Smog in Chennai: Is Delhi’s air pollution the cause?

IMD and weather bloggers differ over why Chennai woke up to hazy skies, with PM2.5 levels spiking to unhealthy levels on Monday.

news Pollution

Chennai’s citizens woke up to hazy skies on Monday morning, setting off alarm bells regarding the air pollution levels in the city. With high levels of pollution in Delhi making news every other day, the smog and low visibility in Chennai caused citizens to be concerned if Chennai would go the Delhi way. This after dispersion models like SILAM (System for Integrated modelling of Atmospheric Composition) indicated that plumes of smoke were traveling east from Delhi into the Bay of Bengal, and from there blowing into Chennai and other parts of Tamil Nadu.

However, the India Meteorological Department (IMD) has categorically denied the appearance of haze in Chennai to have any connection to the pollution in the national capital. The IMD's stand is strikingly different from other weather bloggers who believe that what's happening in Delhi will soon have an impact on Chennai.

Speaking to reporters on Monday, N Puviyarasan, the Director of Regional Meteorological Centre, Chennai said that the haze in Chennai skies is due to the smog, a mixture of smoke and fog. “The cold air is coming in and there is no wind circulation. The temperature is also not high. So, when moisture comes in from the sea, it mixes with the existing pollutants in the atmosphere and causes haze. When temperature rises, the smog will go away. There is no relation between the Delhi pollution and what we see here,” he said.

According to the data available with the Air Quality Management station set up by the Central Pollution Control Board at Manali in Chennai, the concentration of particulate matter 2.5 (PM 2.5) in the air as of 2.30 pm on Monday is 127.05 ug/m3 and in Adyar the levels stood at 99.24 ug/m3, exceeding the permissible limits. According to the Indian National Ambient Air Quality Standards (NAAQS), the permissible concentration of PM 2.5 particles is 40 µg/m3 (annual average) and 60 µg/m3 (24-hour average) in industrial, residential, rural or other areas. PM 2.5 particles measure 2.5 micrometers or less in diameter and are dangerous as they are suspended in air, not weighed down, and can settle in lungs and the respiratory tract.

Incidentally, data from CPCB between October 23 until November 4 show PM 2.5 levels in Manali to be around 20 and 35 ug/m3, barring one or two days when it exceeded these numbers.

However, independent weather experts disagree with the IMD.

Weather blogger Pradeep John who runs the ‘Tamil Nadu Weatherman’ page on Facebook explains that while stubble burning by farmers in Haryana and Punjab is a recurring problem in the north, it rarely affects states like Tamil Nadu. “But this time it coincides with the break in monsoon. So most parts of tamil nadu will see hazy skies next week, thanks to the polluted air from north India being pushed down covering most of East India (sic),” he wrote.

Expanding on his post, Pradeep told TNM, that a new low pressure system has formed in the Andaman Sea which will intensify into a depression in the coming days. This he said will play a role in blowing smoke and dust from the north into the landmass over Tamil Nadu as there is an absence of the easterlies (winds blowing from the east). Instead, due to the low pressure in the Arabian Sea, westerlies or winds blowing from the western direction will push plumes of smoke and dust into the Tamil Nadu coast.

Pointing out that till date Tamil Nadu has been receiving easterlies, owing to the active Northeast monsoon from the sea and that’s why the skies were clear, Pradeep John said, “In the coming days, the sky will be hazy for at least three to four days.” He also explained that till the low pressure over Andaman Sea fizzles out or weakens, Chennai will see hazy days.

“We have already started seeing the impact of this circulation system in the air quality in Chennai. In the coming days, the pollution levels will be more than today (Monday). We will be having a little increase in pollution levels, but not in the scale of what is going on in Delhi,” he added.

Santhosh Krishnan, who goes by the name Coimbatore Weatherman also confirms to TNM that in the coming days, coastal Tamil Nadu, particularly Chennai will see a significant increase in the pollution level due to impact from Delhi’s pollution. “Interior Tamil Nadu might not feel the impact much, but Chennai definitely will. The AQI might even go upto 200-300 in the coming days,” he warned.