Tiny, Long-Distance Travelers

We’ve written in Erosion Control magazine for years about the problem of airborne dust, and even the ways in which distant events—a sandstorm in the Sahara Desert, say—can deposit sediment particles thousands of miles away. A new study shows that the long-distance air-quality problem might be more widespread than previously realized.

Even though the US has implemented more stringent air-quality measures for the last few decades, including curbing emissions from vehicles and factories, smog has been getting worse, particularly in the Western states. A study by researchers from Princeton University and NOAA’s Geophysical Fluid Dynamics Laboratory shows that the source might be air pollution originating in parts of Asia.

The researchers looked at smog, defined as ground-level ozone, from the 1980s to the present. Although during that period the US has decreased its production of nitrogen oxides and other chemicals that cause smog, several Asian countries have tripled their collective output, including China, India, Japan, North Korea, and South Korea. Winds—especially in the spring—carry the chemicals across the Pacific Ocean to the Western US, where spring ozone levels have increased by 5 to 10 parts per billion. Those levels remain elevated even in other seasons when the wind patterns have changed. The federal ozone standard is 70 ppb.

Chemicals like nitrogen oxides might be easily carried on the wind, but they’re just one part of the air-quality picture. As our article notes, “Anywhere from about 990 to 1,650 tons of soil dust enters the world’s atmosphere each year. In fact, dust in the air has been fingered as one possible suspect in atmospheric instability and climate change—no small feat for tiny pieces of soil with an aerodynamic diameter of 10 microns or less. That’s so small that several hundred 10-micron particles could fit into the period at the end of this sentence.” Sand from the Sahara has been shown to travel west across the Atlantic, ending up in New England. Dust from China and Mongolia has also been documented to reach as far as the Midwestern US and parts of Canada.

The lead researcher on the recent study, which was published in Atmospheric Chemistry and Physics this month, believes we need to maintain a global perspective as we develop strategies in the US to meet air-quality objectives. Given that we can’t regulate other countries’ dust control efforts or ozone emissions—any more than they can regulate our carbon emissions or other environmental efforts—what do you think is a reasonable approach to taking them into account?