Influence of Atmospheric Dynamic Factors on Dust Aerosol Mobilization Over West Africa: Simulations from WRF-Chem Abstract Air pollution modeling has proved to be an effective tool in the description of atmospheric processes including pollutants source identification, transport, and dissipation on a regional scale where data are relatively sparse. This work employs the Weather Research Forecast with Chemistry option (WRF-Chem) coupled model to describe the dynamic atmospheric factors responsible for the dust diversion through very unusual path in the West African region on the 20th March, 2010. The simulation process was carried out between 15th and 25th March, 2010 to capture the dust activities during this unusual dust occurrence. Modeled aerosol optical depth (AOD) calculated by integration of aerosol extinction coefficient (Qext) on the vertical column was compared with observations from AERONET ground sun photometers at wavelength 440 nm. The results showed very strong correlation between the observed and the modeled AOD. Root-mean-square error (RMSE) of 0.46, 0.35, 0.37, and 3.09 over Banizoumbou, Dakar and IER_Cinzana, and Ilorin stations respectively, was obtained. Higher RMSE over Ilorin showed a restraint in capturing the AOD over Ilorin. A significant weakening of the Tropical Easterly Jet (TEJ) on the 19th March coupled with an abrupt wind regime change from easterly to westerly on the 20th day of the month at the African Easterly Jet (AEJ) level was seen to play an important role in the diversion of dust into the region. In addition, the development of stronger vertical wind shear within the troposphere atmospheric layer played a crucial role in the development and unusual transport of dust into the West African region during this period. This study provides concrete evidences of atmospheric processes influencing the transport of the Saharan dust, from the source region to other parts of West Africa.

A study of PM 2.5–10 pollution at three functional receptor sites in a sub-Saharan African megacity Abstract PM2.5–10 (aerodynamic diameter dae 2.5 µm ≥ x ≤ 10 µm) pollution is rapidly becoming a serious problem in many urban areas especially in the least and middle income countries where air quality guidelines as well as urban infrastructure are grossly lacking. In this regards, PM2.5–10 samples collected within a 12-month period from the industrial, low- and high- density residential areas in Lagos Nigeria were studied. The PM2.5–10 were analyzed using ion beam analyses techniques vis-á-vis particle induced X-ray emission and particle induced γ-ray emission, Hybrid Single-particle Lagrangian Integrated Trajectory (HYSPLIT) and surface meteorological data as well as Positive matrix factorization model (PMF). The results showed that the average mass loads ranged from 150 to 606 µg m−3 (industrial) 110 to 460 µg m−3 (high density residential) and 76 to 298 µg m−3 (low density residential) and revealed gross violations of local and international guidelines. In addition, the wind roses indicated that the wind flow patterns could have significant impacts on PM2.5–10 mass loads. HYSPLIT model revealed that most high episodes were caused by pollutant accumulation (induced by low wind speed) and transport of pollutants from highly polluted regions. Data on the concentrations of 22 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Zr, and Pb) were obtained and used for receptor modeling by PMF technique. PMF results indicated that soil dust, physical construction and industrial activities were the major emissions of PM2.5–10 and could lead to negative health implications on the inhabitants of Lagos.

Characterizing Spatial Patterns of NO 2 and SO 2 in Xi’an by Passive Sampling Abstract Nitrogen dioxide (NO2) and sulfur dioxide (SO2) are important air pollutants that affect air quality, human health, and climate. The concentrations of NO2 and SO2 were measured in Xi’an, China with passive samplers deployed at 70 sites in summer and winter. The average concentrations of NO2 and SO2 were 19.82 μg m−3 and 2.24 μg m−3, respectively, in summer and 21.09 μg m−3 and 7.99 μg m−3 in winter. Statistical analyses showed that the seasonal differences in SO2 were significant but those for NO2 were not. The concentrations of NO2 and SO2 in the Beilin district were higher than other districts, while those in Baqiao were relatively low. The concentrations of NO2 in commercial mixed areas were higher compared with other functional areas, and SO2 in the residential/educational areas during winter was high. Spatial distributions of NO2 and SO2 were obtained by ordinary kriging interpolation, and the results showed high summertime NO2 concentrations in the central urban and northwestern parts of the sampling grid and high wintertime NO2 in the central part of the grid. Summer SO2 concentrations were higher in the northern and lower in the southern parts of the grid, while SO2 was in winter high in the mid-west and low in the east.

Effect of Particle Size on Collection Efficiency of ESP and RABH: A Case Study Abstract Electro Static Precipitator (ESP) is a conventional dust collecting equipment used in various process industries. Nowadays bag houses and Reverse Air Bag Houses (RABH) are also widely used in place of ESP. RABH is comparatively new technology which is used in cement plants and also other industrial facilities for dust collection. The dust collection efficiency of the ESP and RABH depend on many factors and particle size is one of those factors. Many researchers have done research on the collection efficiency of ESP with respect to the particle size distribution in dust-laden inlet gas, however, there is merely any study done on RABH collection efficiency with respect to the dust particle size distribution. A case study has been conducted in this research to find out the relationship between particle size distribution and collection efficiency of RABH in a cement plant. In addition to this, the collection efficiency of ESP is also studied with respect to the dust particle size distribution in inlet gas. The study has been conducted by taking the samples at inlet and outlet of ESP and RABH for calculation of efficiency and different particle size percentage at inlet side. It is found that the collection efficiency of both ESP and RABH is dependent on the size of the incoming dust load. In ESP the collection efficiency is higher when the particle size is smaller than 0.2 μm (PM0.2) and larger than 1 μm i.e., PM2.5 and PM10. The collection efficiency is lower when the particle size lies between 0.2 and 1 μm. In RABH it is observed that the collection efficiency increases with increase in the size of dust particles. Also a comparative study has been conducted to find out the better system between ESP and RABH by the help of sampling analysis (t test), field survey and performance parameter study. It is found that RABH is better than ESP in terms of collection efficiency and other performance parameters.

A Review of Synthesis, Structure and Applications in Hopcalite Catalysts for Carbon Monoxide Oxidation Abstract Carbon monoxide (CO) is a poisonous atmospheric pollutant. It highly affects human beings, plants, animals and environment. Automobile exhaust is the largest source of CO emission in the environment. To control this automobile exhaust pollution, the catalytic converters are used. Many types of catalysts have been investigated for CO oxidation purposes, i.e., noble metal, base metal, rare earth, perovskite, spinel and mixed transient metal oxides. These catalysts are widely used in a catalytic converter. Among the various metal oxide catalysts, hopcalite (CuMnOx) is one of the most efficient catalysts for low-temperature CO oxidation. Hopcalite catalysts have been reported to be good from economical, thermal, activity, selectivity and availability points of view. The activity of hopcalite catalysts is strongly dependent on the surface area, crystallite size and binding energy of the catalysts. This study will provide a scientific basis for designing future application of hopcalite catalysts for low-temperature CO oxidation. This manuscript provides a summary of published information regarding pure and substituted hopcalite catalyst, synthesis methods; properties and application for CO emissions control. A number of papers associated with CO oxidation over the hopcalite catalysts have been available, but no review papers appear in the literature that is dedicated to CO oxidation. Therefore, in an attempt to fill this gap, the present review updates and evaluates the progress and future scope of hopcalite catalyst for purification of exhaust gases.

Correction to: Atmospheric Aerosols: Some Highlights and Highlighters, 1950 to 2018 The article “Atmospheric Aerosols: Some Highlights and Highlighters.

Change of Ionization Mechanism in the Welding Fume Plasma from Gas Metal Arc Welding Abstract Ionization mechanisms in welding fumes from gas metal arc welding are studied. Welding fume is a low-temperature thermal plasma with ultra-violet radiation as external ionization source, where ionization occurs via gas particles’ collisions and photoionization. The plasma cooling causes heterogeneous ion-induced nucleation, which provides large number of nuclei. Nucleus number density is much greater than equilibrium number density of charge carriers. Electrons are captured by nuclei. As a result, the dust–ion plasma is formed, in which electron number density is much less than ion and nucleus number densities and it can be neglected. The surface atom ionization and ion recombination becomes predominant processes. Calculation of the plasma component number densities are presented as their evolution during welding fume cooling.

Atmospheric Particulate Matter Variations and Comparison of Two Forecasting Models for Two Indian Megacities Abstract Ambient particulate matter levels influence air quality and are an environmental risk factor, especially in megacities. Meteorological factors modulate the ambient concentration of particulates in the atmosphere and hence, human exposure, visibility degradation, and other environmental effects. It is, therefore, crucial to forecast particulate matter levels. Various methods have been used to forecast atmospheric particulate matter level. The present study uses fine particulate matter (PM2.5, particulate matter with aerodynamic diameter ≤ 2.5 micrometre) data from two megacities in South Asia to construct forecasting models—autoregressive (AR) and regression model and attempts to test the results. Delhi and Kolkata are the two cities for the study and data period is 2015–2017. Seasonal and diurnal trends are presented. Mean concentrations during the study period were highest in winter with daily concentrations exceeding the prescribed safe level by 3–7 times at both cities. Afternoon time was found to be the best time in a day with low particulate levels. Among meteorological parameters, temperature was found to have highest correlation (negative) with particulate matter at both the cities. Upon comparison with measured data for 15 days, it was found that AR model-estimated results do not exhibit the trend in the actual particulate levels, as is exhibited by the regression model estimations.

Intercomparison and Validation of Satellite and Ground-Based Aerosol Optical Depth (AOD) Retrievals over Six AERONET Sites in West Africa Abstract The geographical and climatic conditions of West Africa make the region an essential area for the description of atmospheric aerosol optical properties across the globe. This study provides an intercomparison of aerosol optical depth (AOD440nm) retrievals from satellite-based CALIPSO, MISR, MODIS and OMI sensors against ground-based sun photometer (AERONET) measurements between 2004 and 2014 from six West African sites, which are Agoufou, Banizoumbou, Ouagadougou, Dakar, Djougou and Ilorin during the period 2004–2014. The analysis revealed that MODISSTD performed better with a high degree of correlation for the six study sites, the CALIPSO and MISR–AERONET comparisons showed strong correlations, and the MODISDB also indicated better correlations, as did the OMI–AERONET comparisons. The root mean square error, mean absolute error and root mean bias error were also computed. The CALIPSO instrument has the lowest RMSE and MAE values over Dakar, while the highest RMSE and MAE values were indicated by the CALIPSO and MODISDB sensors, respectively, over Ilorin. The MISR instrument showed good agreement over Dakar than the other instruments, while CALIPSO AOD retrievals were better than those from the other sensors in Banizoumbou and Ouagadogou. The expected error bounds computed for both MODIS retrievals showed that MODISSTD consistently outperformed MODISDB in all the study sites. High AOD values were averagely observed by the satellite sensors during the local dry months (December–February), due to high concentrations of dust aerosols. High AOD values were observed during March–May, due to the condensation of water vapor on aerosol leading to increase in size and optical depth.

Atmospheric Aerosols: Some Highlights and Highlighters, 1950 to 2018 Abstract The science of atmospheric aerosols began more than a century ago; it has experienced major advancements after the mid-twentieth century with motivation from diverse public interests and concerns for environmental protection. At least six generations of mentored investigators have involvement in these advancements. Since the 1950s, important knowledge has emerged in the theory of the dynamics of suspended particles and advanced measurements. Important developments in the theory of atmospheric aerosols include: (a) nucleation and growth mechanisms, (b) formalization of particle dynamics in the Knudsen regimes, (c) characterization of the mechanisms for the particle-size distribution, (d) identification of chemical processes for atmospheric particle sources, and (e) model integration of particle physical and chemical processes with meteorological processes. Important advances in measurements have included: (a) semicontinuous determination of particle-size distributions, (b) new methods for sampling and analysis of mass concentration and composition, (c) methods for continuous characterization of aerosol chemical properties, and (d) development of direct sensing techniques using optical properties. Examples of breakthroughs in these areas are given in the text. Illustrations of achievements in each of the areas are included in the paper. The survey is completed with comments on the generational nature of investigator contributions to aerosol science.