Here is the full list of all 26 NERO achievements.
Complete mission : Ghost of the Past
Complete mission: The Bomber
Complete mission : The Tower
Complete mission : Hidden Cargo
Complete mission : Trapped
Complete mission : Back to School
Complete mission : On the Trail
Complete mission : 2nd Life
Complete mission : Redemption
Kill 100 enemies with only head shots
Kill Total of 500 enemies
Kill 50 enemies with sniper only
Kill 100 enemies with rifle only
Kill 100 enemies with pistol only
Kill 50 enemies with Grenades
Kill 50 enemies with explosive barrels/generators
Kill 50 enemies with mines
Kill 5 enemies with one Grenade
Complete a mission without taking damage
Complete a mission without taking any health packs
Kill every enemy in a mission
Find all the intel documents in the game
Complete a mission without being detected
Kill 50 enemies with take downs or melee attacks
Complete every mission in "Brutal mode"
Get 100% accuracy in sniper training