Possible Clues:

• Difficulty with breathing has two characters passing out by motorway - it's the pollution
• Stink receding during the morning's end
• Pollution in the atmosphere
• Unwholesome atmosphere or unhealthy vapours
• Hum fast track like master
• A script to end the wrong way, creating unpleasant atmosphere
• Unpleasant, polluted, air
• Like Mother, I am back with pollution
• Air around a fen
• Foul vapours or unwholesome air