Mumbai experienced a significant deterioration in air quality on Sunday, January 4, with the overall Air Quality Index (AQI) reaching levels categorized as 'moderate' to 'severe' across various monitoring stations. While some reports indicated an AQI as high as 356 in the 'severe' category, others placed it at 140-144 in the 'moderate' range. Areas like Byculla, Mazgaon, and Malad reported particularly high pollution levels. Meteorologists attribute the haze and pollutant trapping to reduced wind speeds, with partly cloudy skies and haze expected to persist.