Asian ozone pollution in Hawaii is tied to climate variability

Jan 27, 2014 by Joanne Curcio
Asian ozone pollution in Hawaii is tied to climate variability
Asian pollution drifts east toward North America in 2010. Hawaii is denoted by the star. Credit: Nature Geoscience

(Phys.org) —Air pollution from Asia has been rising for several decades but Hawaii had seemed to escape the ozone pollution that drifts east with the springtime winds. Now a team of researchers has found that shifts in atmospheric circulation explain the trends in Hawaiian ozone pollution.

The researchers found that since the mid-1990s, these shifts in have caused Asian reaching Hawaii to be relatively low in spring but rise significantly in autumn. The study, led by Meiyun Lin, an associate research scholar in the Program in Atmospheric and Oceanic Sciences (NOAA) at Princeton University and a scientist at the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory, was published in Nature Geoscience.

"The findings indicate that decade-long variability in climate must be taken into account when attributing U.S. surface trends to rising Asian emissions," Lin said. She conducted the research with Larry Horowitz and Songmiao Fan of GFDL, Samuel Oltmans of the University of Colorado and the NOAA Earth System Research Laboratory in Boulder; and Arlene Fiore of the Lamont-Doherty Earth Observatory at Columbia University.

Although protective at high altitudes, ozone near the Earth's surface is a greenhouse gas and a health-damaging air pollutant. The longest record of ozone measurements in the U.S. dates back to 1974 in Hawaii. Over the past few decades, emissions of ozone precursors in Asia has tripled, yet the 40-year Hawaiian record revealed little change in ozone levels during spring, but a surprising rise in autumn.

Through their research, Lin and her colleagues solved the puzzle. "We found that changing wind patterns 'hide' the increase in Asian pollution reaching Hawaii in the spring, but amplify the change in the autumn," Lin said.

Climate shifts and a sudden rise in Asian ozone pollution reaching Hawaii during autumn in the mid-1990s onwards are documented in the figure. Shown are tracer of Asian pollution in 2010 (the inset map) and times series of autumnal ozone anomalies at Mauna Loa, Hawaii, for 1975 to 2012 as observed (black) and simulated by a chemistry-climate model with constant (red) and time-varying (purple) emissions of ozone precursors. Credit: Nature Geoscience

Using chemistry-climate models and observations, Lin and her colleagues uncovered the different mechanisms driving spring versus autumn changes in . The findings indicate that the flow of ozone-rich air from Eurasia towards Hawaii during spring weakened in the 2000s as a result of La-Niña-like decadal cooling in the equatorial Pacific Ocean. The stronger transport of Asian pollution to Hawaii during autumn since the mid-1990s corresponds to a positive pattern of atmospheric circulation variability known as the Pacific-North American pattern.

"This study not only solves the mystery of Hawaiian ozone changes since 1974, but it also has broad implications for interpreting trends in surface ozone levels globally," Lin said. "Characterizing shifts in atmospheric circulation is of paramount importance for understanding the response of surface to a changing climate and evolving global emissions of ozone precursors," she said.

Explore further: Air pollution tied to exports: Study finds blowback causes extra day per year of ozone smog in LA

More information: Meiyun Lin, Larry W. Horowitz, Samuel J. Oltmans, Arlene M. Fiore, Songmiao Fan. Tropospheric ozone trends at Mauna Loa Observatory tied to decadal climate variability. Nature Geoscience, Published Online: 26 January, 2014, dx.doi.org/10.1038/ngeo2066

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alfie_null
not rated yet Jan 28, 2014
Regarding the graphic depicting ozone over the Pacific and N. America, it would be interesting to see it expanded to cover the rest of the world. It would also be useful to know the significance of the different colors. For instance, what scale.
ViperSRT3g
not rated yet Jan 28, 2014
I wonder if it's related to Hawaii's annual wave activity. In the summer time, Hawaii gets larger waves on the southern beaches of all the islands. During the winter time, the larger waves come from the northern shores. This correlates to the data obtained in this study.

Pollutants are masked during the spring due to greater wind flow to the north from the south. Pollutants are increased during the fall due to greater wind flow to the south from the north.

Ask anyone who has or still does live in the Islands about the waves. Chances are, they'll be able to tell you about the wave cycles throughout the year.