I wasn't doing much spraying to be honest, but we usually waited for relatively windless days to spray (not for health reasons, but usually because we didn't want to roundup the neighbors' crops/lawns/etc).

Oh that's true, I know that and I'm not sure why I didn't think of it. Herbicide drift is a nightmare scenario of horticulturalists. In certain circles people plan out earth berms and wind breaks of sacrificial plants so their flowers and vegetables don't get hit. Most of us aren't brave enough to build something on the edge of farmland, let alone in the middle of it. But there's always some masochist who will try. 'We' don't have a very high opinion of farmers spraying on a windy day.

Similarly flatlander recreational/club bicyclists don't have anything nice to say about farmers spraying anhydrous ammonia on a windy day. Luckily didn't happen very often, and never up close (>400 yards), but that's still enough to really get your attention.