Possible Clues:

• Exists on oxygen at pub ¿ that¿s the pressure living in this climate
• One fly straddles black line on weather map
• Lives on old bank, on which pressure is constant
• Line on map is for Oscar going to pub
• Line for plotting atmospheric pressure
• A Boris (anag.)
• I'm high-flying Brit in meteorological line
• Boris takes a strangely pressurised line
• Weather map air pressure line
• Met map pressure line