This is the 4686th most frequent German word.
verschlechterte
"Worsened" or "deteriorated."
Here, 'verschlechterte' functions as the past-tense form of the verb 'verschlechtern', indicating that the air quality has deteriorated.
Die Qualität der Luft verschlechterte sich durch die Bauarbeiten.
The quality of the air worsened due to the construction work.
In this sentence, 'verschlechterte' again acts as the past-tense verb form, describing the decline in the economic situation.
Die Wirtschaftslage in dem Land verschlechterte sich nach der Krise.
The economic situation in the country worsened after the crisis.
Here, 'verschlechterten' is a past-tense plural form, describing a negative change in conditions due to external factors.