Mumbai, Jan. 24 -- The Air Quality Index (AQI) in the city rose to 104 - according to the Central Pollution Control Board (CPCB) - on Thursday, indicating the air was unhealthy for sensitive groups, after hovering at 80-90 for several days. A thick layer of smog engulfed large parts of the city till the afternoon, and doctors reported a surge in complaints about respiratory illness. Data from CPCB showed multiple pollution hotspots across the city, while many air quality monitoring stations were non-functional for several hours, leading to gross underreporting of AQI levels. Experts cautioned that air quality in the city was prone to sharp localised fluctuations. A senior official from the Brihanmumbai Municipal Corporation (BMC) told Hindustan Times that all flying squads had been instructed to increase monitoring and issue stop-work notices to construction projects that flouted norms. "We are also issuing notices to AQI monitoring station operators for non-functional monitors," he said, reuesting not to be identified. As reported by Hindustan Times on Wednesday, the BMC has already issued stop-work notices to 106 construction sites across Mumbai for failing to install mandatory air-quality-monitoring systems. Gufran Beig, chair professor at the National Institute of Advanced Studies (NIAS) and founder and project director of System of Air Quality Forecasting and Research (SAFAR), said the latest spike in pollution was driven by atmospheric conditions rather than wind patterns. "North India has just come out of its peak pollution phase and there is a lot of moisture in the air. When moisture increases, the air becomes heavier and its holding capacity for pollutants increases," he explained. Mumbai's weather variability made such fluctuations common, he said. "Like temperature, AQI keeps varying. On days when humidity is very high, smog formation is more frequent." Doctors said the deterioration in air quality in the city was evident in the surge in patients with respiratory ailments. Pulmonologist Dr Lancelot Pinto said the trend had been unfolding over the last few months, especially since November, when people who returned to Mumbai after travelling elsewhere started complaining about respiratory issues. "The situation has been pretty bad. Several irritants in the air have led to asthma cases surging, and we have had to put patients on steroids," he said. Dr Gautam Bhansali, consultant physician at Bombay hospital, said cases of sore throat and cough have gone up again after a brief lull last week. "Some patients had to be admitted due to severe throat problems, and investigations revealed that irritation in the lungs was the cause," he said....