Earlier today, Civil Protection warned everybody in Iceland that dust masks had to be used throughout the country due to unpredictability of wind direction. A few minutes ago, a new announcement was issued telling that dust masks will be necessary only where ashes are visible. Composition of the ashes are still being investigated, but there are chances that they may contain fluorine, which can be toxic.
And if you cannot find dust masks anywhere, here is a nice How-To for you. Basically, if you have a cloth and water, you should have a pretty nice dust mask already.
For the time being, there is just a lot of rain in Reykjavík city. And in case you were wondering, nobody seems really worried around here, and nobody is wearing any dust mask.