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Atmospheric Environment


Radiation fog samples have been collected at a rural site in Central Pennsylvania from 2007 through 2015 in order to document chemical composition, assess concentration changes over time, and to provide insight into emission sources that influence the region. The collection of samples over multiple years makes this one of the few long duration radiation fog studies that have been completed. During the course of the campaign, 146 samples were obtained and analyzed for pH, major inorganic ions, low molecular weight organic acids, total organic carbon (TOC) and total nitrogen (TN). Ammonium (median concentration = 209 μN), sulfate (69 μN), calcium (51 μN), and nitrate (31 μN) were the most abundant inorganic ions, although these were present at much lower concentrations than for radiation fog studies conducted in other locations. Organic acids, of which formate (20 μM) and acetate (21 μM) were the most abundant, were closer in magnitude to measurements made during previous studies. Organic acids accounted for 15% of TOC, which had a median concentration of 6.6 mgC l-1. The median concentration of TN was 3.6 mgN l-1, 18% of which was determined to be organic nitrogen. Statistically significant decreasing trends from 2007 to 2015 were noted for sulfate, ammonium, chloride, and nitrate. For the same period, an increase in pH was observed. Seasonal trends were identified for a number of species as well. The partitioning of ammonia between the gas and aqueous phases was also investigated and found to deviate significantly from equilibrium.


Derek J. Straub, Radiation fog chemical composition and its temporal trend over an eight year period, Atmospheric Environment, Volume 148, January 2017, Pages 49-61, ISSN 1352-2310,