[14]

That would make sense but I would also wager that the wind blowing over the water acts as a bit of a filter. As wind contacts the water, some of the pollutants would be absorbed by the ocean and taken out of the air cleaning it. Just a theory.

[Dumblydorr]

I don't think that's a major factor, the wind is mostly high above the water. Being far from polluting sources is the key for Ireland. Specifically, their western coast gets fresh air from thousands of miles of ocean, though admittedly there's a little bit of shipping and boating there. Compare to here on East Coast US, the wind comes from the continent, any fire out west/northwest leads to smog and haze here.