SANTA ROSA -- January commercial passenger volume at the Charles M. Schulz--Sonoma County Airport was 2.4 percent higher than a year before and up 33.9 percent since the same month in 2008 after airline service returned.

A total of 15,034 passengers flew Horizon Air, the airport's only commercial carrier, in January. Volume was nearly equal for flights that originated in Santa Rosa and flights that originated elsewhere: 49.7 percent flew to Santa Rosa and 50.3 percent to one of the airport's four destinations in the western United States.

Inbound passenger volume has historically trailed slightly behind flights originating in Santa Rosa, but airport officials have said the rising proportion of inbound flyers could point to an improving local economy and appeal for tourism. The proportion was equal for January 2012, compared with 48.8 percent inbound passengers in January 2008.

Horizon Air, a subsidiary of Alaska Air Group (NYSE: ALK), began offering commercial flights at Sonoma County Airport in March 2007. The regional carrier offered more than 150 flights last month, up 13.4 percent versus last year.

The carrier offers five flights a day from Santa Rosa to Portland, Seattle, Los Angeles and San Diego. Citing rising passenger volume, Horizon has committed to an additional Los Angeles flight this summer.