I appreciate the focus of the article and the explanations laid out for us. I would like to point out though that the two photos used as the "Less Polluted" and

I appreciate the focus of the article and the explanations laid out for us. I would like to point out though that the two photos used as the "Less Polluted" and "More Polluted" examples may not fit the descriptions. Less Polluted shows a point in a city after a rain shower. The passage of a storm front tends to leave the air behind it more clean that it was before it arrived. That example makes the most sense. More Polluted does not make sense when you look at the photo since it obviously shows a storm front making it's way across a city, maybe the same one in the "Less Polluted" example. That storm is cleaning the air as it passes and the buildings in the foreground look like the storm has already passed. To me that means that the air from the photographer's vantage point should be clean already. It isn't possible to know whether you are looking east at dawn or west at sunset but either way that storm has passed, bringing clearer air to the city. A better example would be a photo of that same city on a cloudless summer day when the air is choked with smog and those who care are wishing for a nice storm like the one pictured to sweep through and clean it all up.