Nitrogen Dioxide: A growing health hazard for Dhaka

Nitrogen dioxide has become a cause for serious concern as the concentration of the pollutant in Dhaka's air is increasing while it is decreasing across the world, according to a global study.

This pollutant has implications for the production of "ozone" — another gaseous pollutant that can be harmful to human health, as well as the formation of particulate matter, said the study titled "State of Global Air: South Asia, A Regional Air Quality Snapshot."

The flagship study, conducted by the US-based organisation Health Effects Institute, said exposure to NO₂ can irritate airways, aggravate existing respiratory diseases, raise the risk of asthma development in children, and increase the frequency and severity of asthma symptoms in children and adults.

"South Asia is among the few regions in the world where NO₂ levels are increasing in some areas. Between 2000 and 2019, NO₂ exposure in South Asia increased by 22 percent, while global averages decreased by 5 percent," said the report published last night.

Data shows that in 2019, five cities in Bangladesh were among the top 20 cities with the highest NO₂ levels in the region.

The cities exceeded the WHO Annual Air Quality Guideline for NO₂ (10  µg/m3), with Dhaka having the highest level in the country at 23.6 µg/m3, followed by Chattogram with 21.3 µg/m3, Sylhet with 13.5 µg/m3, Rajshahi with 13.1 µg/m3, and Khulna with 11.0 µg/m3.

Meanwhile, Kathmandu (Nepal), Hyderabad (India), Bengaluru (India), and Karachi (Pakistan) had the highest NO₂ levels in the region, in that order.

The report said a total of 31 percent of fine particulate matter (PM2.5) in the region comes from residential sources, including the use of solid fuels for heating and cooking.

Additionally, a growing fleet of personal vehicles and continued reliance on coal for energy production pose the challenge of increasing levels of NO₂ and PM2.5, said the report.

Explaining the reason for the rise of NO₂, the report said this increase is likely driven by a reliance on fossil fuels for energy production, expanded industrial activity, and increases in the number of vehicles over the last decade.

As many as 564,739 vehicles were due for regular fitness checks but did not take clearance as of April 30, according to Bangladesh Road Transport Authority data.

More than 50 lakh vehicles are plying the streets, and most of them are old.

Experts said that incompetent combustion of fuel, old and unfit vehicles, and low-quality fuel are the key reasons for the rise of NO₂ levels in the air.

Prof Abdus Salam of Dhaka University's chemistry department said old vehicles and traffic congestion are the key sources of NO₂, which can be checked by using clean energy and allowing only fit vehicles on the roads.

"As the usage of cars increases, the combustion of fossil fuels is also on the rise, as is the concentration of nitrogen dioxide in the air," he said.

When asked whether the government is taking any steps to reduce it, he said "One may find something on paper but in reality, there is nothing."

Government officials said they know the sources of the air pollution, but to address the problem, a holistic approach is needed.

Department of Environment officials said that the air quality improves in the rainy season in Bangladesh due to showers, but in recent years it has been observed that the air quality remains poor even in the rainy season too.

"Over the years, vehicles have become a major concern for air pollution in the big cities, and that's why we see that air quality does not improve at an expected level in the rainy season," said DoE Director Md Ziaul Haque.

He also said the BRTA does not have any mechanism in place to do emission tests on the vehicles, and vehicles that are 25 years old must be taken off the road.

The report said air pollution is the leading environmental risk factor for poor health in South Asia.

At the population level, the disease burden of air pollution can strain healthcare systems and have a broader impact on communities and economies, it added.

Speaking on the matter, Dr Pallavi Pant, head of global health at the Health Effects Institute, said, "Data on air pollution levels and the associated health and economic impacts point to the need for long-term, sustained air quality management in Bangladesh and across South Asia. These data also point to the fact that it is crucial to plan multi-pollutant mitigation strategies and not focus on individual pollutants such as PM2.5. Also, since the sources are similar across the region, cooperation on both scientific research and policy action can spur faster action."