There are probably a few areas on Earth untouched by air pollution, but for the rest of us, knowing what kind of haze to expect can mean the difference between a perfect shot and a weekend of frustration. Because landscapes are probably the most recorded subject in time-lapse, I want to point to a reference website that might help.
This site is run by the Environmental Protection Agency (EPA) and collects information from many regional sources and even Canada. My favorite feature is the Visibility Cameras link in the bottom right of the front page. This leads to a list of webcams with live views from around the country. Some of the cameras even offer historical examples of what to expect on clear and hazy days.
This information is worth a peek the next time you’re headed out for a day of shooting or scheduling a trip to a national park. We all know to check for clouds, fog, rain, and snow, but air quality is perhaps even more important. I’ve captured some great shots in many different weather conditions but haze and smog almost always leave me disappointed.
AIRNow also offers Android and iPhone apps for free with national maps and regional information.