New Delhi: The Nitrogen Dioxide (NO2) emission levels, a gaseous pollutant classified under the highly reactive nitrogen oxides (NOx) is a ‘pollutant of concern’ for the South Asian countries, according to the State of Global Air (SOGA) South Asia Regional Snapshot on Air Quality. The report released on September 12, highlighted that India stood second after Bangladesh, in 2019, to have the second highest NO2 emission levels, with 40 parts per million, surpassing the World Health Organization (WHO) guideline of 10 parts per million. The other two countries with high NO2 emission levels included Nepal and Pakistan. The report stated that NO2 continues to be an important environmental health risk for these countries.
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Causes of High Nitrogen Dioxide Emission Levels
Talking about the report, Executive Director of Research and Advocacy in Centre for Science and Environment (CSE) and report reviewer, Ms Roychowdhury, said,
Conventionally, we have been focusing on the particulate matter (PM2.5 levels) in our cities, which is very important. But what we have been beginning to understand is to focus on the gaseous emissions that give rise to the PM2.5 levels, especially Nitrogen Dioxide. Gases like NO2, once they are out in the air, they go through atmospheric changes, and form secondary particles. It further reacts with other gases and forms nitrate particles. With the formation of nitrate particles, the same gas is adding to the particulate pollution load and increasing the PM2.5 levels.
The major rise in the NO2 emissions is fuelled by an increase in vehicle ownership, Ms Roychowdhury said. NO2 gets in the air from the burning of fuel, and it forms from emissions from cars, trucks and buses, power plants, and off-road equipment. NO2 is often used as a marker for traffic-related air pollution, which is turning out to be one of the highest in the Indian cities, she said. She further said,
So, more vehicles mean high NO2 emissions, hence, increase in the PM2.5 levels.
Apart from NO2, rapid energy production, industrialisation, population growth, increase in transportational activities, and agricultural waste burning are also the reason behind the rise in the PM2.5 levels, she added.
Dr Sarath Guttikunda, founder and Director of Urban Emissions, said that NO2 catalyses reactions between different gases in the air that further forms an ozone layer. Talking about significance of mitigating NO2 emission levels, Dr Guttikunda further added,
If you compare the overall NO2 levels of India or other South Asian countries with other regions of the world, the levels are still lower. But the rate of increase is higher in the country because the number of vehicle ownership is growing in the absence of technology to control the NO2 emissions. If this is not taken care of, NO2 will not only have a health impact, but also add to the particulate pollution and increase the ozone pollution.
Health Impacts of Nitrogen Dioxide
High levels of NO2 give rise to the production of particulate matter (PM) and ozone, another gaseous pollutant harmful to health. It can lead to chronic respiratory illnesses, severe asthma symptoms, and impaired lung development among adults and children, the report stated. Ms Roychowdhury said that NO2 can also lead to Chronic Obstructive Pulmonary Disease (COPD) and is also responsible for sudden death syndrome among children.
How Can Countries Reduce The Gaseous Pollutant NO2?
Highlighting the efforts made by India, Ms Roychowdhury said that India has a policy of emission standards in place – Bharat Stage Emission Standards (BS Norms), which focuses on reducing nitrogen dioxide emissions by vehicles, but it has not reached the desirable levels.
Under Bharat Stage Emission Standards Norms, we have leapfrogged from Bharat Stage IV (Euro IV equivalent) to Bharat Stage VI (Euro VI equivalent) that aims at reducing the nitrogen oxides (NOx), particulate matter (PM), and hydrocarbons (HC), but there is a long way to go. We need better monitoring systems.
The report has emphasised the need for countries to drive more attention towards reducing NO2 emissions and introduce stringent policy programmes addressing transportation emissions, clean energy, and the burning of agricultural waste, among others.
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