Perfect Market, a marketing firm for publishers, launched its Vault Index today, revealing the most “valuable” topics in online news in terms of ad revenue per page view. Its findings are a bit counterintuitive. While coverage of celebrity scandals were the topics that attracted the most online traffic, more serious news topics brought in the most ad clicks.

Here are the most valuable news topics for Summer 2010, according to the Perfect Market press release:

1. Unemployment Benefits
2. Gulf Recovery Jobs
3. Egg Recall
4. Gulf Oil Spill
5. Mortgage Rates
6. Jobs
7. Obama
8. Social Security
9. Immigration Reform
10. Proposition 8

The firm compiled this list by tracking “more than 15 million news articles from 21 U.S. news sites,” from mid-June to mid-September. It calculated each topic’s advertising revenue per thousand page views (RPM). While stories about the egg recall gave a return of $20 or so RPM, articles on the Lindsay Lohan sentencing averaged an RPM of $2.50.

As Perfect Market’s CRO Tim Ruder writes on the company blog, the common assumption that hard news stories are “loss leaders” is incorrect; these topics that most news sites see as their mission to cover are producing significant revenue. The reason, as he told Jeremy Peters of The New York Times, is that hard news stories are easier to pair with contextual ads. Someone reading a story about mortgage rates might be likely to click on an ad for a mortgage broker. The same isn’t true of a story about Lindsay’s latest exploits.

Lauren Kirchner is a freelance writer covering digital security for CJR. Find her on Twitter at @lkirchner