Greg Sterling / Marketing Land: IAB and PwC: US online ad spending reached $57.9B in H1 2019, up 16.9% year-over-year but lower than the 23.1% growth in the same period last year  —  Mobile ad revenues were $39.9 billion or 69% of the total.  —  U.S. online ad spending reached $57.9 billion, representing growth of 16.9% year-over-year …