Food labels can contain all sorts of guidance for you to help decide which products to choose. You may have seen Packaged in a protective atmosphere or modified atmosphere printed on many products; this does not mean that the product is packaged in a clean warehouse.
What this actually means is that the gas inside the packaging has been modified, often by removing the oxygen that is normally found in the air. The Oxygen (O2) is frequently replaced with Nitrogen (N2) or Carbon Dioxide (CO2) which can extend the life of the food, prevent oxidisation of the product which can cause a change in colour and taste and prevent bacterial growth.
A great benefit of a modified atmosphere is that this also reduces the need for additives. Once the packaging is opened the small amount of gas is quickly released and replaced with natural air.