Despite the heavy pollution blanketing Beijing, runners did not let it stop them from participating in the maskless Beijing Marathon on Sunday. Many even braved the warm temperatures, with some opting to wear shorts, making it one of the hottest Octobers on record.

Although there was a hazy brown fog present, approximately 30,000 runners began their marathon at 7:30 a.m. (2330 GMT) from Tiananmen Square. The course covered 42.195 km (26.2 miles) through four districts of Beijing.

On Sunday, IQAir, a Swiss company that measures air quality, reported that Beijing was the second most polluted major city in the world.

According to a witness from Reuters, even though the sky appeared gloomy in the Haidian district outside of Beijing, people still came to Fragrant Hills Park to admire the autumn leaves.

On Sunday morning, China’s national forecaster recommended that people wear masks due to moderate to severe levels of air pollution.

The National Meteorological Center reported on Sunday that China will experience smog and fog in certain regions for the next few days. This will result in decreased visibility and may impact travel in northeastern, northern, central, and some eastern provinces.

The observatory in Beijing warned that visibility across the city will decrease to less than 1 km (0.62 miles) overnight.

The forecaster stated that the hazy conditions are predicted to gradually diminish and disappear by Friday. However, there is a possibility of thick fog in certain areas of Jiangsu, Anhui, and Sichuan provinces for the next three days, which could result in visibility being reduced to less than 200 meters (650 feet).

Emergency measures were implemented on Friday in Tangshan, Handan, and other cities in the northern province of Hebei in response to anticipated high levels of air pollution. The notices did not specify a timeframe for when the restrictions would be lifted.

Experts have stated that the current October weather, which is warmer than usual, is a result of smog and weaker cold air currents from the north. This is due to the polar vortex, which usually sends cold air southward, being located further north in recent times.

According to the national weather bureau, Beijing’s temperature reached a high of 19 C (66 F) on Sunday.

Some regions in China, particularly in the north and northeast, have been facing temperatures that are 2 to 4 degrees Celsius (4-7 Fahrenheit) above average over the past 10 days.

Fang Chong, the chief forecaster of the meteorological bureau, stated that currently, 237 national meteorological stations have experienced record-breaking high temperatures in late October. This is a relatively uncommon occurrence, according to state media reports.

Mild chilly air flows were predicted to continue for the remainder of the month before gradually cooling down in early November.

Although originally predicted to dissipate within a week, the smog persisted with a hazy atmosphere reminiscent of Beijing’s annual race from ten years ago. In 2014, late Premier Li Keqiang declared a “war” on pollution, and numerous marathon participants wore masks for safety.