There’s no true substitute for clean air, so the biggest improvement comes from timing: shoot when pollution is least noticeable, such as early morning, on colder days, or just after rain.

To reduce the effect when you must shoot anyway:

• Use a polarizer in the right conditions. It can help with haze, especially when shooting about 60–120° from the sun; it’s less useful on overcast days.
• Avoid backlighting, which illuminates airborne particles and makes haze more obvious.
• Increase contrast or adjust the tone curve, either in-camera for JPEGs or later in RAW processing, to restore some punch.

You can also lean into the atmosphere instead of trying to remove it. Smog can become part of the story, especially for documentary or environmental images. Night scenes with colored city lights can also work well, since the haze can create a distinctive glow rather than just making daylight scenes look flat.

In short: optimize timing first, use a polarizer selectively, avoid lighting that emphasizes particles, and use contrast adjustments in post to recover some clarity.