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Updated: Nov 07, 2019 23:20 IST

New Delhi: There was a spike in air pollution levels in eastern and southern India on Thursday with the Air Quality Index (AQI) in some parts of Chennai touching 300 over the past 24 hours. Officials said that this was primarily because winds were carrying pollutants from the northern plains towards the Bay of Bengal and local poor dispersal of pollutants.

A Central Pollution Control Board (CPCB) official, who did not want to be named, said that north-westerly winds have blown the smoke created because of stubble burning in Punjab and Haryana from the northern plains because of a developing cyclonic depression over the Bay of Bengal.

Pollution spikes are common in the first half of November in northern India as farm fires peak in Punjab and Haryana during this time and the resulting smoke settles over the region. Farmers often burn stubble left behind after harvest as a quick and cheap way of clearing their fields for the next round of sowing.

The air quality in Delhi was reduced to its worst level since 2016 on Sunday as the AQI sharply rose to a severe level of 494. Severe air pollution can worsen existing respiratory illnesses and also affect even healthy people.

The CPCB’s real-time monitor showed the AQI crossing the 300-mark in some parts of Chennai. The average AQI of Chennai was 272, almost double the level on November 2. Odisha’s Talcher recorded the highest AQI in the country--413.

The air quality is considered good when the AQI is below 50 and satisfactory when it is under 100.

The AQI in Andhra Pradesh’s Visakhapatnam and Vijayawada rose to 224 and 204—from 252 and 197 last Saturday. The AQI in Kolkata was 215 while it was 317 a day earlier. The pollution levels dipped in Bangalore with the AQI being 156 compared to 165 on Wednesday because of the local weather conditions.

An India Meteorological Department (IMD) official said that the cyclonic storm, which is expected to make landfall on Friday, is preventing pollutants from dispersing over the Bay of Bengal as it is moving towards the eastern coast.

“In fact, strong inward winds from… [the Bay of Bengal] have pushed the winds carrying the smoke towards south from eastern India…,” an IMD scientist said.

The CPCB scientist quoted above said that the pollution levels in southern and eastern cities have also increased because of the local factors like emissions from vehicles but the spike was because of the winds carrying the particulate matter.

Air Visual Earth, which tracks the wind movement of particulate matter pollutants, showed that the spike in southern cities was because of winds carrying pollutants from the northern plains.

The CPCB scientist cited above added that the situation is likely to improve in a day or two because of change in wind direction. The impact of the depression in the Bay of Bengal will also end with heavy rains, which is also expected to bring some respite.

Officials said that unlike in the northern Indian plains, the air pollution monitoring in eastern and southern India, considered to be comparatively cleaner, is less common. For instance, Kolkata has only seven monitoring stations, Chennai four and Visakhapatnam one. Delhi has 38 pollution monitoring stations.

Environmentalist Nityanand Jayaraman said that Chennai’s air pollution has worsened due to growing vehicles, three harbours, thermal power plants and oil refineries. “The wind blowing from...[north India] is also causing pollution in Chennai...,” he said.

Environmentalist E A S Sarma said that the CPCB declared Visakhapatnam “critically polluted” and imposed a moratorium on new industrial projects in 2014. “The moratorium was lifted under pressure from politicians [in 2017],” he said.

Raj Bhagat Palanichamy, a remote sensing analyst with the World Resources Institute, too, blamed the farm fires’ smoke for the rise in pollution levels in eastern and southern India. “The Atmospheric Dispersion Modelling System [used to calculate concentrations of pollutants] shows that the plumes of the smoke have reached southern India,” said .

The rising pollution prompted Bihar chief minister Nitish Kumar on Wednesday to order the phasing out of diesel and old petrol autos. He also ordered a revamp of the public transport system as the AQI in Patna rose to 414 on Wednesday. The AQI came down to 347 on Thursday, which still comes under the “very poor” category.