Asian pollution affects air quality in west coast USA

Airborne pollution blown across the Pacific Ocean is having a much greater impact on American air quality than previously thought, according to Californian academics.

Atmospheric scientists from the University of California’s David Campus have been monitoring aerosols at three sites in the state – one at sea level, another on a coastal mountainside and another high on the slopes of inland mountains.

Although the term has become associated with spray cans in every-day parlance, aerosols are in this sense any number of tiny airborne particles of solids or liquid that can remain suspended in the atmosphere for long periods.

Most aerosols are of natural origin but many others are produced as industrial emissions or from other manmade sources such as burning fossil fuels for transport.

While it has long been known that smog from emerging economies in Asia can, on occasion, reach the shores of North America the study shows that this situation is actually the rule rather than the exception.

The sampling at sea level produced results that were pretty much in keeping with conventional wisdom – that most aerosols were either natural marine particles or from local industry with occasional waves of particles being blown in from Asia during unusual weather events.

But those taken on the higher ground told a very different story.

In the words of the report: “Throughout the experiment the aerosols in the lower free troposphere over the northeastern Pacific Ocean and western North America were dominated by continental outflow from Asia, with little marine or North American continental influence.”

In other words, the majority of the aerosols could be traced back to China and other emerging economies.

According to the authors of the study, the findings are likely to affect attempts to clear hazy skies over much of the US and to understand how growing Asian air pollution will influence global climate change.

“Occasional, large-scale Asian dust storms had led us to believe that this pollution travelled east in infrequent, discrete events,” said UC Davis atmospheric scientist Steve Cliff.

“As it turns out, Asian pollution, particularly in the Sierra-Cascade range and elsewhere in the American West, is the rule, not the exception.”

That may make it hard to meet air-quality goals set by the federal Clean Air Act, Cliff said.

“Assuming Asia continues to develop as predicted, with commensurate energy needs from combustion, we will continue to increase our ‘background’ haze in the US,” he said.

It also may change the prevailing notions of long-range aerosol transport, which are used by scientists trying to predict climate change using computer models, he said.

The lead author on the new study is Tony VanCuren, an atmospheric scientist at UC Davis and the California Air Resources Board.

The co-authors are Cliff; Michael Jimenez-Cruz, a former UC Davis student and now a researcher at the Advanced Light Dest at Lawrence Berkeley National Laboratory; and Kevin Perry, a former UC Davis postdoctoral scholar, who is now an assistant professor of meteorology at the University of Utah.

That experiment used innovative air-sampling machines developed by UC Davis’ DELTA research group (for Detection and Evaluation of Long-Range Transport of Aerosols).

The new samplers allow researchers to collect airborne particles continuously and to analyze them in short time steps and over multiple size ranges.

That made it possible to do the new analysis, which resolves relationships between pollutants and weather in much greater detail.

An abstract of the study can be found by following the link.

Sam Bond

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