No you haven't. NO2 (technically N2O4) is Nitrogen Dioxide - a reddish-yellow gas that can kill you with one breath. A leak of this insidious poison did in 3 Soviet Cosmonauts some years back. They had just returned to Earth. When the ground-crew opened the capsule - all 3 were dead as doornails.

It is used as a rocket-fuel. Inhaled, it causes your lungs to fill with Nitric Acid and water - and you drown.