SAN FRANCISCO — Newspapers’ financial woes worsened in the second quarter as advertising sales shrank by 29 percent, leaving publishers with $2.8 billion less revenue than they had at the same time last year. It’s the deepest downturn yet during a three-year free fall in advertising revenue — newspapers’ main source of income. The magnitude of the industry’s advertising losses have intensified in each of the last 12 quarters. The numbers released Thursday by the Newspaper Association of America weren’t a shock, given the dramatic erosion mirrored the advertising losses that the largest U.S. newspaper publishers already had reported for the April-June period. Still, the statistics served as a stark reminder of the crisis facing newspapers as they try to cope with a brutal recession and advertising trends that have shifted more marketing dollars to the Internet. ‘This data represents a rearview-mirror perspective on what we all know was a terrible stretch of bad road,’ said John Sturm, chief executive for the newspaper association that serves as the industry’s largest trade group. The latest turbulence left U.S. newspapers with ad sales of $6.8 billion in this year’s second quarter compared to $9.6 billion last year. […]