A drop in city night temperature, which was 4 degrees Celsius below normal on Friday morning, increased pollution levels in Mumbai.

While the pollutant measuring indicator – air quality index (AQI) — recorded ‘moderate’ pollution on Wednesday and Thursday, the AQI shot up to 204, falling under the ‘poor’ category on Friday. A similar AQI of 205 was predicted by the System of Air Quality Weather Forecasting and Research (SAFAR) for Saturday. AQI levels between 201-300 falls under the ‘poor’ category and 301-400 under ‘very poor’, indicating a health risk for people sensitive to air pollution.

Researchers from SAFAR said the drop in night temperatures from 20 to 18 degrees Celsius allowed pollutant particles to settle closer to the city’s surface. “Due to inversion, wherein pollutants do not get dispersed easily due to cold temperatures, air quality was poor in Mumbai. A drop in wind speed and low moisture levels allows pollutants to be further trapped,” said Neha S Parkhi, senior programme manager, SAFAR.

Meanwhile, the Santacruz weather station, representative of Mumbai, recorded the night temperature at 18.2 degrees Celsius, which equalled the lowest minimum temperature for November in 2014. The lowest minimum temperature for the month was recorded at 14.4 degrees Celsius in 2007. The Colaba weather station, however, recorded 23 degrees Celsius, which was a degree Celsius below normal.

Officials from the weather bureau said low minimum temperatures are likely to continue over the weekend. “Winds over the city are carrying cool air from the north and are mostly north-easterly to northernly. The phenomenon is common during this time of the year and we expect it to die down by next week,” said VK Rajeev, director, western region, India Meteorological Department (IMD).

On Friday, the air quality station at Nerul, Navi Mumbai recorded highest pollution level with an AQI of 309, falling under the ‘very poor’ category followed by Malad (260) and Andheri (245) both recording ‘poor’ AQI levels.

Maximum temperatures at both the suburbs and south Mumbai were a degree Celsius below normal. The city also observed a dip in moisture levels as Santacruz recorded 51% humidity while 77% was recorded at Colaba.

A clear sky was predicted for Saturday with temperatures similar to that of Friday.