Influence of Asian emissions on the composition of air reaching the North Western United States

A global 3-D CTM has been used to study the impact of current and future emissions from Asia on CO, PAN and O-3 across the North Pacific. Recent measurements from Washington State have been used to verify the model results with respect to average concentrations as well as amplitude of perturbations during episodic events of strong Asian influence. By performing CTM experiments with and without anthropogenic emissions from Asia, we find that there is a significant contribution from Asian sources in the air arriving to the North Western United States, especially during spring. The mean contribution, which can not easily be inferred from the available measurements, during spring are 34 ppbv, 26 pptv and 4 ppbv for CO, PAN and O-3 respectively. The maximum enhancements caused by Asian sources during episodes are 42 ppbv, 75 pptv, and 7.5 ppbv, respectively The amplitude of the perturbations during short term (2-5 days) episodes of strong Asian influence are quite similar to springtime Asian pollution events which have recently been observed on the west coast of Washington state. A doubling of the current Asian emissions in the model yields significant enhancements in all species, though not necessarily in a linear manner.