That might be my favorite app. Pro Tier 1 is well worth the money if you don't already have it. Tier 2 has a ton of cool features but it's $100/year.. too much for my needs.
Haven't those been mandatory since the mid-70s? They certainly made a big difference, but I think the improvements we've seen in the past 20+ years have much more to do with the 1990 amendments to the Clean Air Act than anything else. Those regulations targeted the big commercial and industrial pollution emitters.
I'm only in my late 20s and even I've noticed a huge difference in summer air clarity the past 5-ish years compared to growing up in the late 90s/00s. Code red and orange days were pretty regular and would often last for days in a row. That combined with mild asthma really made me hate summer sports. I can't remember a stretch like those recently though.
DCA reported Mod Snow at the onset of precip. There's a sudden temp/dew drop, pressure jump, and then a subsequent rebound around the same time. What am I seeing here, computer error? Glitch in the matrix?