As the seasons change people often wonder when they should clean their windows. Is it a once a year event? Or do you clean them every turn of the season? Different seasons bring different window debris. So you should in general clean your windows at a minimum once a season to get the most benefit out of them.
Fall
- rain
- mildew
- mold
- dirt
Winter
Winter is a jolly time.
- salt
- dirt
- soot (coal)
- sulfates
- nitrates
"...with snow and rain when it falls from the clouds, its actually picking up pollution from the atmosphere. So you get things like carbon from fires, dirt, dust, salt..."
source: https://www.npr.org/sections/thesalt/2016/01/23/463959512/so-you-want-to-eat-snow-is-it-safe-we-asked-scientists
source: Meteorologist Says Licking Icicles Is Like ‘Eating Poop’ https://www.youtube.com/watch?v=alM0jhS9V3A
Spring