. Southern Asia, extending from Pakistan and Afghanistan to Indonesia and Papua New Guinea, is one of the most heavily populated regions of the world. Biofuel and biomass burning play a disproportionately large role in the emissions of most key pollutant gases and aerosols there, in contrast to much of the rest of the Northern Hemisphere, where fossil fuel burning and industrial processes tend to dominate. This results in polluted air masses which are enriched in carbon-containing aerosols, carbon monoxide, and hydrocarbons. The outflow and long-distance transport of these polluted air masses is characterized by three distinct seasonal circulation patterns: the winter monsoon, the summer monsoon, and the monsoon transition periods. During winter, the near-surface flow is mostly northeasterly, and the regional pollution forms a thick haze layer in the lower troposphere which spreads out over millions of square km between southern Asia and the Intertropical Convergence Zone (ITCZ), located several degrees south of the equator over the Indian Ocean during this period. During summer, the heavy monsoon rains effectively remove soluble gases and aerosols. Less soluble species, on the other hand, are lifted to the upper troposphere in deep convective clouds, and are then transported away from the region by strong upper tropospheric winds, particularly towards northern Africa and the Mediterranean in the tropical easterly jet. Part of the pollution can reach the tropical tropopause layer, the gateway to the stratosphere. During the monsoon transition periods, the flow across the Indian Ocean is primarily zonal, and strong pollution plumes originating from both southeastern Asia and from Africa spread across the central Indian Ocean. This paper provides a review of the current state of knowledge based on the many observational and modeling studies over the last decades that have examined the southern Asian atmospheric pollutant outflow and its large scale effects. An outlook is provided as a guideline for future research, pointing out particularly critical issues such as: resolving discrepancies between top down and bottom up emissions estimates; assessing the processing and aging of the pollutant outflow; developing a better understanding of the observed elevated pollutant layers and their relationship to local sea breeze and large scale monsoon circulations; and determining the impacts of the pollutant outflow on the Asian monsoon meteorology and the regional hydrological cycle, in particular the mountain cryospheric reservoirs and the fresh water supply, which in turn directly impact the lives of over a billion inhabitants of southern Asia.

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Atmospheric pollutant outflow from southern Asia: a review

Metal concentration of PM2.5 and PM10 particles and seasonal variations in urban and rural environment of Agra, India

Microwave pyrolysis (MP) has emerged as a promising technique to valorize agricultural wastes (AW) into biofuels, comprising biochar, bio-oil, and syngas. To fill the research gap, we review the state-of-the-art MP conversion of AW into value-added biofuels, including the influence of feedstock composition, new reactor designs, operating conditions, catalytic applications, and reaction mechanisms. The techno-economic and environmental impacts are discussed together with key implications for future development. Microwave valorization of AW to biofuels represents an economically viable cum environmentally-benign approach by virtue of (i) high availability of AW, (ii) scalable process, (iii) great potentiality for continuous operation, and (iv) thermochemical process with positive energy ratio. For continuous MP, the microwave heating distribution, products yield, and reactor design have not yet fully explored due to the limited understanding on microwave propagation pattern, materials handling, and varying feedstock compositions. The utilization of AW as biofuels feedstock offers several environmental advantages in terms of improved biomass utilization, enhanced carbon sequestration, and lower sulphur emission. The toxicity of bio-oil can be reduced by adding metal oxide catalysts (CaO, CuO, MgO, and NiO) to lessen its content of polycyclic aromatic hydrocarbons. The process of continuous MP can be optimized by coupling shaftless auger and multiple magnetron to improve the quality of the biofuel, and uniformity of microwave heating. It is envisaged that continuous conversion of AW to biofuels is a sustainable, low carbon footprint, and alternative energy generation route, provided that the appropriate catalyst, effective condenser, and self-purging condition are chosen.

Progress in microwave pyrolysis conversion of agricultural waste to value-added biofuels: A batch to continuous approach

Receptor modeling of PM2.5, PM10 and TSP in different seasons and long-range transport analysis at a coastal site of Tianjin, China.

Recent advances in new oxidizers for solid rocket propulsion

[1] Chemical composition of near-surface aerosols at the tropical coastal location Trivandrum (8.55°N, 77°E) has been studied by analyzing the aerosol samples collected during a period of 16 months from October 2003 to January 2005. The annual mean aerosol mass loading at this site averages to around 54 ± 19 μg m−3. The chemical analysis of samples revealed Cl−, SO42−, and NO3− to be the major anionic species and Na, NH4+, Fe, and Ca to be the major cationic species. The total mass loading and the mass concentration of various chemical species showed pronounced seasonal dependence. The active aerosol sources at this location have been investigated in detail to delineate their relative dominance in different seasons. Ions like Na, Cl, Mg, and K, which are mainly of oceanic origin, showed peak during monsoon, indicating sea spray to be the most important source mechanism during the period. On the other hand, mass loading of SO42−, NH4+, PO43−, Fe, and Al and that of trace elements exhibited their maximum in winter/summer, indicating the dominance of continental/crustal sources during the period. The sea salt and non-sea salt components of individual ions like SO42−, K, Ca, and Mg also revealed distinctly different seasonal patterns. In spite of being a coastal site, the non-sea salt components dominated at this location. Dominance of non-sea salt SO42− throughout the year indicates significant anthropogenic influence at this location. On the basis of this study, a first-cut model for the chemical composition of aerosols at this tropical coastal site has been evolved.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2007JD009507

Seasonal trends in chemical composition of aerosols at a tropical coastal site of India

Chemical composition of aerosols over peninsular India during winter

Copper oxide (CuO) is an attractive burn rate modifier for composite solid propellant based on ammonium perchlorate (AP). However, the mechanism of catalytic decomposition of AP in the presence of CuO is still uncertain. Amount of gaseous products at various decomposition temperatures of AP in the presence and absence of CuO is lacking. Herein, a systematic study using thermogravimetry-mass spectroscopy (TG-MS) was carried out to evaluate the effect of CuO on AP decomposition mechanism. A novel hydrothermal method was reported for the preparation of nanosized copper oxide. The conversion of precursor Cu(NO3)2·3H2O to intermediate Cu2(NO3)(OH)3 was accomplished by in situ carbonization of small quantity of cotton fiber in the hydrothermal reaction chamber. pH of the reaction medium was controlled by utilizing the nitric acid in the reaction medium by in situ carbonization of cotton. This synthetic method aimed to minimize the shape-controlling agents and strong alkali for controlling the pH of the reaction medium for the preparation of catalyst grade CuO. Evolved gas analysis of AP decomposition products by TG-MS showed increased oxygen, chlorine and nitrogen evolution and decreased ammonia evolution in the presence of CuO, compared with that of AP without catalyst. This confirmed the enhanced interaction of ammonia and perchloric acid; the initial decomposition products of AP; and their further reaction in the presence of CuO. The change in composition of volatile products indicates change in mechanism of AP decomposition from proton transfer to electron transfer in the presence of CuO.

Salu Jacob

Papers

Seasonal trends in chemical composition of aerosols at a tropical coastal site of India

Chemical composition of aerosols over peninsular India during winter

Insight into the catalytic thermal decomposition mechanism of ammonium perchlorate

Wind-dependence of sea-salt and non-sea-salt aerosols over the oceanic environment

Adsorption performance of packed bed column for the removal of perchlorate using modified activated carbon