There will be more than 16,000 fireworks in the United States during the fourth of July celebration - enough to register a dramatic (albeit temporary) effect on air quality.

In its publication, the citylab website explains how all these rockets and explosions emit considerable amounts of "fine particulate matter", microscopic particles capable of penetrating deep into the lungs and blood.

Another publication reveals how some states will fight the problem. By contrast, pollution levels in the US are generally half of the average in Bulgaria, but even for one-time rises - at the time of their national holiday, they are looking for cleaner alternatives.