Often, I get nearly knocked out from inhaling sewage gases oozing through manholes in big cities. They are so bad . I just thought about installing big fans to suck air through the manholes to keep the sewage gases moving in the right directions that is toward the treatment plants where they belong! This can also help suck in heavy traffic smog to help reduce air pollution on the busy streets. The fans can be solar powered . I think it is well worth the expenditure in all big cities to enhance the big city experience. We can do the same for the neighborhoods as you know that there is ventilation pipes dotting on all rooftops for the sewage gases to escape. I think this is so medieval already.. We can improve the air quality even further with installations of fans in strategic locations in the main sewage pipes to draw air in the right directions back toward the sewage plants.