I find it's the cold air in the mornings that I'm breathing large lungfulls of that has the biggest effect. I thought about using my asthma puffer this morning but don't really want to unless it's particularly bad. It's lovely weather when you don't need to breathe hard.
I definitely notice the same thing when it's really cold. I didn't think it was that chilly this morning. I did have a joyous sprint over an empty London Bridge in the sun this morning. Perhaps it was those lung-fulls that did it.
Fair point. Still t-shirt weather though.