Changes in the concentration and size-distribution of the sub-micron particles associated with the sea- and land-breezes at a coastal station

Surface measurements of the size-distribution of submicron aerosol particles in the range of 0.003 to 1 μm diameter have been made on 6-8 January 1998, at Thiruvananthapuram during an inter-comparison campaign of the Indian Ocean experiment (INDOEX). The results are studied with respect to the setting-in of the sea- and land-breezes at the station. Observations show an increase of up to an order of magnitude in aerosol concentrations of all size categories with the setting-in of the land breeze at 1800-1900 IST. High concentrations of aerosol particles prevail throughout the period of the land breeze at night-time. Aerosol concentrations remarkably decrease at about 1000 IST with the arrival of much cleaner air with the sea breeze. During the land breeze at night-time, the size-distributions of aerosol particles is bimodal with the maximum at 0.075 and 0.024 μm diameters. During the sea breeze, especially in the afternoon, the maximum in the accumulation mode shifts to a slightly higher size (0.133 μm) and the maximum in the nucleation mode seems to shift to a smaller size (0.013 μm or smaller). The size-distribution curves during the daytime are mostly open-ended at the small particle-size end. The enhanced coagulation of aerosol particles and the gas-to-particle conversion processes have been proposed to explain the shift of maxima in the accumulation mode and the enhanced generation of small particles in the nucleation mode in the afternoon, respectively

Background aerosol concentration derived from the atmospheric electric conductivity measurements made over the Indian Ocean during INDOEX

Measurements of the atmospheric electric conductivity on board ORV Sagarkanya during her three cruises over the Indian Ocean (17° N to 20° S, 57° E to 79° E) during the periods of December to March 1996-1997, 1998, and 1999 are reported. The results show that the values of atmospheric conductivity over the southern hemisphere are 2 to 3 times of that over the northern Indian Ocean and the north-to-south gradients extend up to the Intertropical Convergence Zone (ITCZ) and have large interseasonal and intraseasonal variations. The values of electric conductivity have been used to calculate the aerosol concentrations. The latitudinal variations of the aerosol concentration have been observed to have positive gradients from the Indian coastline to the ITCZ, and the gradients are different during the three cruises. The aerosol concentrations attain their pristine level only at 15°-20° S in this season. Because of the large interseasonal variability of the aerosol concentration observed over the northern Indian Ocean, it is concluded that estimating any secular change in the background aerosol pollution may be a futile exercise in this area

Airborne measurements of submicron aerosols across the coastline at Bhubaneswar during ICARB

Airborne measurements of the number concentration and size distribution of aerosols from 13 to 700 nm diameter have been made at four vertical levels across a coastline at Bhubaneswar (20◦25N, 85◦83E) during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) programme conducted in March–April 2006. The measurements made during the constant-level flights at 0.5, 1, 2 and 3 km altitude levels extend ∼100 km over land and ∼150km over ocean. Aerosol number concentrations vary from 2200 to 4500 cm−3 at 0.5 km level but are almost constant at ∼ 6000 cm−3 and ∼ 800 cm−3 at 2 and 3 km levels, respectively. At 1km level, aerosol number concentration shows a peak of 18,070 cm−3 around the coastline. Most of the aerosol size distribution curves at 0.5 km and 1 km levels are monomodal with a maxima at 110nm diameter which shifts to 70 nm diameter at 2 and 3 km levels. However, at the peak at 1 km level, number concentration has a bimodal distribution with an additional maximum appearing in nucleation mode. It is proposed that this maxima in nucleation mode at 1 km level may be due to the formation and transport of new particles from coastal region

[Am]Mn(HPOO): a new family of hybrid perovskites based on the hypophosphite ligand

A family of five hybrid ABX3 perovskites has been synthesized using hypophosphite (H2POO)- as the X-site ion. These compounds adopt the general formula [Am]Mn(H2POO)3, where Am = guanidinium (HUA), formamidinium (FA), imidazolium (IM), triazolium (TRZ), and dabconium (DAB). We explore the diverse structural and phase transition behavior of these materials through single-crystal diffraction measurements and demonstrate contrasting magnetism in two of the phases, Am = GUA and FA, that arises from structural distortions. The results show that hypophosphite perovskites offer a promising platform for generating new functional materials.Y.W., F.B., and A.K.C. gratefully thank the Ras Al Khaimah Center for Advanced Materials for financial support. S.S. gratefully thanks the Winston Churchill Foundation of the USA for financial support. R.M. thanks SERB, New Delhi for a JC Bose Fellowship. DFT calculations were performed at the Cambridge HPCS and the UK National Supercomputing Service, ARCHER. Access to the latter was obtained via the MCC consortium and funded by EPSRC under Grant No. EP/L000202/1. Magnetic measurements were carried out using the Advanced Materials Characterization Suite, funded by EPSRC Strategic Equipment Grant EP/M000524/1

Metal-Substituted Microporous Aluminophosphates

This chapter aims to present the zeotypes aluminophosphates (AlPOs) as a complementary alternative to zeolites in the isomorphic incorporation of metal ions within all-inorganic microporous frameworks as well as to discuss didactically the catalytic consequences derived from the distinctive features of both frameworks. It does not intend to be a compilation of either all or the most significant publications involving metal-substituted microporous aluminophosphates. Families of AlPOs and zeolites, which include metal ion-substituted variants, are the dominant microporous materials. Both these systems are widely used as catalysts, in particular through aliovalent metal ions substitution. Here, some general description of the synthesis procedures and characterization techniques of the MeAPOs (metal-contained aluminophosphates) is given along with catalytic properties. Next, some illustrative examples of the catalytic possibilities of MeAPOs as catalysts in the transformation of the organic molecules are given. The oxidation of the hardly activated hydrocarbons has probably been the most successful use of AlPOs doped with the divalent transition metal ions Co2+, Mn2+, and Fe2+, whose incorporation in zeolites is disfavoured. The catalytic role of these MeAPOs is rationalized based on the knowledge acquired from a combination of the most advanced characterization techniques. Finally, the importance of the high specificity of the structure-directing agents employed in the preparation of MeAPOs is discussed taking N,N-methyldicyclohexylamine in the synthesis of AFI-structured materials as a driving force. It is shown how such a high specificity could be predicted and how it can open great possibilities in the control of parameters as critical in catalysis as crystal size, inter-and intracrystalline mesoporosity, acidity, redox properties, incorporation of a great variety of heteroatom ions or final environment of the metal site (surrounding it by either P or Al)

Magnetic excitations in charge-ordered Nd0.5Ca0.5MnO3: A Brillouin scattering study

Brillouin scattering studies on single crystals of a charge-ordered manganite, Nd0.5Ca0.5MnO3, have been carried out for the first time. The spectra show two modes at similar to 27 GHz (B-mode) and 60 GHz (S-mode). The B-mode frequency and intensity from 300 K to 27 K, covering both the charge ordering transition at 250 K and the antiferromagnetic transition, at 170 K, exactly follow the same temperature dependence as the d.c. magnetic susceptibility. The B-mode is associated With bulk magnetic excitations and the S-mode with surface magnetic excitations of the manganite with ferromagnetic correlations. The study is strongly indicative of the presence of ferromagnetic inhomogeneities in the charge-ordered as well as antiferromagnetic phases

Studying the effects of severe Aerosol Pollution of the atmosphere on the dynamics of cumulonimbus cloud charge structure by Numerical Modeling

Studied are the effects of severe aerosol pollution of the atmosphere on the parameters of a cumulonimbus cloud (including its charge structure) and on precipitation. Considered is the example of the cloud that developed on May 11, 2009 near the town of Kharagpur (India) under conditions of severe aerosol pollution of the atmosphere due to dust transport from the desert. The in situ observations of the evolution of the cumulonimbus cloud of large vertical and horizontal extent and of its electric conditions were carried out on that day. It is found that the distribution of electric charges in the cloud was characterized by inverted polarity (i.e., the main positive charge is in the bottom of the cloud and the negative one is in the upper part of the cloud that contradicts usually observed cases). Using the small-dimension numerical model conducted are numerical experiments on the simulation of aerosol effects produced on the evolution of dynamic, microphysical, and electric structure of the cloud under study, namely, the cloud development under background conditions and in case of high aerosol concentration. It is assumed that aerosol particles possess ice-forming properties. It is obtained that the dynamic, microphysical, and electric structures of the cloud are significantly transformed under the influence of high aerosol concentrations; precipitation generation also significantly intensifies; polarity in the distribution of electric charge varies that agrees with the data of in situ observations