But few realize that we are all adversely affected by a pollutant so common that it tends to be overlooked.
What is the grammatical name and function of the bolded part?
closed as off-topic by Janus Bahs Jacquet, Christi, Hellion, choster, user49727 Nov 28 '13 at 17:20
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It's a subordinate clause.
That that after realize is a dead giveaway. In fact it's called a "subordinating that". The Wikipedia article mentions a couple more of such "dependent words".