Horse manure emits methane, ammonia and hydrogen sulfide. Dried up it also becomes brittle and susceptible to turning into PM emissions if disturbed. It was wa

Horse manure emits methane, ammonia and hydrogen sulfide. Dried up it also becomes brittle and susceptible to turning into PM emissions if disturbed. It was way more of a problem than just aesthetics and cars, even in their early days, appeared cleaner overall. The one thing we never got back are noise levels - modern cities are loud.