NEW DELHI/LAHORE, Nov 3 (Reuters) - Air quality deteriorated sharply in parts of northern India and adjoining Pakistan on Tuesday, with the onset of pre-winter smog making Lahore the world's most polluted city and authorities in Delhi imposing curbs to fight the toxic haze over the capital.
Air pollution becomes a severe problem for the region around this time of the year when cold, dense air traps emissions from vehicles, construction sites and crop waste burning, pushing pollution levels to the highest in the world and exposing residents to serious respiratory risks.
Fireworks during the Hindu festival of Diwali, which falls on November 8 this year, worsen the pollution in India.
Early on Tuesday, the air quality index (AQI) in Lahore stood at 447, according to IQAir, a Swiss group that measures air quality levels based on the concentration of toxins. An AQI reading of up to 50 is considered good with little or no health risk.
Lahore's PM2.5 concentration was 60 times higher than the World Health Organization's annual PM2.5 exposure guideline. PM2.5 refers to particulate matter measuring 2.5 microns or less in diameter that can be carried into the lungs, risking deadly diseases and heart problems.
A significant drop in temperatures and sluggish winds have affected air quality in Lahore, authorities said.
Pakistan's government has intensified action against brick kilns violating environmental regulations and continues to urge farmers not to burn crop residue after harvesting.
The AQI in Delhi was lower at 215, as per IQAir. India's Central Pollution Control Board rated the capital city's air quality "very poor" with a higher AQI reading of 332.
The Swiss and Indian readings vary due to the different AQI scales and methodologies used to calculate and classify air pollution levels.
Delhi's graded pollution control measures — including restrictions on polluting vehicles, construction activities, the use of coal and firewood in eateries, and boosting public transport services — took effect on Monday.
With Diwali over the weekend expected to add to the pollution, India's Supreme Court has allowed only low-polluting fireworks to be burst for three hours each on Saturday and Sunday.
(Reporting by Ariba Shahid in Islamabad, Mubasher Bukhari in Lahore, writing by Tanvi Mehta; Editing by YP Rajesh and Xevi Fontdegloria)
