India, Nov. 11 -- London woke up to more than just another foggy November morning this week. As thick fog settled over the capital and weak winds failed to clear the air, pollution built up near the ground, pushing fine-particle levels into the "very high" category across parts of England.

The situation prompted Mayor Sadiq Khan to issue a high air pollution alert for London on Tuesday, November 10, urging residents, especially vulnerable people, to limit their exposure. At the same time, the Met Office warned that dense fog could slow road, rail and air travel, creating a double threat for commuters.

The pollution spike followed a weekend of Bonfire Night celebrations, fireworks and Diwali events. Officials said smoke from those activi...