Here’s how the link of air pollution between La Nina and stubble burning

While meteorologists are expecting an intense winter as another La Nina appears for the second year in a row, severe air pollution is also expected in the coming months in northern India. In October, even though lesser number of stubble burning incidents and widespread rain and snow kept pollution under control, the situation seems to be changing now.

Pollution levels are again in the ‘very poor’ and ‘hazardous’ categories in most cities in the Indo-Gangetic plains (IGP) due to fall in temperature and other meteorological factors, such as slow wind speed and direction . Seasonal factors such as firecrackers and stubble burning have, as always, compounded the problem, as the highest level of crop residue burning coincides with Diwali.

The link between La Nia and air pollution
With La Nina for the second time in a row, North West India is gearing up for severe cold weather this season. Meteorologists are predicting record low temperatures across the IGP this year, with colder-than-normal temperatures expected in November and December. Temperatures in India are expected to drop by as much as 3 °C (37 Fahrenheit) in January and February, before recovering, in some northern regions, according to a recent Bloomberg report.

“There is a high probability of a second La Nia, which may result in extreme cold from December 2021-February 2022. The peak of oceanic events is expected during this period. It should be noted that winter The intensity is also influenced by many other factors such as decreases in other parts of the world,” said GP Sharma, president-meteorology and climate change, Skymet Weather.

It has been clearly established that winter season is a favorable time for increase in pollution. During winters, cold air often settles over northern India. The reversal of winter temperatures contributes to the formation of haze. This reversal of temperature occurs when cold air is trapped under a layer of warm air. Since cold air cannot rise above warm air, pollution remains in cold air as long as the temperature is inverted. The haze seen in the winter months is mostly also a result of the inversion of temperature. Generally, the air high in the atmosphere is cooler than the air near the surface of the Earth. Warm air rises near the surface, spreading pollutants from the surface into the atmosphere.

More intense periods of pollution in the Northwest Plains
The possibility of more cold days in the weather will certainly lead to more number of ‘poor’ to ‘severe’ air quality days for the entire IGP, especially Delhi NCR. Experts point out that the winter season is already conducive for pollution and a further fall in the mercury will worsen the situation.

“With the fall in temperature, more stable conditions are likely. However, this is assuming that the winds do not change. If for some reason the winds slow down and there is an increase in stubble or biomass burning during this period, the overall air quality situation over the northern plains, including New Delhi, may worsen. In short, all while remaining stable, and freezing conditions prevent vertical mixing within the atmosphere. Hence, the possibilities for poor air quality are high,” said Dr. V. Vinoj, Assistant Professor, School of Earth Ocean and Climate Sciences, Indian Institute of Technology Bhubaneswar.

Smog Circle
Cold days can trap the plains in very bad smog circles, which means that the days of poor air quality will be frequent. Professor S.N. Tripathi, Head of Department – Civil Engineering, IIT Kanpur and Steering Committee Member, National Clean Air Programme, MoEFCC pointed out that particulate matter (PM) changes its property after exposure to fog, paving the way for more fog. Is.

“Surely, the intense winters will make the situation worse. This would mean a higher amount of haze which would increase the trapping of available pollutants on the surface. This can lead to a build-up of smog which can make the situation worse. All these situations will result in a smog vicious cycle in which we will not see the evacuation for several days. Also, cooler weather is associated with relatively higher humidity, which makes particulate matter (PM) more likely to hold more water. After the fog disappears, the water vapor or droplets evaporate, leaving behind the PM. But a very small chemistry works here and thus the PM does not remain the same. By that time it becomes more oxidized. There is a stronger association between oxidized PM and fog condensation nuclei than between non-oxidized components. In fact, the droplet oxidizes faster and the oxidized PM is more efficient and thus fog formation will be much easier compared to the previous day,” Dr Tripathi said.

The only way is to reduce emissions
Scientists have warned to be extra careful this season as the weather is out of control and thus the focus remains on reducing local emissions.

“We have to be more cautious this season, as the pollution can get worse during the cold season. Whatever excess we see can only be offset by reducing emissions, at least at the regional level. But if we continue to emit the same amount with adverse meteorological conditions, there could be some significant increase in pollution levels in the coming season. October has been good in terms of pollution due to extended monsoon rains and less stubble burning. Although the pollution was low, it was still above the permissible limits. December and January are the main winter months and we do not expect stubble burning during that time. With the prospect of record low temperatures, we are left with no other option but to reduce emissions. Otherwise mixing all together the effect will increase manifold and pollution will increase manifold. We have no control over meteorological conditions, but we can control emissions,” said Dr. Sagnik Dey, Associate Professor, Center for Atmospheric Sciences, Indian Institute of Technology-Delhi and Coordinator, Center of Excellence for Research in Climate Change and Air Pollution (CERCA).

Burning straw, falling mercury will worsen air pollution in Delhi-NCR
Delhi-NCR is heading towards some worse air quality days. On-and-off rains during October extended the peak stubble burning season and far fewer farm fires were reported in the month than in 2020.

Data from ICAR-Indian Agricultural Research Institute shows that total incidents of crop residue burning in six states this year have been recorded 54.8% less than the corresponding period in 2020. As a result, most of the cities in these six states have recorded lower concentrations of PM 2.5 in September and October 2021 as compared to the previous year. Similarly, for the months of September and October in the last five years, NASA has received information about Punjab, Haryana and U.P. Calculation of average fires in the U.S. shows that the average PM 2.5 level in Delhi was the highest in 2017, when the average number of fires was also the highest.

However, biomass burning has now started gaining momentum. Incidents of crop residue burning have increased significantly, especially in the north-western plains. In fact, the above data shows that Haryana has already surpassed the number of cases reported last year, followed by Uttar Pradesh which is rapidly rising near the 2020 count. Looking at the trend in other states, Punjab is likely to pick up pace in the coming days. Experts expect the next two weeks to be crucial for Delhi’s air quality as the chances of stubble burning in the Indo-Gangetic plains peak.

Also, changing weather patterns due to climate change are also contributing to the increase in air pollution in this season. Monsoon 2021 had an extended stay in the country, and began its withdrawal only after 6 October, which was 20 days from the normal date of onset of withdrawal of monsoon. The presence of monsoon continued to rain over the north-western plains till October 24, pushing the stubble burning season as well as the polluted days to November.

Now as we enter November, the combination of fall in mercury and decrease in wind speed will put Delhi-NCR in a tight spot in the coming days. “If the peak of stubble burning was observed in October, the impact on Delhi-NCR would have been less. Neither the wind speed would have been slow nor the temperature would have been so low. But November is a transition month from spring to winter, in which we will see a drop in temperature as well as wind speed. This sets a stage for days of unhealthy air quality for the national capital with the onset of winter,” said Mahesh Palawat, VP-meteorology and climate change, Skymet Weather.

Council on Energy, Environment and Water (CEEW) expert Tanushree Ganguly, program lead and L.S. Kurinji, Program Associate has warned of some tough days ahead for Delhi-NCR. “Earlier this season, the number of daily fires in Punjab and Haryana was less than 1000. But in the last four days, more than 2000 fires were reported per day in Punjab and Haryana. As we are in the peak of burning, 3000-4000 fires per day are likely to occur in the coming days. This can increase the impact of stubble burning on the air quality of Delhi with adverse meteorological conditions like falling temperature, drop in wind speed.”

He further added, “While the current share of stubble at the particle level of Delhi is less than 10 per cent, it is expected to reach 35-45 per cent on November 5 due to north westerly winds. Also, since Diwali this year peak stubble burning.” As time goes by, SAFAR’s forecast suggests that the additional load from firecrackers could further degrade the air quality in Delhi NCR. Therefore, it is important for Delhi NCR to prevent unhealthy AQ conditions.

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