PORTLAND, Ore. (KOIN) – When the 4th of July comes around, we know that there are going to be a lot of celebratory fireworks. From massive firework shows to just lighting off the fireworks that you find enjoyable from your own safe space. With those loud and vibrant explosions comes smoke. You may notice after a firework show that the smoke hangs around for some time. It may even linger in the night sky for hours. What is going on for this to take place?

During the day the sun will heat the surface leading to the air above to rise because it is less dense. That rising air becomes turbulent and allows for the air to disperse. That means it is generally more windy than at night because of the heat. These steps allow for smoke to disperse more so than at night. Well, since fireworks tend to be set at night when it is dark, conditions aren’t favorable for smoke dispersion. This is because of the cool night hours where we lose heat out to the atmosphere leading dense air near the surface. Unless there is a disturbance, the wind at night is mostly calm. That means the smoke is mostly caught near the surface with nothing to help mix it out. In some circumstances, a strong inversion where warm air aloft traps the smoke near the surface can lead to very poor air quality and restricted visibility.

Air quality took a hit 4th of July night around Portland and surrounding neighborhoods because of the smoke from fireworks. The wind will still be calm Sunday morning and you may notice a smoky haze Sunday morning.