The CO transport over the North Pacific is a phenomenon that occurs every spring (March & April). The source is Eastern Asia, mainly China and the target is West of North America (USA and Canada). MOPITT has been observing this event every year since the beginning of the mission in 2000. The pathways of CO transport is most likely along the border between Aleutian Low and Pacific High, a quasi permanent cyclonic-anti-cyclonic structure.
Direction of wind as well as the time to cross the ocean confirms what we can observe with MOPITT (daily plots of CO tot col.). So, a typical spring event of CO transport in North Pacific takes around a little bit more than one week to cross the Pacific. Using a larger time window (monthly instead of daily) for averages it is easy to observe that the spring CO transport band is interrupted around longitude 250 at the location of the Rockies Mountains which play the role of ‘pollution barrier’.