Transport of Air Pollution from Asia to North America
There are a number of implications of these results. For example, those measuring atmospheric chemistry over NA typically have very little information about potential significance of trans-Pacific transport, particularly on short time scales when most measurements are taken. Our results suggests that NA aerosol and chemical data may need to be reconciled with intercontinental transport to explain synoptic-scale variability, particularly for enigmatic high episodes that appear to have no local origin. For regional scale chemical modeling that relies on static or monthly averaged boundary conditions for either Pacific air or descending free tropospheric air over NA, this study provides insight into the potential synoptic-scale consequences of these boundary condition assumptions. Results presented in this paper suggest that regional scale models that pose static chemical boundary conditions for Pacific “background” air may suffer from unexplained variability in tracer time series when compared to observations. Finally, from an ozone policy perspective there could be significantly different consequences of an Asian ozone signal that arrives as a smooth constant background increase, versus one that arrives episodically as a mixture of weak and strong events. Episodes that contribution 40 ppb of ozone to surface ozone levels in NA due to Asian emissions are certain to exacerbate local pollution events and contribute significantly to the frequency of elevated (80 – 100 ppb) ozone exposures. This is especially of concern in elevated areas more frequently exposed to free tropospheric air.
We invite the reader to the following web site [http://www.cgrer.uiowa.edu/asiaimpact] that contains a number of related animations of trans-Pacific transport.
KeywordsAsian Dust Geophysical Fluid Dynamics Laboratory Free Troposphere North America Asian Emission
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