Learn about N95 Filters and how the CDC classifies them here (these are technically filters, not respirators.) These offer you good protection against bacteria exposure.

Also there is likely to be all kinds of particulates in the air if there is a fire or collapsed buildings or what have you. These masks will filter out a lot of bad stuff. They won't protect you from smoke or chemical attack so keep your expectations correct, but they are a must have item.

During pandemics, supplies get scarce. You can see if Amazon or eBay has any, otherwise read our article where to find n95 or kn95 masks.

To read more about Respirators and Gas Masks, read this article.