Akujor C. E

Bio: Akujor C. E is an academic researcher from Imo State University. The author has contributed to research in topics: Angstrom exponent & Total Ozone Mapping Spectrometer. The author has an hindex of 2, co-authored 2 publications receiving 5 citations.

Yinchuan City within Northwest China - GROUND-Based Remote Sensing Aerosol Optical Properties

Abstract: A ground-based sky radiometer was used to evaluate straight and scattering solar irradiances, as well as aureole radiances, from October 2003 to August 2004 within Yinchuan in China. Aerosol particles optical depth AOD, Angstrom exponent (ALPHA), degree size circulation, refraction index and distinct scattering albedo of aerosols were simultaneously reclaimed by means of the

Analysis on Many-year Ground Based Sunphotometer (AERONET) Aerosol Optical Properties and its Similarity with Satellite Observations in IIorin, Cape Verd, Agoufou and Banizoumbou in West Africa

Abstract: Sahelian in West Africa within Long 20 o W: 20 o E, Lat 0:30 o N through its climatic process and geographical environmental state is a major region for the distinctive of universal atmospheric aerosol optical properties. This research evaluates the spatial and secular variant of Aerosol Optical Depth AOD-441nm, aerosol particulate size categorization Angstrom exponent β 441-676nm at different four sites IIorin, Cape Verde, Banizoumbou and Agoufou. Outcomes for everyday AOD-441nm differences as well as the regular and yearly changes are presented to ascertain the aerosol climate changes in the region. We evaluated satellite resultant data of Total Ozone Mapping Spectrometer for Aerosol Index MODIS Terra and Aqua, TOMS AI with individuals of ground based Sunphotometer AERONET dimensions. Generally, presently exit good connection between ground-based AERONET dimensions and MODIS Aqua and Terra with correlation coefficients, R 2, 0.9 details in all stations. Though low coefficients low as 0.41 were ascertained in all the locations for regressions amid TOMS AI and ground based Sunphotometer AERONET data.

Influence of Dust Composition on Cloud Droplet Formation

Abstract: Previous studies suggest that interactions between dust particles and clouds are significant; yet the conditions where dust particles can serve as cloud condensation nuclei (CCN) are uncertain. Since major dust components are insoluble, the CCN activity of dust strongly depends on the presence of minor components. However, many minor components measured in dust particles are overlooked in cloud modeling studies. Some of these compounds are believed to be products of heterogeneous reactions involving carbonates. In this study, we calculate Kohler curves (modified for slightly soluble substances) for dust particles containing small amounts of K{sup +}, Mg{sup 2+}, or Ca{sup 2+} compounds to estimate the conditions where reacted and unreacted dust can activate. We also use an adiabatic parcel model to evaluate the influence of dust particles on cloud properties via water competition. Based on their bulk solubilities, K{sup +} compounds, MgSO{sub 4} x 7H{sub 2}O, Mg(NO{sub 3}){sub 2} x 6H{sub 2}O, and Ca(NO{sub 3}){sub 2} x 4H{sub 2}O are classified as highly soluble substances, which enable activation of fine dust. Slightly soluble gypsum and MgSO{sub 3} x 6H{sub 2}O, which may form via heterogeneous reactions involving carbonates, enable activation of particles with diameters between about 0.6 and 2 mm under some conditions. Dust particles > 2 mm often activate regardless of their composition. Only under very specialized conditions does the addition of a dust distribution into a rising parcel containing fine (NH{sub 4}){sub 2}SO{sub 4} particles significantly reduce the total number of activated particles via water competition. Effects of dust on cloud saturation and droplet number via water competition are generally smaller than those reported previously for sea salt. Large numbers of fine dust CCN can significantly enhance the number of activated particles under certain conditions. Improved representations of dust mineralogy and reactions in global aerosol models could improve predictions of the effects of aerosol on climate.

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.

Scattering Properties of Atmospheric Aerosols over Lanzhou City and Applications Using an Integrating Nephelometer

Abstract: The data, measured by a three-wavelength Integrating Nephelometer over Lanzhou City during the winters of 2001/2002 and 2002/2003 respectively, have been analyzed for investigating the scattering properties of atmospheric aerosols and exploring their relationship and the status of air pollution. The aerosol particle volume distribution is inverted with the measured spectral scattering coefficients. The results show that the daily variation of the aerosol scattering coefficients is in a tri-peak shape. The average ratio of backscattering coefficient to total scattering coefficient at 550 nm is 0.158; there exists an excellent correlation between the scattering coefficients and the concentration of PM10. The average ratio of the concentration of PM10 to the scattering coefficients is 0.37 g m-2, which is contingent on the optical parameters of aerosol particles such as the size distribution, etc.; an algorithm is developed for inverting the volume distribution of aerosol particles by using the histogram and Monte-Carlo techniques, and the test results show that the inversion is reasonable.

Simulation of absorbing aerosol indices for African dust : Quantifying the radiative and biogeochemical impacts of mineral dust

Abstract: It has been speculated that the vegetation change and human land use have modulated the dust sources in North Africa and contributed to the observed increase of desert dust since 1960s. However, the roles of surface disturbances on dust generation are not well constrained because of limitations in the available data and models. This study addresses this issue by simulating the Total Ozone Mapping Spectrometer (TOMS) Absorbing Aerosol Indices (AAIs) for model-predicted dust and comparing them with the observations. Model simulations are conducted for natural topographic depression sources with and without adding sources due to vegetation change and cultivation over North Africa. The simulated AAIs capture the previously reported properties of TOMS AAI as well as observed magnitude and spatial distribution reasonably well, although there are some important disagreements with observations. Statistical analyses of spatial and temporal patterns of simulated AAI suggest that simulations using only the natural topographic source capture the observed patterns better than those using 50% of surface disturbance sources. The AAI gradients between Sahara (north) and Sahel (south) suggest that the best mixture of surface disturbance sources is 20-25%, while spatial and temporal correlations suggest that the optimum mixture is 0-15% with the upper bound of 25-40%. However, sensitivity studies show that uncertainties associated with meteorology and source parameterization are large and may undermine the findings derived from the simulations. Additional uncertainties will arise because of model errors in sources, transport, and deposition. Such uncertainties in the model simulations need to be reduced in order to constrain the roles of different types of dust sources better using AAI simulation.

Radiative forcing due to dust aerosol over east Asia-north Pacific region during spring, 2001

Abstract: An optical model accounting for the East Asian dust is proposed as a result of theory calculation and composition analysis of the aerosol samples collected in China desert during the international project, “Studies on the Origin and Transport of Aeolian Dust and its Effects on Climate (ADEC)”. Study indicates that dust aerosols emitting from China deserts have smaller imaginary parts of refractive indices, therefore absorb less and scatter more solar radiation than the most dust optical models published so far. Furthermore, the forward fraction of scattering is less and the backscattering is stronger than those of the other models. The seasonal averaged radiative forcing in spring, 2001 over east Asia-north Pacific region is simulated employing the new dust optical model. The net forcing at the top of atmosphere (TOA) is estimated as -0.943 W · m^-2 for regional and seasonal mean, with shortwave and longwave contributions of -1.700 and 0.759 W · m^-2, respectively. The surface net forcing is calculated to be -5.445 W · m^-2, and made up of shortwave component of -6.250 W · m^-2 and longwave component of +0.759 W · m^-2. The distributions of TOA and surface net forcing over this region are also analyzed in this study.