The report has also said Bihar's Begusarai emerged as the world's most polluted metropolitan area.

The news agency PTI quoting the report said with an average annual PM2.5 concentration of 54.4 micrograms per cubic metre, India had the third worst air quality out of 134 countries in 2023 after Bangladesh (79.9 micrograms per cubic metre) and Pakistan (73.7 micrograms per cubic metre).

It also said in 2022, India was ranked as the eighth most polluted country with an average PM2.5 concentration of 53.3 micrograms per cubic metre.

Begusarai stood out as the most polluted metropolitan area globally with an average PM2.5 concentration of 118.9 micrograms per cubic metre, it said.

It added the city did not even figure in the 2022 rankings.

Delhi's PM2.5 levels worsened from 89.1 micrograms per cubic metre in 2022 to 92.7 micrograms per cubic metre in 2023, it mentioned.

Delhi was ranked the most polluted capital city in the world four times on the trot starting 2018.

It is estimated that 1.36 billion people in India experience PM2.5 concentrations exceeding the World Health Organisation (WHO) recommended annual guideline level of 5 micrograms per cubic metre, the report said.

Also, 1.33 billion people, 96 per cent of the Indian population, experience PM2.5 levels more than seven times the WHO annual PM2.5 guideline, it said.

The report stated this trend is reflected in city-level data, with more than 66 per cent of the country's cities reporting annual averages greater than 35 micrograms per cubic metre.

IQAir said the data utilised to create this report was aggregated from the global distribution of more than 30,000 regulatory air quality monitoring stations and low-cost air quality sensors operated by research institutions, governmental bodies, universities and educational facilities, non-profit non-governmental organisations, private companies and citizen scientists, it said.

The 2022 World Air Quality Report included data from 7,323 locations in 131 countries, regions and territories. In 2023, those numbers have grown to include 7,812 locations in 134 countries, regions and territories, it mentioned.

Causing an estimated one in every nine deaths worldwide, air pollution is the greatest environmental threat to human health, it said.

According to the WHO, air pollution is responsible for an estimated seven million premature deaths worldwide every year.

Exposure to PM2.5 air pollution leads to and exacerbates numerous health conditions, including but not limited to asthma, cancer, stroke and lung disease, it said.

Exposure to elevated levels of fine particles can impair cognitive development in children, lead to mental health issues, and complicate existing illnesses, including diabetes, it added.