From what I have read once sodium nitrite is exposed to air is does convert to sodium nitrate over time- there have been many posts about this on this site. Sodium Nitrite has a chemical expression of NaNO2 and sodium nitrate has a chemical composition of NaNO3. So once sodium nitrite is exposed to air over time one oxygen atom is added to each sodium nitrite molecule and it becomes sodium nitrate. NaNO2 means a molecule composed of one atom of sodium(Na), one atom of Nitogen(N), and two atoms of Oxygen(O2). I think I read on the internet somewhere that the half life for this is 80 days, but I can't find this site now- that means in 80 days half of the nitrite will become nitrate, then over the next 80 days half of the remaining amount will become nitrate, etc. I'm not sure how accuarte this is, I am still trying to research this further.