Does Asian dust and pollution transport only occur when there is a major dust storm in Asia?
No! This is just when the newspapers like to cover it! The pollution sources in Asia are on all the time. There is probably a small amount of pollution that gets transported across the Pacific all the time. The large dust storms only occur when high surface winds are present and when the soil is relatively dry. This usually happens after a frontal passage and is most common in spring. The large dust particles get picked up and the resulting concentrations in Asia can be enormous. Fortunately, such high levels do not persist for long. The larger dust particles fall-out over time, are removed by rain and disperse, so that the concentrations are decreasing with time. Nonetheless, occasionally we do see very high aerosol levels from Asian dust storms.
