Ventilation coefficient trends in the recent decades over four major Indian metropolitan cities

Abstract

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 m 2 /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 m 2 /s/year whereas for Kolkata it is 14 and 17 m 2 /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.

Personal exposure to fine particulate matter concentrations in central business district of a tropical coastal city

“…The mixing height was observed to vary diurnally, with comparatively low mixing height in the night and morning (Mehta et al 2016). It was also reported that the reason for the occurrence of high pollution potential was due to low mixing height (less than 500 m) and mean wind speed less than 4 m/sec during the morning hours (Gross 1970;Iyer and Raj 2013). Thus, morning hours with high traffic flow and less wind speed can result into poor air quality.…”

Analysis of ambient formaldehyde in the eastern region of India along Indo-Gangetic Plain

“…The percentage gradually decreases with an increase in mixing ratio range and reduces to a value of~1 % at mixing ratios greater than 600 ppbv. Further, a breakup of distribution of upto 100 ppbv is also provided in the Ventilation coefficient is used to determine the air quality and pollution potential of a region (Iyer and Raj 2013).…”

The Development of Boundary Layer Structure Index (BLSI) and Its Relationship with Ground Air Quality

“…Convective ABL height is referred to the height where the potential temperature begins to increase and stable ABL height is designated as the height where the first important vertical potential temperature gradient variation takes place [35]. Ventilation index (VI) provides information about the ventilation ability of the ABL [28,29]. The equation for the ventilation index following Pasch et al [36] is as follows: Diagrams for stable energy.…”

“…Likewise, both the CAPE and the E W parameter consider the ability of the boundary layer (BL) atmosphere to diffuse air pollutants from a thermodynamic point of view but does not consider the horizontal removal ability of wind speed. Therefore, many authors have alternatively used the pollution coefficient P i [26,27] and ventilation index (VI) [28,29] to study the relationship between pollution and wind. However, both P i and VI consider the ability of the boundary layer atmosphere to diffuse air pollutants from a kinetic point of view and do not consider the vertical diffusion capacity of the BL.…”