On the morning of February 8, the participants in the first-ever G-20 Youth Summit woke up in the morning in Guwahati and were thought as if they were in Delhi NCR. It was because of a haze that covered the sky, somewhat unusual in this region. Yes, Assam’s largest city Guwahati was engulfed by a thick blanket of dust on February 8, reminding its citizens of the hazy sky often seen in Delhi NCR during the winter.
The skyline in Assam’s biggest city and the hub of the entire Northeast was filled with thick dust as the Air Quality Index (AQI) turned ‘poor’. Apparently, the reason was the prolonged dry spell and innumerable construction works which have been on for the development of the city in the last two years or so. With the construction of flyovers, bridges and roads going on in every part of the city, along with countless private constructions, the city has been suffocating for quite some time with hazardous air in the last several years. The Air Quality Index of Guwahati recorded on that day was 244 AQI, which falls in the ‘poor category’.
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The Enforcement Branch of the Guwahati Municipal Corporation (GMC) conducted a drive on February 6 which entailed vigorous and surprise checks at several construction sites in and around Guwahati city amid the plummeting air quality levels. According to reports, the residuals of the different constructions, ranging from the Brahmaputra Riverfront Development construction to the construction of drains, buildings, and flyovers have been one of the main factors in the plummeting AQI in the city. The poor Air Quality of Guwahati has come close to the poor Air Quality in Delhi which dropped to 245 AQI in January this year.
Usually, the air quality at Assam starts deteriorating in late October. The winters are the worst-hit season in terms of air pollution. However, the worsening air pollution in Assam is a worrying factor and currently, 31,205,576 people in the state are breathing toxic air that does not meet WHO’s clean air guidelines. The real-time air quality in Assam as on 12 pm on February 11 was 118 AQI (poor). The current concentration of PM2.5 in Assam on that day was 62 (µg/m³). The World Health Organization (WHO) recommends 15 µg/m³ as the threshold concentration of PM2.5 for 24 hours. February 11, the concentration was 2.48 times the recommended limit.
The primary causes of outdoor air pollution are solid, liquid particles called aerosols and gas from vehicle emissions, construction activities, factories, burning stubble and fossil fuels and wildfire, etc. For Guwahati, it is mostly the construction activities and vehicle emissions. According to the data from the District Transport Officer, Kamrup Metro, there were over 3,77,211 four-wheelers and 6,38,946 two-wheelers in Guwahati city in the year 2020-21. There was also a 14% rise in the registration of vehicles in the same transport office in 2021.
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The myth of a pristine sky with pure air in the ecologically sensitive region has long gone past. Experts have already warned about the increasing air pollution in several cities of India’s northeast region and Guwahati has topped the list. The problem of air pollution has been growing steadily in this region with worsening air quality. But the public attention it deserves has not been equally adequate.
According to New Delhi-based Centre for Science and Environment in its report in 2021, Guwahati’s annual average of PM2.5 level has constantly been much higher for the past three years compared to the national average. While the annual average level of India has been 40 micrograms per cubic metre (ug/m3) for the past 3 years, the annual standard of PM2.5 level of Guwahati has been 56 ug/m3 in 2019, 62 ug/m3 in 2020 and 60 ug/m3 in 2021. “The city’s average is considerably below the annual standard,” CSE commented in its report.
Despite Low Annual Levels Weekly PM2.5 levels increase during the winter months. Although the annual average of Guwahati is 60 ug/m3, it reached its worst in the week ending on January 17, 2021, when it was 189 ug/m3; the worst of winter 2020-21. For the present winter season of 2021-22, the worst level was recorded in the week ending on November 7, when the weekly PM2.5 level reached 78 ug/m3.
The NO2 concentration increases with the evening traffic rush in cities, peaking especially from 6 pm. The NO2 in Guwahati increases five-fold hourly between 1 pm and 6 pm. The city also has a morning NO2 peak from around 7-8 pm, but it is relatively lesser compared to the evening peak. The night-time NO2 is also high, indicating the impact of night-time truck movement in the city. The CSE study found that there is a significant increase in the amount of NO2 in the NE region during November as compared to October and September 2021. In 2020, the NO2 level in Guwahati had increased with the incoming of winters with an 85 per cent jump in monthly NO2 levels between September and November. However, the city’s NO2 data was found to be almost flat since May 2021. Comparing the data of the previous years and the other NE regions, CSE concluded that “there seems to be a problem with the monitors”.
Bursting crackers on Deewali nights also contributes to the choking air quality in Guwahati. Despite directives by the Pollution Control Board of Assam to burst only green firecrackers from 8 pm to 10 pm, widespread flouting of the 2-hour firecracker bursting window caused the Air Quality Index (AQI) for PM 2.5 to stand at 213 on Deewali night in 2021 while the earlier AQI was 110, according to the data published by Central Pollution Control Board.
The air quality in Guwahati dropped from Moderate to Poor post-Diwali celebrations. The Supreme Court has completely banned the bursting of firecrackers containing Barium salts and only green firecrackers are allowed to burst for two hours. During 2020-21 Guwahati recorded the greatest pollution build-up on Deewali night, with a 3.6-fold increase in the night-time (8 pm-8 am) PM2.5 levels, compared to the average level recorded seven nights ahead.
The CSE report concluded that Guwahati has had a stable annual average of PM2.5 level since the last three years of its assessment period, but it does not meet the annual standard for PM2.5. In order to meet the standard, the city needs to cut its pollution level by 33 per cent. According to the analysis, the most polluted months for the city have been December and January.
Analysis of days as per the categorization of the national AQI shows that the city is experiencing an increasingly higher number of days with poor or worse air quality, most of which are from the winter months. The number of days with good air quality has remained the same in the last two years. In 2021, the number of days with air quality in the ‘very poor’ or ‘severe’ categories stands at 54 in Guwahati till December 7, 2021. However this time the poor AQI is recorded in February.
In a relatively small town like North Lakhimpur in Assam, the Ambient Air Quality Date under NAMP was 102.00 (PM10 (g/m3)), 5.25 (SO2(
g/m3)) and 13.25 (SO2(
g/m3)) as on February 26, 2021(APCB).
Research conducted by the Indian Institute of Technology (IIT), Kanpur found a link between air pollution and intense rainfall recently. Analysing long-term satellite data between 2002 and 2016 and modelling to understand the association between aerosols and cloud properties, the study found that air pollution particles lead to changes in the physical properties of monsoon clouds, which can lead to more intense rainfall, flash floods and unusual gaps in the progression of monsoon rainfall (Nature). “Not all extreme rain events can be linked to aerosols as other meteorological factors also play a role, but cases of extreme and erratic monsoon rainfall in inland areas affected by air pollution may be linked to this phenomenon,” says the study.
Aerosols, particularly black carbon and dust particles, induce “cloud invigoration”, which means cloud cover and thickness increase because of the reduction in the size of cloud droplets and other structural modifications during cloud formation. Enhanced cloudiness reflects more sunlight back to space, leading to a cooling effect on the clouds’ surface. Apart from cooling, air pollution-induced cloud properties can also be linked to intense rainfall.
It also facilitates thunderstorm-type clouds that have an umbrella-type structure. This umbrella structure stops solar radiation and creates a cooling, which causes a delay in the arrival of the next thunderstorm. This leads to episodes of intense rain followed by breaks in progression, the study says.
Aerosols, whose main sources are fossil and bio-fuels combustion from the residential and industrial sector, and biomass burning absorb solar radiation, such as soot, causing these disturbances. Air pollution can affects health and the World Health Organization estimates that it caused 3.7 million premature deaths worldwide in 2012 alone. But now another recent study shows that air pollution can trigger floods as well. In July 2013, heavy rainfall resulted in a catastrophic flood in the Sichuan Basin, a mountainous area of China.
Nearly 2.5 feet of rain fell in just five days which led to the findings that air quality played a role in the valley’s disaster. It was found that in some geographic regions, aerosols absorb heat from the sun, suppressing the chance of rain during the day and stabilizing the atmosphere. At night the warmed, rising air is transported to mountainous areas before it heads higher up into the atmosphere. This causes massive precipitation that can actually make flooding worse (Fan, J., et al. (2015).
Air pollution from soot and aerosol emissions is also making cyclones over the Middle East and South Asia more destructive. Natural differences in wind speed and direction over different heights in the atmosphere, known as ‘wind shear’, normally keep cyclones in check—effectively tearing the storms apart before they reach a certain size. But emissions from sources such as biomass burning and diesel vehicles have interfered with wind patterns, reducing wind shear and enabling cyclones to grow twice as intense, according to a study published in Nature last week (3 November).
Cyclones that occurred between 1997 and 2010 were up to three times more intense than those between 1979 and 1996. It may be recalled that five of the strongest storms during the period occurred after 1998. Aerosol emissions in the region have also grown six-fold since the 1930s, creating a three-kilometre-thick layer of pollution over the Indian Ocean, known as the South Asian atmospheric brown cloud, which absorbs sunlight, causing the ocean to cool and affecting wind circulation.
According to a report by the Pollution Control Board of Assam (PCBA) in 2015, Guwahati has one of the highest Black Carbon pollution levels in the world. The city’s PM2.5 concentration is more than eight times the WHO standards. Transport and dust are the primary contributors. It is due to the rapid urbanization and poor environmental quality control in Guwahati which is giving rise to such high Black Carbon levels. Though Assam does not have heavy industries the entire state is moderately polluted air.
On July 21, 2019, leading doctors of Assam and other North-Eastern States join the movement for the launch of Doctors for Clean Air—a campaign for raising awareness about the increasing air pollution and its health impacts in the region. Besides health risks, air pollution is the likely cause of abnormal monsoons and heavy rains and thunderstorms compounding the already existing flood problem of Assam.
The studies on atmospheric simulations in Sichuan Basin show that if current industrial emissions are reduced to a level before China’s economic boom, less precipitation (up to 60% lower) could be predicted. This is due to the weakening of the “aerosol-enhanced conditional instability” mechanism. This suggests that air pollutant reduction can effectively mitigate floods in that area. This discovery is also called “aerosol-enhanced conditional instability,” and its flipside is that reducing pollution in places like Sichuan can actually reduce floods. As pollution particles worsen flooding, it could help future weather forecasters predict floods.
In Guwahati industrial emission contributes only 5.29% of PM2.5 concentration in the air. The major contributor has been transporting (36.5%) and dust (27%). To reduce the presence of aerosols in the atmosphere vehicular emissions require considerable control. A new and effective vehicle policy is very essential to mitigate the increased threat of flood caused by air pollution. Green technology in the transport sector, mostly the adoption of electric vehicles should be seriously considered to control the aerosol-induced precipitation and also to make Assam a climate-resilient state. Opting for public transport from private vehicles and shifting public transport to electric power from fossil fuel could contribute effectively to achieving the desired goals to mitigate floods and climate change.
For this Guwahati and other cities in the region desperately need a robust air quality monitoring and pollution control mechanism. But the Pollution Control Board of Assam (PCBA) does not have sufficient devices to measure the PM2.5 level of AQI. The PCBA for long took the stand that Guwahati along with the rest of Assam receives more dust from the river banks and roads during the winter season.
The Northeastern states need urgent attention and support under the National Clean Air Programme to implement locally appropriate clean air action and a robust air quality monitoring network for proper risk assessment.