Mumbai’s air quality index worsened on Wednesday to levels that the city had not seen since Diwali in October 2017, the Hindustan Times reported. Haze engulfed the city since morning, and temperatures rose significantly.

Monitoring stations across the city recorded poor to moderate air quality, an official of the India Meteorological Department told PTI, attributing it to suspended dust particles in the air, heavy traffic and construction work.

On Wednesday, Mumbai had an air quality index of 273, according to SAFAR (System of Air Quality Forecasting And Research) – this was higher than Tuesday’s 268. An index level between 201 and 300 is categorised as “poor”. Researchers at the organisation said the air quality index would improve slightly from Thursday, to around 265. At 4.52 pm on Wednesday, the concentration of the pollutant PM 2.5 – particulate matter of size up to 2.5 microns – was 327 micrograms per cubic metre (very poor) in Bhandup and Bandra.

“We expect pollution levels to continue in the ‘poor’ category till Thursday as western disturbances are pulling in a lot of moisture, which allows pollutants to be suspended close to the earth’s surface,” Gufran Beig, project director at SAFAR, told the Hindustan Times. “If there’s more sunshine, the heat will reduce the moisture and pollution levels.”

Higher moisture levels also led to the rise in temperatures. Santacruz recorded 21.5 degrees Celsius, 4.3 degrees above normal, and Colaba recorded 23 degrees Celsius, 3.6 degrees above normal, the Hindustan Times reported.