New Delhi's air quality has already reached its worst level this year. And the Hindu festival of lights, Diwali, which starts this weekend, is likely to make things even worse as the traditional rounds of firecrackers add to the air pollution.

During the five-day festival, revelers set off smoke bombs, sparklers and aerial fireworks that spew clouds of noxious gas.

"It's a very critical, dangerous week ahead of us," said Delhi-based environmental activist Vimlendu Jha.

The Diwali fallout is an issue every year – but especially during a pandemic. Research illustrates that polluted air is not only bad in general, it's bad for the transmission and severity of COVID-19.

Delhi's annual end-of-year downturn in air quality is due to a mix of exhaust from coal-fired power plants and vehicles, dust from construction sites and smoke from farmers burning crop waste. The pollutants linger in the air because the summer winds drop off. One 2018 study concluded that Diwali leads to a "small but statistically significant increase" in air pollution in India's capital.

Addressing concerns about the impact of pollution on COVID-19 cases, Arvind Kejriwal, Delhi's chief minister, said earlier this month: "The sky is filled with smoke and because of this the coronavirus situation is worsening."

He did not offer proof. However, studies, including one from Harvard University, have shown that long-term exposure to air pollution not only makes you more vulnerable to COVID-19 but can also lead to worse outcomes.

Another study published in the European journal Cardiovascular Research estimates that 15% of COVID-19 deaths worldwide can be attributed to air pollution.

"If both long-term exposure to air pollution and infection with the COVID-19 virus come together then we have an additive adverse effect on health, particularly with respect to the heart and blood vessels, which leads to greater vulnerability and less resilience to COVID-19," Thomas Münzel, one of the authors of the European study, said in a press release.

"It's a double jeopardy on your lungs," Dr. Pratibha Gogia, a respiratory specialist in Delhi, told NPR.

India has more than 8.5 million total reported cases, second behind the United States. While new cases in most parts of the country have been on a downward trend in recent weeks, Delhi has been experiencing its deadliest spike in infections.

Gogia said even without COVID-19, critical care beds at her hospital fill up every winter due to an increase in pollution-related respiratory ailments.

"So this year the crisis will deepen because half of our intensive care units are filled with corona and the rest will not be sufficient for routine respiratory problems," Gogia said.

Like previous years, the government has banned Diwali firecrackers this year, but it's rarely enforced, said Jha, the environmental activist.

The government has started a campaign urging drivers to turn off their engines at traffic lights to cut vehicular fumes. Trucks fitted with anti-smog guns are circulating in Delhi, spraying mist to try to clean the air.

But these are all "Band-Aid solutions," Jha said. The government should focus instead on addressing the root of the problem, he said. That could include measures such as reducing the number of private vehicles on the road by boosting green public transport, reducing construction activities that spew dust in the air and stopping people from burning garbage in the open, he said.

"Urgent political action, good governance on the ground, transaction of existing laws — these are the things that the government will need to do urgently," Jha said.

Sherry Frosh belongs to a mom's group that fights pollution. She said there is one hopeful thing that's come out of the pandemic. More Delhiites are wearing masks because of COVID-19, and that might end up protecting them from the pollution, too.

And for a few precious months this spring, when India went under a strict coronavirus lockdown, emptying roads and shutting factories, Delhi residents got a taste of what their skies could look like: deep, clear blue.

"People were talking about seeing mountains in the distance and great visibility all around. They got used to [being outside and hearing] birds singing and smelling flowers and breathing in," Frosh said.

And so this winter, instead of resigning themselves to the pollution, Frosh said she hopes the pandemic makes Delhiites realize their air quality is an urgent health crisis, too.

Copyright 2021 NPR. To see more, visit https://www.npr.org.