Not the only emissions too. Faecal emissions (sorry if you're having your lunch) are locally polluting and unhygenic. It's not often recorded the mass rejoicing when cars replaced horses in cities. No longer having to step over/round piles of sh*t was a major improvement in everyone's life.
I remember some years ago waiting on my bike at some traffic lights behind a pair of police horses, which then proceeded to decorate the road in front of me with their emissions. No apologies from the officers, no attempt to clean it up. Disgusting stuff.
Apparently it doesn't count at littering.