varied energy bands at the studied stations at annual and inter-annual scales. The depicted bands spread according to intervals of 1-, 2- to 4-, 4- to 8- and 8- to 12-year cycles, obviously influenced by regional factors including altitude, proximity to the Mediterranean Sea and global fluctuations. Eventually, an analysis of wavelet coherence showed a strong correlation between precipitation and Mediterranean Oscillation (MO) in Gabes Watershed at different temporal scales. Contribution of the MO ranged between 51% and 93% of fluctuations (8–12 years) in the different examined rainfall stations. Full article
(This article belongs to the Special Issue Precipitation Variability and Change in Africa)
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Open AccessArticle Multi-Year (2013–2016) PM2.5 Wildfire Pollution Exposure over North America as Determined from Operational Air Quality Forecasts
Atmosphere 2017, 8(9), 179; doi:10.3390/atmos8090179
Received: 30 June 2017 / Revised: 8 September 2017 / Accepted: 14 September 2017 / Published: 19 September 2017
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Abstract
FireWork is an on-line, one-way coupled meteorology–chemistry model based on near-real-time wildfire emissions. It was developed by Environment and Climate Change Canada to deliver operational real-time forecasts of biomass-burning pollutants, in particular fine particulate matter (PM2.5), over North America. Such forecasts
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FireWork is an on-line, one-way coupled meteorology–chemistry model based on near-real-time wildfire emissions. It was developed by Environment and Climate Change Canada to deliver operational real-time forecasts of biomass-burning pollutants, in particular fine particulate matter (PM2.5), over North America. Such forecasts provide guidance for early air quality alerts that could reduce air pollution exposure and protect human health. A multi-year (2013–2016) analysis of FireWork forecasts over a five-month period (May to September) was conducted. This work used an archive of FireWork outputs to quantify wildfire contributions to total PM2.5 surface concentrations across North America. Different concentration thresholds (0.2 to 28 µg/m3) and averaging periods (24 h to five months) were considered. Analysis suggested that, on average over the fire season, 76% of Canadians and 69% of Americans were affected by seasonal wildfire-related PM2.5 concentrations above 0.2 µg/m3. These effects were particularly pronounced in July and August. Futhermore, the analysis showed that fire emissions contributed more than 1 µg/m3 of daily average PM2.5 concentrations on more than 30% of days in the western USA and northwestern Canada during the fire season. Full article
(This article belongs to the Special Issue Air Quality Monitoring and Forecasting)
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Open AccessArticle The Madden-Julian Oscillation: A Tool for Regional Seasonal Precipitation Outlooks?
Atmosphere 2017, 8(9), 180; doi:10.3390/atmos8090180
Received: 15 August 2017 / Revised: 7 September 2017 / Accepted: 15 September 2017 / Published: 20 September 2017
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Abstract
The Madden-Julian Oscillation (MJO) is an important intraseasonal climate signal which circles the global tropics, but also impacts extratropical weather regimes. Few studies have investigated whether the MJO is a source of regional seasonal climate predictability. The present objective is to determine the
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The Madden-Julian Oscillation (MJO) is an important intraseasonal climate signal which circles the global tropics, but also impacts extratropical weather regimes. Few studies have investigated whether the MJO is a source of regional seasonal climate predictability. The present objective is to determine the extent to which the season and phase (geographic location) of MJO contribute to the frequency of global rainfall anomalies in ensuing seasons. Indices of June-July-August and December-January-February MJO activity for each phase and the El Niño/Southern Oscillation (ENSO) were correlated to three-month averages of rainfall up to a six-month lead time. Field significance was calculated and patterns of the relationships were described. In general, MJO shows some skill in regional seasonal precipitation prediction, but to a lesser extent than ENSO. However, the presence of MJO in the western Indian Ocean and near the date line did reveal a persistent and significant relationship with regional seasonal rainfall, especially over Northern Hemisphere land areas. Full article
(This article belongs to the Special Issue Madden-Julian Oscillation)
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Review

Jump to: Research

Open AccessReview Tropospheric Ozone at Northern Mid-Latitudes: Modeled and Measured Long-Term Changes
Atmosphere 2017, 8(9), 163; doi:10.3390/atmos8090163
Received: 8 June 2017 / Revised: 11 August 2017 / Accepted: 13 August 2017 / Published: 29 August 2017
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Abstract
In this paper, we investigate why current state-of-the-art chemistry-climate models underestimate the tropospheric ozone increase from the 1950s to the 1990s by approximately 50%. The accuracy of these models is vital, not only for understanding and predicting air quality globally, but also since
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In this paper, we investigate why current state-of-the-art chemistry-climate models underestimate the tropospheric ozone increase from the 1950s to the 1990s by approximately 50%. The accuracy of these models is vital, not only for understanding and predicting air quality globally, but also since they are used to quantify the contribution of ozone in the troposphere and lower stratosphere to climate change, where its greenhouse effect is largest. We briefly describe available northern mid-latitude ozone measurements, which include representative and reliable data from European sites that extend back to the 1950s. We use the SOCOLv3 (Solar Climate Ozone Links version 3) global chemistry-climate model to investigate the individual terms of the tropospheric ozone budget. These include: inflow from the stratosphere, dry deposition, and chemical formation and destruction. For 1960 to 2000 SOCOLv3 indicates a tropospheric ozone increase at 850 hPa over the Swiss Alps (Arosa) of 17 ppb, or around 30%. This increase is smaller than that seen in the surface ozone measurements but similar to other chemistry-climate models, including those with more complex NMVOC (Non Methane Volatile Organic Compound) schemes than SOCOLv3’s. It is likely that the underestimated increase in tropospheric ozone could be explained by issues in the underlying emissions inventories used in the model simulations, with ozone precursor emissions, particularly NOx (NO + NO2), from the 1960s being too large. Full article
(This article belongs to the Special Issue Tropospheric Ozone and Its Precursors)
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