湿热的午后暑气使他筋疲力尽。

The oppressive afternoon heat had tired him out.

据《月令七十二候集解》说：“处，去也，暑气至此而止矣。”

According to "make seventy-two month waiting Variorum, " said: "The Office, and go, heat to this full length carry on.

“处”，止也，暑气至此而止。 处暑过后，我国大部分地区将告别夏日，进入秋季。

End of Heat implies that most parts in China are getting rid of the hot summer and entering autumn.