Smoke and haze will linger across New Delhi long after the lanterns and fireworks from this year's Diwali have burned out.
SAFAR, India's air quality information service, has warned that New Delhi is going to be "critically polluted" during the festival on Nov. 11 and in the days following.
The organization's health advisory encouraged people to avoid all outdoor physical activity.
It also recommended that those with heart or lung disease, older adults and children remain indoors, keeping activity levels low through Nov. 12.
Diwali, nicknamed the Festival of Lights, is one of the most celebrated festivals in India. Taking place 18 days after Dusshera, it is an ancient celebration signifying the Hindu New Year.
During the celebration, it is customary to burn lamps and candles and light fireworks, activities that exacerbate India's poor air quality issues.
"There is enough moisture in the air and atmospheric holding capacity is quite high for particles emitting from firecrackers," Gufran Beig of SAFAR told TIME.
Nov. 12-13, pollutant levels in New Dehli are expected to rise by more than 150 percent, they reported.
Already, New Delhi is recognized by the World Health Organization as one of the world's worst polluted cities.
"The problem is this stagnant weather pattern over the northern India," AccuWeather Meteorologist Eric Leister said.
"The smoke and pollution from the fireworks will linger in the atmosphere for several days. No rain and light winds will cause only slow dispersion of the pollution," he said.
High concentrations of pollutants will be less of a problem farther south, where a tropical low will produce scattered showers and thunderstorms across Tamil Nadu, Kerala, southern Andhra Pradesh and southern Karnataka.