MUMBAI, Dec. 18 -- In an effort to improve the city's air quality (AQI), the BMC, over the last 16 days, has issued stop-work notices to 121 construction sites, both government and private, and show-cause notices to another 353 sites for not following pollution norms. This action, said the civic body, had led to a significant improvement during the first half of December compared to the same period last year-where the AQI was 167-158 in December 1-16 last year, this year it stands at 105-113. Deputy municipal commissioner (Environment and Climate Change) Avinash Kate, while confirming this, said that the BMC also used misting machines at 253 locations and undertook road cleaning with water on 376 locations. Additional municipal commissioner (eastern suburbs) Dr Avinash Dhakane too attributed the improvement to these continuous and multi-pronged efforts. Kate stated that the BMC's efforts had borne fruit as testified by the fact that pollution levels in the last 45 days have rarely been triggered by PM 2.5 levels, attributed mainly due to vehicular and industrial emissions. "The BMC is already doing its bit by bringing in 712 electrical BEST buses, along with 50 double-deckers, as part of the Rs 900-crore project to electrify its entire fleet," he said. "Besides, efforts to electrify 295 wooden bakeries, of which about 63% have already converted, have also helped." Mumbai's air quality had deteriorated sharply from around November 11, with several monitoring stations slipping into the 'Poor' category and PM 2.5 levels remaining dangerously high. During this peak, Chakala at Andheri East recorded an AQI of 255, Mazgaon touched 252, while Powai logged an AQI of 221, with PM 2.5 levels surging to 338. Multiple locations reported PM2.5 concentrations above 300 for long stretches. In response, the authorities imposed GRAP-IV, the strictest level under the Graded Response Action Plan. The measures included a complete halt on construction activity, restrictions on diesel generator use, curbs on non-essential commercial activities and tighter enforcement of vehicular emissions. Following this, the AQI improved significantly, ranging at around 120 till the evening of December 17. Overall AQI on Wednesday stood at 137 (moderate). Station-wise readings showed Bandra-Kurla Complex and Mindspace, Malad West, at 167, Siddharth Nagar, Worli, at 168, Ghatkopar at 148, and Navy Nagar, Colaba, at 141. Officials said that continued monitoring was in place, while warning that any drop in wind speed could push pollution levels upward again....