Suphioglu. 1998. This is a review article that describes the ways in which grass pollen allergens in the respirable range (<5μm) may occur in the outdoor environment and how those are related to thunderstorm asthma.  Primarily, rainfall ruptures grass pollen grains, which release allergen containing starch granules.  The author also indicates the possibility of released starch granules binding to respirable diesel exhaust particles.