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Title: Ventilation coefficient trends in the recent decades over four major Indian metropolitan cities
Authors: Iyer US 
Ernest Raj P
Keywords: air quality;atmospheric pollution;long-term change;metropolitan area;pollutant;radiosonde;trend analysis;urban atmosphere;ventilation;wind velocity, Chennai;Delhi;India;Kolkata;Maharashtra;Mumbai;Tamil Nadu;West Bengal
Issue Date: 2013
Publisher: Journal of Earth System Science
Indian Academy of Sciences
Source: Volume no: 122
Issue no: 2
Abstract: Thirty years radiosonde data (1971-2000) at 00 UTC for winter months over four major Indian metros, viz., Mumbai, Delhi, Kolkata and Chennai is analysed to study the trends and long term variations in ventilation coefficients and the consequences on the air quality due to these variations in the four metros. A decreasing trend in ventilation coefficient is observed in all the four metros during the 30 years period indicating increasing pollution potential and a degradation in the air quality over these urban centers. In Delhi, the ventilation coefficient decreased at the rate of 49 and 32 m2/s/year in the months of December and February, respectively during the 30-year period. In Mumbai, the average decrease in ventilation coefficient in winter months is about 15 m2/s/year whereas for Kolkata it is 14 and 17 m2/s/year in December and February, respectively. A decreasing trend in ventilation coefficient is observed in Chennai too although it is not significant. The decreasing ventilation coefficient increased the ground level pollution thereby deteriorating the air quality for the urban population. For Mumbai and Kolkata, decreasing mixing depths and decreasing wind speed contributed to the decreasing ventilation coefficient whereas for Delhi and Chennai decreasing wind speed was responsible for the decrease in ventilation coefficient. Further, the pollution potential was much higher in Delhi which is an inland station as compared to Mumbai, Kolkata and Chennai which are coastal stations under the influence of marine environment. Compared to Delhi, the pollution potential over these three metros was lower as the prevailing sea-breeze helped in the dispersal of pollutants thereby reducing their ground level concentration.
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