Photodestruction of Dissolved Organic Nitrogen Species in Fog Waters

Despite the fact that significant quantities of organic nitrogen (ON) have been measured in rain drops and aerosol particles, relatively little is known about the chemical and photochemical reactivity of ON species in tropospheric condensed phases. The preliminary work presented here reports on the photode struction of a number of dissolved organic nitrogen (DON) species in illuminated fog waters collected in Davis, CA. Results from these experiments show that a number of DON compounds, including pyrrole, methionine, and tryptophan, are rapidly destroyed in illuminated fog waters. Calculated half-lives for these compounds in fog waters illuminated with midday, winter-solstice sunlight range from 0.6-2.3 h. The other DON compounds studied were destroyed more slowly; half-lives in winter-solstice sunlight ranged from ∼10 to over 48 h. Indirect photooxidation as a result of photoformed reactive species was the dominant mechanism for destruction of the DON species examined. Hydroxyl radical was a minor sink for the DON compounds that were most rapidly photodestroyed but was a significant sink for the amino acids which had longer lifetimes. The destruction of ON in these experiments indicates that tropospheric photoreactions might play a significant role in the biogeochemical cycling of nitrogen and likely increase the bioavailability of nitrogen in atmospheric deposition.