MUMBAI, Oct. 25 -- Post-monsoon showers this year are keeping air pollution in check, curbing the usual spike during Diwali, when firecrackers release a surge of particulate matter and smoke into the air. Slightly more frequent than usual, the showers are a timely blessing. After light showers in Mumbai, Kalyan and Thane on Friday evening, the Air Quality Index (AQI) registered 75 (satisfactory), three days after it peaked at 211 (poor) on October 21. In just one hour, between 8pm and 9pm, Byculla and Wadala logged 64mm and 62mm of rainfall, respectively. Grant Road recorded 55mm and Sewri 54mm, according to data from the BMC. The western and eastern suburbs experienced only a light drizzle. "This year, post-monsoon showers are more frequent than in the last couple of years, due to western disturbances. This also indicates that the winter will be severe," said Gufran Beig, chair professor at the National Institute for Advanced Studies, Bengaluru. "But these showers will soon subside." According to IMD, post-monsoon showers will continue over the weekend in Mumbai. The IMD has issued a yellow alert for the city, with the possibility of moderate rain, thunderstorms and gusty winds. Air quality, meanwhile, has recorded a predictable trend. As if on cue, AQI rose on October 10, as soon as the IMD announced the withdrawal of the monsoon. It logged 134 or "moderate" on that day. AQI remained in the moderate range (101 to 200) and fell to 88 (satisfactory) on October 17, due to the first post-monsoon showers. AQI rose again, from October 18 to 20, hovering in the "moderate" range, before it suddenly peaked on October 21, a "poor' AQI of 211, coinciding with the Diwali festivities. On October 22 and 23, the AQI returned to "moderate", recording 110 and 108, respectively. Friday brought a breath of fresh air, with post-monsoon showers lowering AQI to 75 (satisfactory). A further analysis of air quality from October 13 to 22 showed that a majority of the 30 ambient air quality systems recorded particulate matter (PM) 10 levels beyond the permissible 100 micrograms per cubic meters mark, for a 24-hour average. On seven days, more than 20 stations breached the mark, while on three days, around 15 stations breached the mark. On October 20, 28 stations crossed the limit, according to a report from the Centre for Research on Energy and Clean air (CREA). "It is crucial for the authorities to address not just seasonal pollution spikes but also everyday sources such as construction dust, traffic emissions, and other contributors that are steadily degrading air quality," said Manoj Kumar, analyst at CREA....