Learn Spanish (Spain): Aquí no respiramos tanta contaminación como en el centro. - We don't breathe as much pollution here as downtown.

When comparing quantities with nouns using the tanto como structure, the word tanto must match the gender and number of the noun it describes. Since contaminación is a feminine singular noun, you must use tanta.

How can I tell that contaminación is a feminine noun?

A great trick to remember is that almost all Spanish nouns ending in -ción (like contaminación, canción, or estación) are feminine. That is why it takes the feminine word tanta instead of tanto.

Why isn't the word nosotros used before respiramos?

In Spanish, the ending of the verb usually tells you who is doing the action. The -amos ending in respiramos already means 'we breathe', so adding nosotros is unnecessary here unless you want to add special emphasis.

Does el centro just mean 'downtown'?

It literally translates to 'the center', but when talking about a city or town, el centro is the standard and most natural way to say 'downtown' or 'the city center'.