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  • Open access
  • 66 Reads
Simulations of Pollutant Diffusion under Different Meteorological Conditions

Pollutants enter into the atmospheric boundary layer (ABL) after emitted from surface sources, which has a great influence on the health of human beings. The diffusion of the pollutants within the ABL is strongly affected by meteorological conditions, such as the radiation, wind speed and turbulent mixing. In order to estimate the effects caused by different meteorological factors on the diffusion, in this study, finite difference method was used to solve the diffusion equation of pollutant. The solution was first compared with the theoretical solution, in order to verify the correctness of the model. Moreover, the model was extended to three dimensions, by considering the vertical mixing between different vertical layers. In this study, we obtained the spatial and temporal evolution of pollutants under different wind speed conditions for different types of pollutant source distribution, which is of guiding significance for the planning and locating of industrial zones in cities.

  • Open access
  • 58 Reads
Do Sunspots Determine the Integrity of Satellite Navigation Signal? Fuzzy Logic Approach

Analysis of the phenomena related to the satellite signal used operationally in civil aviation is not possible without a model analysis. Experimenting on an actual flight operation can lead to dramatic effects. Therefore, numerous attempts are made to study the signal and the processes taking place in satellite systems during operation, which have a potential impact on its disturbance. At the same time, the interest in the implementation of satellite techniques to various areas of air traffic is clearly visible. There is also a noticeable number of studies carried out on both the operational parameters of satellite systems and the satellite signal itself. The aim of such tests is to achieve the best possible results, inter alia, in terms of signal integrity. It also seems of key importance that the atmophere condition in any area of ​​aviation should not be underestimated due to its extensive impact. It has been proven, in the world literature, that the ionospheric factor is seriously limiting the operational use of the satellite navigation signal. For aviation, it remains a particularly important aspect to provide information about the integrity of the data transmitted to the user. The aim of the article is therefore to check whether the ionospheric factor, determined by solar activity, significantly affects the integrity of the satellite signal. For this purpose, a fuzzy logic approach will be used. Literature sources define two approaches to fuzzy control - descriptive and prescriptive. The first is based on the expert knowledge of the operator who knows from experience how to control the process. This is a traditional approach, not based on an existing model. The second approach assumes the existence of a stochastic or deterministic model and determines how to optimally control it. In the article, the traditional approach is closer to research. The model of the process determining the output (satellite signal integrity) as a function of the input (solar activity) is unknown. This means that this process is a black box. However, knowledge is available on how to control the process well, i.e. what control to choose for the current output.

  • Open access
  • 72 Reads
Probabilistic Forecast of Visibility of Gimpo, Incheon and Jeju International Airports Using Weighted Model Averaging

In this study, the weighted model averaging (WMA) was applied to calibrate ensemble forecasts generated from Local ENsemble prediction System (LENS). The WMA technique, which is easy to implement post-processing technique and lays greater weight on ensemble member forecast that exhibits the best performance, provides probabilistic visibility forecasting that takes the form of predictive probability density function for ensembles. The predictive probability density function used is a mixture of discrete point mass and two-sided truncated normal distribution components. Observations were obtained from the 3 International Airports (Gimpo, Incheon and Jeju) and 13 ensemble member forecasts derived from the LENS that were obtained between December 2018 and June 2019. Prior to applying to WMA, reliability analysis was conducted by using rank histogram and reliability diagram to identify the statistical consistency of ensembles and corresponding observations. Then, WMA method was applied to each raw ensemble model and proposed a weighted predictive probability density function. The performances were evaluated by mean absolute error, continuous ranked probability score, Brier score and probability integral transform. The results showed that the proposed method provide improved performances than the raw ensemble, indicating the predictive probability density function is well calibrated with respected to raw ensemble.

  • Open access
  • 174 Reads
Moisture Transport toward Europe and Extreme Precipitation Events

In the last decades an increase in extreme precipitation events was observed all over the world and, specifically, over Europe. The moisture transport from oceans toward the continent is one of the main factors affecting precipitation patterns. Due to the influence of climate change on moisture transport, investigating the changes in moisture transport from the oceanic sources is of especial interest; resulting especially relevant the association between transport changes and extreme precipitation events. For the European region, two main moisture sources were found to contribute to precipitation, namely the North Atlantic Ocean and the Mediterranean Sea. In this work, the lagrangian particle dispersion model FLEXPART is applied in order to investigate the contribution from these two sources over the region. The moisture contribution is computed taking into account both, climatological mean and extreme precipitation events. From the result, a redistribution on the contribution from the source is observed associated with precipitation events.

  • Open access
  • 141 Reads
A 15-Year Climatology of Desert Dust Episodes in the Broader Mediterranean Basin
Published: 13 November 2020 by MDPI in The 3rd International Electronic Conference on Atmospheric Sciences session Aerosols

Dust is the Earth’s most abundant aerosol type, mostly originating from great deserts (Sahara, Taklimakan, Gobi, Middle East), but also from agricultural and construction activities. The emitted dust remains in the atmosphere from a few hours up to several days, while under favorable conditions is transported far from its sources. During this transport, the physical and chemical properties of dust can change, thus affecting its action as Cloud Condensation Nuclei (CNN) or Ice Nuclei (IN) as well as its interaction with radiation, consequently modifying the radiation and energy budget of the areas affected by the dust transport. There is need for improving scientific knowledge about dust transport, especially over areas like the Mediterranean basin (MB), which is close to the Sahara, Middle East, and Arabian deserts, and frequently undergoes dust transport, resulting in dust aerosol episodes (DAE). In the present study, DAEs in the broader MB are investigated over a 15-year (2005-2019) period using contemporary MODIS Collection 6.1 and OMI OMAERUV satellite data and a satellite algorithm applying a thresholding technique on selected aerosol optical properties. The algorithm operates on a daily and 1°x1° pixel level basis, first identifying the presence of dust, and consequently requiring the presence of unusual high dust loads, i.e. dust episodes. Apart from the presence of pixel level DAEs, an extended spatial coverage is also required. Thus, a specific day is characterized as a Dust Aerosol Episode Day (DAED), when at least 30 episodic pixels exist. According to the algorithm results, 166 DAEDs (116 strong and 50 extreme) took place in the MB from 2005 to 2019. The greatest part of DAEDs occurred in spring (47%) and summer (38%), while a different seasonality is observed for strong and extreme episodes. The interannual variability of DAEDs reveal a decreasing trend, which is not statistically significant.

  • Open access
  • 105 Reads
Trends and Spatial Characteristics of PM1 Aerosol Chemical Composition over the Greater Athens Area, Using High Temporal Resolution Measurements

Airborne sub-micrometer particles (PM1) have been documented to exert adverse impacts to human health, including respiratory and cardiovascular disease and premature mortality. The Greater Athens Area (GAA), characterized by topographic and meteorological conditions which frequently obstruct the effective dispersion of ambient pollutants, hosts approximately 40% of Greece’s population. It can be considered as a suitable ambient laboratory for studying PM1 pollution events, given the intensity and diversity of PM1 sources and processing.

PM1 chemical composition was continuously monitored at the National Observatory of Athens Air Monitoring Station at Thissio, an urban background site in central Athens. Furthermore, two intensive monthly campaigns were held in Piraeus, where Greece’s busiest passenger port is located, during both winter (Dec 2018-Jan 2019) and summer (Jun-Jul 2019). Instrumentation in Piraeus was placed at the central metro station building.

Organic aerosol (OA), sulfate, nitrate, ammonium and chloride were measured using an Aerosol Chemical Speciation Monitor (ACSM) while black carbon (BC) was measured using an aethalometer (AE-33). Positive matrix factorization (PMF) source apportionment was performed on OA mass spectra, identifying primary (hydrocarbon-like, biomass-burning and cooking aerosol) and secondary (low- and semi-volatile oxygenated OA) sources, while spectral properties of absorption, were used to discern between BC from fossil fuel combustion (BCff) or biomass burning (BCbb).

Variability of concentrations at different temporal scales and general characteristics of spatial variability were investigated along with potential intra-urban and long-range transport mechanisms. Biomass burning related to domestic heating was found to be a key factor during wintertime, while PM1 aerosol concentrations were found to be similar at both locations. On the contrary, during summertime, Piraeus was found to be more burdened than Thissio, with local sources related to increased passenger and ship traffic playing an important role. Nevertheless, secondary sources were found to affect both sites in a homogeneous manner.

  • Open access
  • 60 Reads
Numerical Simulation of Nocturnal Ozone Increase in Metropolitan Area of São Paulo

In large cities, pollution can not only cause deaths and illnesses due to exposure of people to it, but it can also reduce visibility on days of high atmospheric stability and high emission of pollutants, which can even result in vehicular accidents. Ozone is an atmospheric oxidizing gas that forms in minimal amounts naturally. People's health can be affected by the ozone present in the air they breathe, even in low concentrations, which can worsen preexisting diseases and increase hospital admissions for respiratory diseases, especially in babies, after episodes of high levels of this pollutant. An increase in secondary peaks during the night of this atmospheric pollutant occurs in several parts of the world, but its formation depends on the local condition. In this sense, this work aims to study the regional atmospheric characteristics for the nocturnal ozone formation in the Metropolitan Area of São Paulo (MASP). For this, the Simple Photochemical Module (SPM) coupled to the BRAMS (Brazilian Developments of Regional Atmospheric Modeling System) will be used to simulate this condition for the urban region. The results showed that the secondary nocturnal maximum of ozone concentrations in MASP is related to vertical transport of this pollutant from higher levels of the atmosphere to the surface.

  • Open access
  • 89 Reads
Estimation of Crop Production, CO2 Fluxes and Carbon Budget Using Remote Sensing: Application to Winter Wheat/Sunflower Rotations

A recent study has proposed and validated an approach based on the use of an agro-meteorological model assimilating remote sensing products, to simulate development, production, CO2 fluxes and thus carbon budget for winter wheat in southwest France. This model (SAFY-CO2) was validated thanks to data acquired at two instrumented ICOS sites and close to 16 fields in our area of study. It was able to accurately reproduce biomass and yield (rRMSE of 27% and 21%, respectively) as well as the daily net CO2 flux (RMSE of 1.29 gC.m-2.d-1) allowing to estimate accurate net annual ecosystem carbon budget (NECB). The use of remote sensing products (green area index) drastically limits the need for ground measurement or information about agricultural practices. This specificity allows the model to be upscale easily and to simulate crop rotations without any in situ information other than that provided by satellites.

Based on these results, we propose a further analysis allowing to estimate the carbon budget of cropland over several years. In this study, the model has been adapted to run in multi-year and applied at the regional scale in southwest France. Besides winter wheat, sunflower has also been implemented in the model in order to simulate winter wheat/sunflower rotations, which are the two main cultivated crops in the study area.

The model showed good performances at estimating sunflower biomass and yield (RMSE of 66 and 55 g.m-2, respectively) as well as the net CO2 flux (RMSE of 0.97gC.m-2.d-1), which allows to simulate crop rotations.

In addition to remote sensing products from Sentinel 2 and Venμs satellites, we used the French Land Parcel Identification System which is the delimitation of French agricultural lands as well as the SAFRAN re-analysis meteorological data. This work allows to quantify the biogeochemical impact of certain crop rotation as well as agricultural practices. Indeed, the proposed approach accounts for potential vegetation development during fallow periods (weeds, cover crops) and scenarii with and without export of wheat straws as well as their impact on the NECB will be discussed.

  • Open access
  • 193 Reads
Analysis of Dry and Wet Episodes in Eastern South America during 1980-2018 Using SPEI

A large part of the population and the economic activities of South America are located in eastern continent (ESA). ESA is affected by the South American monsoon system, and most of the region belongs to the Amazon, Araguaia-Tocantins, and La Plata basins. The precipitation over ESA may be modulated by the moisture transported from the Atlantic Ocean, mainly the subtropical South Atlantic along the year, and particularly the tropical North portion during the Austral Summer. Extreme climate dry and wet episodes are a recurrent phenomenon in areas of ESA, with environmental and socio-economic impacts, and a quantitative assessment of occurrence of extreme climate events is essential for understanding, monitoring and mitigation of such episodes. This study aims to analyze the extreme climate events at domain-scale occurring over ESA over the last four decades through the multi-scalar Standardized Precipitation-Evapotranspiration Index (SPEI). Based on the results of a Lagrangian approach developed for moisture analysis, the study area consists in the major continental sink of the moisture transported from the Subtropical South Atlantic Ocean towards South America, comprising the Amazonia, almost all the Brazilian territory, and La Plata regions. The SPEI was calculated for the period 1980-2018 using monthly CRU (TS4.03) precipitation and potential evapotranspiration time series (at an original spatial resolution of 0.5 degrees) averaged over the study area. The extreme episodes affecting different components of the hydrological cycle were identified through the SPEI-1, SPEI-3, SPEI-6, and SPEI-12 time series, and their respective indicators (duration, severity, intensity, and peak) were then computed. Preliminary results indicate the predominance of dry episodes in the 2010 decade, while the wet ones prevailed in the middle of the 1990s. The role of the moisture transport from the South Atlantic on the occurrence of these extreme episodes will be investigated in a further study.

  • Open access
  • 76 Reads
Characterization of Persistent Air Quality Degradation Episodes of the PM10 in the Metropolitan Area of São Paulo and Their Relationship with Meteorological Conditions

Air pollution is one of the main environmental problems in large urban centers, harming people's health and impacting quality of life. The Metropolitan Area of São Paulo (MASP) presents frequent exceedances of air quality standards of the inhalable particulate matter pollutant (PM10), modulated by meteorological conditions, and its main pollutant sources are vehicular and industrial. This study aims to identify and characterize persistent overtaking episodes due to PM10 in the MASP between 2005 and 2017, relating them to meteorological conditions. The criteria used to select the events were: i) events that occurred in at least 50% of the air quality monitoring stations chosen for this study and, ii) among the events that met the first criterion, those with a duration equal to or greater than the 80% percentile. From the 71 persistent episodes of overtaking selected, the results show that the exceedances of inhalable particulate matter lasted up to 14 consecutive days and were predominant in the austral winter. The peak concentration stage of PM10 episodes were accompanied by an increase in maximum temperature (T), in addition to a decrease in wind speed (WS) and relative humidity (RH), besides the wind direction predominantly from the northwest. These patterns may be related to synoptic prefrontal conditions in the MASP.

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