Review of air pollution studies in Sri Lanka

Air pollution is a growing problem in Sri Lanka mainly due to the phenomenal increase in the number of motor vehicles and traffic congestion. Regular air pollution monitoring at automated air quality stations commenced in 1997 with two monitoring stations in Colombo. Results for the period 1997-2003 showed that the levels of sulphur dioxide, nitrogen dioxide, and ozone are steadily increasing while the carbon monoxide levels are decreasing. These pollutants are below their air quality standards except for fine particles (PM10 and PM2.5) which are always above the national standard. Air quality in Kandy is worse than that of Colombo owing to its geographical location, increased vehicle population and traffic congestion. In Kandy, sulphur dioxide, nitrogen dioxide and ozone levels exceeded the standards on 41%, 14% and 28% of the occasions during the period 2001-2005. Presence of carcinogenic polyaromatic hydrocarbons from both kitchen smoke and vehicular exhausts is a definite health hazard. Mean total concentrations of 16 prioritized PAHs (PPAHs) ranged from 57.43 to 1246.12 ng/m3 with a mean of 695.94 ng/m3 in urban heavy traffic locations in Kandy. There are increasing cases of respiratory diseases such as chronic obstructive pulmonary disease due to air pollution in Kandy. Indoor air pollution involving firewood use in congested kitchens is a major health hazard and a few limited studies show that wheezing, bronchitis and asthma incidence is found in children exposed to kitchen smoke. Air quality monitoring using bioindicators is a useful low-cost method to evaluate the pollution levels and the effects of air pollution on plants and vegetation needs more attention

Complexes of 1-Hydroxyxanthone with Cu(II), Ni(II), Co(II), Mn(II), Zn(II) & Mg(II)

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Unique reactivity characteristics of Mo-coordinated S2-2 and S2-4 ligands

The synthesis of the new dithiolene complexes, [{(MeOOC)2C2S2}2Mo([mu]2-S)]-2 and [OMo(S2C2(COOMe)2)2]-, is reported. These complexes are obtained by the reaction of dicarbomethoxyacetylene (DMA) with either [(S4)Mo(S)([mu]2-S)2Mo(S)(S4)]2- or [(CS4)Mo(S)([mu]2-S)2Mo(S)(CS4)]2- and [OMo(S4)2]2-, respectively. The reaction of [(S4)Mo(O)([mu]2-S)2Mo(O)(S2)]2- with DMA results in the new dithiolene complex [{(MeOOC)2C2S2}Mo(O)([mu]2-S)]-2, which is the isomeric form of the vinyl disulfide complex obtained in the reaction of the [(S2)Mo(O)([mu]2-S)2Mo(O)(S2)]2- complex with DMA. The difference in reactivity between the two complexes that contain the same [Mo2O2S2]2+ core is attributed to the intrinsically different reactivity characteristics of the S2-4 and S2-2 ligands. As a result of Mo-S d[pi]-p[pi] bonding an alternation in the S---S bond lengths is observed in virtually all of the structurally characterized Mo-S4 units. The consequent weakening of the S---S bonds adjacent to the Mo---S bonds allows for the ready dissociation of S02 from the Mo-coordinated S2-4 ligands. This weakening also accounts for the facile formation of dithiolenes in cycloaddition reactions of alkynes with the Mo-S4 units. By comparison, the S---S bond in side-on Mo-coordinated S2-2 ligands is strengthened as a result of depopulation of the ligand [pi]*-orbitals. Reactions of the latter with alkynes do not proceed by cycloaddition. Instead, insertion into the Mo---O bond has been reported for at least one such reaction. The importance of activated polysulfide ligands in the hydrodesulfurization reaction is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26402/1/0000489.pd