The hourly pollen counts during one epidemic showed that the amounts of grass pollen grains trapped in the thunderstorm outflow were between four and 12 times higher than elsewhere. Emergency calls were registered within half an hour of an outflow being recorded. Admission rates for asthma were not pushed beyond expected levels during thunderstorms without outflows, and a cold front of air by itself had no significant impact on admission rates. The authors conclude that the powerful action of a thunderstorm outflow sweeps up ruptured and intact pollen grains and forces them into a band of air rising up to 1 km above ground. Asthmatics who breathe in this super concentrated mix of allergens experience an acute airways response.
Thunderstorm outflows preceding epidemics of asthma during spring and summer.
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