Could a reported rainfall pH of 3.1 actually be realistic? In this Chemistry question Is there any reason to fear personal exposure to rain with a pH of 3.1? I haven't gotten any answer, but there was some discussion about the reality of the measurement. 

So I'll ask here, is a sustained rainfall with a pH of roughy 3.1 possible on Earth? Of course it would have to be related to some serious sources of pollution - perhaps intensive coal burning over a large geographic region. I say 'sustained' to rule out any fluke or highly unusual situations. Could I really fill a plastic bucket with a substantial amount of pH 3.1 water by putting it outdoors, under the sky, in the rain, in the right place on Earth?

Oh, for this question I'd like to exclude unusual situations related to volcanic eruptions as well.
A quick literature search seems to confirm Gordons estimation, even at the scale of a whole bucket:


  [T]he annual mean pH, based upon
  samples collected weekly during 1970-1971 and weighted proportionally to
  the amount of water and pH during each period of precipitation, was 4.03
  at the Hubbard Brook Experimental Forest, New Hampshire; 3.98 at Ithaca,
  New York; 3.91 at Aurora, New York; and 4.02 at Geneva, New York. Measurements
  on individual rainstorms frequently showed values between pH 3
  and 4 at all of these locations. Data from the National Center for Atmospheric
  Research included precipitation pH values as low as 2.1 in the northeastern
  United States during November 1964. 


Patel, C. K. N., E. G. Burkhardt, and C. A. Lambert. "Acid rain: a serious regional environmental problem." Science 184 (1974): 1176-1179.