Chandigarh, Dec. 21 -- Chandigarh faced a worsening spell of air pollution and winter chill on Saturday, with the Air Quality Index (AQI) soaring to 302 - the highest since Diwali on October 21 - even as dense fog continued for the fourth consecutive day. The foggy conditions also dragged the day temperature down to 18.3degC, 2.3 degrees below normal and the coldest recorded so far this season. While current conditions are expected to persist over the weekend, the fog spell is likely to intensify further from December 24 onwards, potentially leading to colder conditions. As per the daily bulletin released by the Central Pollution Control Board (CPCB), Chandigarh's AQI climbed sharply from 254 to 302 over the past 24 hours, entering the "very poor" category for the first time since Diwali, two months ago. The AQI of Panchkula also rose steeply, from 145 to 361, placing it in the "very poor" bracket as well. An AQI between 301 and 400 is considered very poor and can cause respiratory illness on prolonged exposure. Out of the 242 cities included in the CPCB data, Panchkula ranked as the sixth most polluted, while Chandigarh stood 16th. Station-wise, the Continuous Ambient Air Quality Monitoring Station (CAAQMS) in Sector 25 recorded the highest pollution levels. At 8 pm on Saturday, the AQI here stood at 313, while it was 292 each at the CAAQMS stations in Sector 22 and Sector 53, which fall in the "poor" category. Foggy weather leads to temperature inversion, causing pollutants to remain trapped near the surface and AQI levels to rise significantly. According to the India Meteorological Department (IMD), visibility was as low as 200 metres at 5.30 am and 8.30 am, which is classified as "dense fog". Even later in the day, visibility did not improve beyond 1,500 metres, categorised as haze. Because of the persistent fog cover, the maximum temperature fell from 19degC on Friday to 18.3degC on Saturday. Chandigarh was colder than Dharamshala, which recorded 19degC, and Solan at 24.5degC, though Shimla was colder at 17degC and Manali at 15.6degC. IMD Chandigarh director Surender Paul said the fog spell would continue as a Western Disturbance was currently affecting parts of Jammu and Kashmir. He added that while fog cover was likely to reduce slightly for a day or two, it was expected to intensify again from December 24 onwards due to moisture-laden winds brought by a fresh Western Disturbance. The foggy conditions, however, led to a rise in minimum temperature from 7.9degC on Friday to 11.3degC on Saturday, which was 3.6 degrees above normal. IMD officials explained that fog at night prevents the earth's heat from dissipating, resulting in above-normal night temperatures. If dense fog persists during the day, a further drop in maximum temperature could lead to "cold day" conditions in the city. Cold day conditions are declared by the IMD in this region when the minimum temperature drops below 10degC and the maximum temperature remains 4.5 to 6.4 degrees below normal. Last year, rain spells in the second half of December had triggered cold day conditions around this time. This year, however, the city has not recorded any rainfall in December so far....