The S.C. State Ports Authority is proud of its ongoing efforts to reduce air emissions by helping truck owners replace their old diesel rigs with more fuel-efficient trucks. It should be proud. Going the extra mile to improve local air quality is laudable.

Since 2011, the SPA has given 57 local truckers money to help them upgrade. With a recently awarded DHEC grant for $145,000 to supplement $145,000 from the SPA itself, and the scrap value of about $2,000 a truck, the SPA hopes to persuade 29 more truck drivers to follow suit.

If only the SPA were as eager to cut air emissions from cruise ships idling at our dock. Both the state and the Charleston medical societies have gone on record with their concerns about cruise ship air pollution.

The Coastal Conservation League, which has been supportive of the truck replacement program, estimates that the Carnival Fantasy, if it is in town 70 times a year, would produce an amount of sulfur dioxide equivalent to more than two million trucks.

Following that logic, for an upfront cost of about $5 million for shoreside power, the SPA could take two million “trucks” off the road.

Perhaps the Environmental Protection Agency (the source of the DHEC truck grant) would help with the shoreside power cost. The SPA has identified 132 trucks that need replacing. If efforts are successful, 85 percent of rigs built before 1994 that regularly call at SPA container facilities will be gone by the end of the year.

And with those trucks goes 34 percent of diesel particulate pollution.

The SPA’s commendable effort to reduce truck emissions is not to be discounted. It will make a significant difference in air quality for workers and residents.

But the SPA could make much more difference by installing shoreside power and requiring cruise ships to plug in while they’re visiting Charleston.