1 July 2006  |  Daniel Rosenfeld and Amir GivatiThe Hebrew University of Jerusalem, Jerusalem, Israel

The decreasing trend in coarse aerosols (the coarse aerosols may act to initiate and enhance precipitation), in conjunction with the constancy and/or increases of the small aerosols (small aerosols suppress precipitation), can explain the continuing decreases in orographic precipitation during the last two decades… 

Link To Evidence of Orographic Precipitation Suppression by Air Pollution–Induced Aerosols in the Western United States