The most difficult air riddles

Delta Air Lines, Inc. (NYSE: DAL), commonly referred to as Delta, is a major American airline, with its headquarters and largest hub at Hartsfield–Jackson Atlanta International Airport in Atlanta, Georgia. In 2013, Delta Air Lines was the world's largest airline in terms of scheduled passengers carried (120.6 million).

St. Elmo's fire is a form of plasma. The electric field around the object in question causes ionization of the air molecules, producing a faint glow easily visible in low-light conditions. Conditions that can generate St. Elmo's fire are present during thunderstorms, when high voltage differentials are present between clouds and the ground underneath. The nitrogen and oxygen in the Earth's atmosphere cause St. Elmo's fire to fluoresce with blue or violet light; this is similar to the mechanism that causes neon lights to glow

The most important gas which leads to acidification is sulfur dioxide, coming from fossil fuel combustion and industry (and, in lesser amounts, from volcanoes and wildfires). In recent years, emissions of nitrogen oxides which are oxidized to form nitric acid are of increasing importance due to stricter controls on emissions of sulfur containing compounds.