This is the 3889th most frequent French word.
améliorée
"Improved."
In this sentence, 'améliorée' is used as a past participle in the passive voice, indicating that the air quality ('la qualité de l'air') was improved as a result of an action.
La qualité de l'air a été améliorée grâce aux filtres installés.
The air quality has been improved thanks to the installed filters.
Here, 'améliorée' describes a noun ('méthode') and is used as an adjective indicating that the described method is better than a previous one through improvement.
Nous avons adopté une méthode améliorée pour le tri des déchets.
We have adopted an improved method for waste sorting.
In this usage, 'améliorée' is part of a passive voice construction ('peut être... améliorée'), showing that productivity could be enhanced through appropriate means.