Google has pulled back another curtain and revealed the size of its lucrative Internet ad network in the U.S. It spans more than 1.5 million advertisers and Web sites. The Associated Press calculated the figure from a state-by-state breakdown of Google Inc.’s operations that the company released Tuesday. It marks the second time in two days that Google has shared previously unknown details about the marketing channel that generates most of its revenue. The Internet search leader spelled out the commissions that it pays its ad partners for the first time Monday. The greater transparency is occurring amid increasing regulatory, political and legal scrutiny of the power that Google has amassed while building the Internet’s most profitable ad network around the Web’s most popular search engine. Tuesday’s breakdown came as part of Google’s attempt to quantify its economic impact in the U.S. The snapshot also revealed that Google has at least 12,200 workers in the U.S., primarily in California, New York and Washington state. The company employs 20,600 people worldwide. Google’s U.S. work force is probably even larger than what was listed in the report because the company didn’t specify how many employees it has in offices or data centers in six states: Iowa, North Carolina, Oklahoma, Oregon, South Carolina and Wisconsin. Besides California, New York and Washington state, the company’s report provides employees counts for Colorado, Georgia, Illinois, Massachusetts, Michigan, Pennsylvania, Texas, Virginia and Washington, D.C.