Delhi is one among the highly air polluted cities in the world. Absence of causal relationship between emitting sources of PM and their impact has resulted in inadequate actions. This research combines a set of innovative and state-of-the-art analytical techniques to establish relative predominance of PM sources. Air quality sampling at six sites in summer and winter for 40 days (at each site) showed alarmingly high PM concentrations (340 ± 135 μg/m). The collected PM was subjected to chemical speciation including ions, metals, organic and elemental carbons which followed application of chemical mass balance technique for source apportionment. The source apportionment results showed that secondary aerosols, biomass burning (BMB), vehicles, fugitive dust, coal and fly ash, and municipal solid waste burning were the important sources. It was observed that secondary aerosol and crustal matter accounted for over 50% of mass. The PM levels were not solely result of emissions from Delhi; it is a larger regional problem caused by contiguous urban agglomerations. It was argued that emission reduction of precursors of secondary aerosol, SO, NO, and volatile organic compounds, which are unabated, is essential. A substantial reduction in BMB and suspension of crustal dust is equally important to ensure compliance with air quality standards.
A TiO 2 -based photocatalytic oxidation study of volatile organic compounds (VOCs: benzene, toluene, ethylbenzene, and xylenes) requiring close monitoring of the catalyst coating, its deactivation, and regeneration was undertaken. For all experiments, the effectiveness of sol−gel coating of nanosized TiO 2 particles (on a glass cylindrical reactor) in terms of the surface morphology, film thickness, and band-gap energy was ensured for obtaining a consistent reactor performance. The estimated VOC degradation rate constants (range of 1.16 ± 0.06−1.79 ± 0.05 min −1 m −2 ) were comparable or higher than those reported in the literature. Reduction of the degradation rates [48% (o-xylene) and 59% (toluene) over a 13 h operation period] with successive deterioration of the catalyst surface appeared to be a major challenge both for design of the reactor and for its long-term operation. A set of definite suggestions has been made for design criteria (degradation rate) and the frequency and method of catalyst regeneration for long-term field operations.
Photo-catalytic degradation of volatile organic compounds [VOCs: benzene, toluene and p-xylene (BTX)] was investigated using a batch reactor having a TiO 2 (catalyst)-coated aluminum sheet and a source of UV light (sunlight or UV lamp). To study the photo-oxidation, experiments were conducted under the following configurations: (1) TiO 2 (m): microparticle (0.32-3.31 lm) and sunlight (2) TiO 2 (n): nanoparticle (0.80-4.70 nm) and sunlight, (3) TiO 2 (m) and UV lamp and (4) TiO 2 (n) and UV lamp. Degradation of BTX followed first-order decay for individual compounds. The degradation rate constant in min -1 cm -2 (coated surface area) was the highest for configuration (4) (benzene 1.07 9 10 -3 , toluene 1.36 9 10 -3 and p-xylene 2.93 9 10 -3 ) followed by configuration (2), thus indicating the importance of particle size of the catalyst in degradation. Degradation of BTX mixture did not follow first-order decay. Benzene was an intermediate product of oxidation of toluene. Benzene and toluene were intermediate products of oxidation of p-xylene. For degradation of BTX mixture, a mathematical model was proposed to predict concentrations as a function of time. Experimental and model results showed similar trends in BTX degradation. The model accounted for increases in mass of toluene and benzene due to the degradation of p-xylene.
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