For the third consecutive day, Mumbai was shrouded in a blanket of smog as the overall air quality index (AQI) touched 187 on Friday morning, which is considered moderate. Since the beginning of this week, the city has been grappling with poor air quality as the AQI breached the ‘poor’ category at 199 on Tuesday, followed by an overall AQI of 182 on Wednesday.
On Thursday also, at least eight pockets of bad winds (200-300 AQI) erupted with poor air quality recorded at Colaba (288).
With the city center, as well as the extended metropolitan area, engulfed in smog for the past few days, The Indian Express spoke to experts and scientists to decode the factors contributing to the deteriorating air quality.
Low humidity, high vertical wind speed
Currently, Mumbai is experiencing dry weather, due to low humidity, but as the temperature drops, citizens are not sweating as evidenced.
According to National Institute of Advanced Sciences (NIAS) President-Professor Dr Gufran Baig, this dry or low humidity level coupled with high-speed horizontal and vertical upwelling is an important factor that causes dust to fall into the sky. City without significant elevation in ground level AQI.
Dr Baig points out that generally, when Mumbai’s humidity level is high, there are tiny droplets of water vapor in the air that piggyback on fine particulate matter (PM) and hang in the air to worsen air quality.
“However, the humidity is low in the city now because the humidity is low. Along with this, not only the horizontal wind but also the vertical wind speed – also known as eddy diffusion – is very high. This is an unusual situation. The combination of these factors, including high vertical motion, means that layers of pollution are pushed up from the surface. The layer of the pollutant cloud is pushed up until it reaches an inversion layer that does not allow it to go any higher. So the pollution cloud hangs in the atmosphere just below the inverted layer of the sky, making it appear hazy from the ground,” explained Dr Baig.
Emissions from vehicles, construction sites, industries etc
Apart from meteorological factors, Bhagwan Keshabhat said emissions from open burning, construction sites, vehicles etc. further affect Mumbai’s smog-filled air shed as pollutants from these sources are trapped in the atmosphere for longer periods during winter.
Keshabat told The Indian Express, “Apart from traditional sources such as emissions from industries and open fires, vehicular emissions have emerged as major polluting factors from construction projects, suspended particles from vehicle tires traveling to and from construction sites. Small sources like bakeries can also contribute to spoilage. “
Pointing to the sprawling metropolitan area, he added, “It is also important to look at the overall cluster of MMRs as they are all shrouded in smog and grappling with pollution. For example, in major infrastructure projects in Navi Mumbai, RMCs are not following norms. Besides, thousands of trucks ply between Mumbai and Navi Mumbai. There is a need for strict enforcement of the regulation by the authorities and they should take action against violations.”
Speaking at an event earlier this week, Mumbai’s municipal commissioner and state-appointed administrator Bhushan Gagarani said most industries comply with norms, with vehicular emissions and manufacturing activities being the biggest contributing factors for the city.
Lack of accurate AQI measurement
While the city remains under the smog layer, Mumbai’s overall air quality index ranks moderate. Some experts point out that because many of Mumbai’s recording stations are located in green areas and gardens, the stations often fail to provide an accurate picture of Mumbai’s overall air quality.
According to WMO’s international guidelines, air quality stations should be evenly distributed in different micro-environments which should include traffic junctions, downtown, residential, industrial, background, etc. Mumbai was one of the four cities that had an early warning system (SAFAR). located in India, which is said to follow those scientific guidelines. However, since the SAFAR-mobile app is non-functional, it is important to ensure that the estimated AQI includes the SAFAR reading or is based only on the average of cleaner or selected stations.
On Thursday, data from the Central Pollution Control Board (CPCB) showed that 24 of the 30 stations in Mumbai participated in providing recordings. At least 8 of the city’s 24 stations recorded a ‘poor’ AQI of over 200, while the rest dipped into ‘moderate’ air. None of the stations in Mumbai recorded ‘satisfactory’ AQI.
For perspective, AQI readings between 0-50 are considered good, 51-100 satisfactory, 101-200 moderate, 201-300 poor, 301-400 very poor and above 400 severe.
Meanwhile, records showed that PM 2.5 was the major pollutant on Thursday.
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