RE: does moisture of atmosphere (humidity) affects size of tomato?
No, I wouldn't think so. Humidity has a number of effects on tomato plants , most of them negative. Humid conditions favor fungal diseases that tomatoes are prone to. Humid conditions inside greenhouses, with not enough air movement also make pollination more difficult:
In addition, learn to use intermittent ventilation on
cool days to reduce moisture condensation inside the
house. The drier the foliage can be kept and the
more air movement in the greenhouse, the more
favorable the conditions for pollination.
Growers who have previously had low ventilation
capability have doubled their yields
tomatoes in several situations when they replaced
old houses and increased their ventilation capability.
https://extension.tennessee.edu/publica ... pb1609.pdf
Doubling the yield here was from improved pollination leading to more tomato fruits set. It was not about the size of the tomatoes.
I expect more important than humidity is hours of direct sun:
Grow tomatoes in the sunniest, warmest part of your garden. Cherry tomatoes can get by on 5-6 hours of sun and still produce fruit, but larger tomatoes need 8-12 hours of sun a day for best performance. https://www.grow-it-organically.com/grow ... CqN3M.dpuf