Chemistry of organic nitrogen in atmospheric waters and fine particles.

摘要

Although a few past studies have found significant quantities of organic nitrogen (ON) in precipitation and dry deposition, not much is known about the atmospheric concentrations, composition, and environmental fates of these compounds. To fill in this gap, this study has focused on quantifying, speciating and characterizing the photochemical transformations of ON compounds in atmospheric water drops and fine particles (PM_2.5).; PM_2.5 and wintertime fog waters collected from Davis, California were analyzed for inorganic nitrogen species (i.e., NH₄ +, NO₃−, and NO₂ −), ON and free and combined amino compounds. Significant amounts of organic and inorganic N were measured in both types of samples—ON typically accounted for ∼20% of the total N and ∼20% of the total PM_2.5 mass. Amino compounds, predominantly in combined forms, generally represented ∼20% of the ON in PM_2.5 and fog waters.; We also examined transformations of ON compounds and the simultaneous formation of inorganic N species such as NO_x, HNO₃/NO ₃−, and NH₃/NH₄+ in fog waters during sunlight illumination and O₃ exposure. Generally ON was destroyed at initial rates of ∼20 μM per hour, while NH ₄+, NO₃− and NO _x were formed at rates on the order of a few μM per hour. This phototransformation of ON is a previously unrecognized pathway for producing inorganic N in the atmosphere and might significantly affect atmospheric chemistry and the bioavailability of atmospheric deposition.; Another facet of this study was to explore the possible sources of atmospheric nitrogen and phosphorus to a once pristine aquatic ecosystem—Lake Tahoe, California/Nevada. By characterizing the concentrations and speciation of airborne N and P along a transect from the Central Valley of California to the Tahoe basin and at the edge of a forest fire plume, we found that the Central Valley might be a significant source of N to the Tahoe basin during summer and that forest fires could be a significant source of atmospheric N and P to the lake.; Our findings indicate that ON compounds likely play important roles in tropospheric chemistry and that the deposition of ON might significantly affect nutrient balances in ecosystems.