SANTA ROSA -- Commercial airline passenger volume at Charles M. Schulz--Sonoma County Airport north of Santa Rosa increased 15.8 percent in May from a year before and 16.4 percent from April.

In April, just over 16,000 passengers traveled to and from the airport. In May, that number increased to more than 18,000, according to monthly report from Horizon Air, the only such airline serving Santa Rosa.

From April to May 2010, just more than 15,000 passengers went through the airport, according to Horizon.

The total passenger counts were split virtually equally between passengers leaving the airport and arriving, though the amount leaving was slightly higher.

January and February of this year both had 18 percent year-over-year increases, though the passenger totals for those months were much lower than in March and April, according to Horizon figures.