Mumbai's BKC records 425 AQI, civic officials say monitoring system malfunctioned. Mumbai's air quality has deteriorated after monsoon's withdrawal, with Bandra Kurla Complex recording AQI of 425 in 'Severe' category on Sunday. Civic officials attributed the spike to a possible malfunction in the monitoring system and asked IITM to replace it. However, experts cited altered weather patterns and reduced rainfall amid El Niño conditions as factors contributing to unhealthy air.