Twitter's (TWTR - Get Report)  share of the U.S. mobile advertising industry will decline to 2% in 2017 from 2.6% in 2016, according to a new study released on Tuesday by eMarketer

That equates to approximately $1.15 billion in mobile ad revenue for Twitter in 2017, compared to $1.21 billion in 2016.

This is the first time eMarketer has projected a decline in Twitter's mobile ad revenue.