Photos: Fog and smog engulf New Delhi

Residents of the Indian capital New Delhi and its suburbs have been waking up in recent weeks to cloudy mornings with skies turning gray due to air pollution.

A thick blanket of smog engulfs the capital in winter as cold, dense air traps construction dust, vehicle exhaust and smoke from burning crop stubble in neighboring states to the north, causing a rise of respiratory diseases among the 20 million inhabitants of the city.

The air quality index at almost all monitoring stations in New Delhi was between 300 and 400 or in the “very bad” category on Monday, which experts say leads to respiratory illnesses if there is prolonged exposure. However, it was an improvement over last week’s reading of 400-500, which is described as “serious”.

Indian authorities on Friday closed factories and construction sites, restricted diesel vehicles and deployed water sprinklers and anti-smog guns to control haze and smog engulfing the capital region’s skyline.

The Delhi government closed primary schools and restricted outdoor activity for older students as the air quality index exceeded 470, more than 10 times the global safety threshold, according to the Central Control Board of the Pollution, managed by the state. Elementary schools will reopen on Wednesday.

Delhi State Environment Minister Gopal Rai said private demolition and construction will continue to be banned, but public works related to roads and power transmission will be allowed.

Almost every year, New Delhi tops the list of the many Indian cities that are breathless after the Diwali festival celebrations with their huge fireworks. The crisis is particularly exacerbated in the winter when the burning of crop residues in neighboring states coincides with lower temperatures that trap the deadly smoke, which travels to New Delhi and causes increased pollution.

Air quality could worsen later this week, the Weather and Air Quality Forecasting and Research System (SAFAR) said on its website.