Scientists across the Pacific Northwest are investigating a rain that left a residue on cars in two states.

The “milky rain” fell on both Oregon and Washington states, leaving a powdery resident on vehicles and buildings.  Samples have been collected by the Pacific Northwest National Laboratory and the Benton Clean Air Agency in an attempt to discover what was in the rain.

So far the scientists have competing theories.  One is that a volcanic eruption in Japan has resulted in volcanic ash mixing with clouds to create the rain.  The other is that dust from central Oregon somehow mixed with a storm.

The National Weather Service has taken a mostly impartial view, stating dust storms were the likely cause but it could not rule out volcanic ash.  The NWS says they do not have the equipment necessary to analyze the rain and discover its origin.

Robin Priddy of Benton Clean Air says that air monitoring stations detected nothing during the rain but that they don’t feel it poses a health risk.

“We don’t have any reason to think there’s anything wrong, but there’s no reason not to be cautious if you’re concerned,” she added. “You may want to wash it off your car with water, rather than with your hands, and avoid touching it and breathing it in.”