Read the text. Choose the best word that fits the space.

One of the most pressing issues is air pollution. Russia’s industrial hubs, such as cities like Moscow, St Petersburg, and Norilsk, face severe air quality problems due to 2. ______ from factories, power plants, and vehicles. Norilsk, for instance, is home to one of the world’s largest nickel and palladium mining operations, and it has become notorious for its toxic pollution, where the air often contains harmful levels of sulfur dioxide. This type of air pollution has caused widespread environmental damage, including the death of entire forests around the industrial areas.

• pollution
• gasses
• emissions
• garbage