With what some may see as jaw-dropping cheek, a new government-funded study of ozone pollution in western North America has concluded that it's all Asia's fault.
This could make it more difficult for the United States to meet Clean Air Act standards for ozone pollution at ground level, says the report, regretfully.
"In springtime, pollution from across the hemisphere, not nearby sources, contributes to the ozone increases above western North America," said lead author Owen R Cooper, of the NOAA-funded Cooperative Institute for Research in Environmental Sciences at the University of Colorado. "When air is transported from a broad region of south and east Asia, the trend is largest."
The team used historical data of global atmospheric wind records and computer modeling to match ozone measurements from the last 26 years with the air-flow patterns of the preceding few days. This let the scientists track ozone-producing emissions back to a broad region of origin.
The researchers say they used springtime measurements because previous studies indicated that was when they were most likely to find ozone being transported from Asia to the US.
They found that when the dominant airflow came from south and east Asia, the scientists saw the largest increases in ozone measurements. When winds weren't directly from Asia, ozone still increased but at a lower rate, implying that emissions from other places might also be sneaking into North America.
While they found evidence that North American fossil fuel emissions do contribute to global ozone levels (never!), they concluded that these local emissions aren't directly causing the rise in ozone above western North America.
Presumably, they're going elsewhere: maybe the Chinese government is right now commissioning a report into how ozone levels in late summer are all caused by winds from the US.
The full report appears in Nature.