Radiation fog chemical composition and its temporal trend over an eight year period

Abstract

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.

Total organic carbon and the contribution from speciated organics in cloud water: airborne data analysis from the CAMP<sup>2</sup>Ex field campaign

“…Four categories of samples with different air mass history characteristics were compared, revealing a few notable features: (i) while speciated concentrations and TOC masses varied considerably between the four cases, the contributions of MCAs and DCAs (based on C mass) to TOC were remarkably similar with little variation (MCA : TOC = 16.03 %-23.66 % and DCA : TOC = 3.70 %-8.75 %); (ii) dust and sea salt tracer species were strongly correlated with most of the speciated organics for the North and East cases, suggestive of interactions between such species and coarse aerosol surfaces, as supported by past work (Stahl et al, 2020;Sullivan and Prather, 2007); (iii) for samples with limited aging (North case) based on selected chemical ratio values, adipate was more abundant and was negatively correlated with smaller carboxylic acids; (iv) BB samples exhibited the highest TOC concentrations (8342 ± 3730 ppb C) as well as significantly elevated levels of individual organics such as acetate, formate, succinate, glutarate, pyruvate, oxalate, and MSA; and (v) the Clark case had a higher variability in TOC (1181 ± 920.2 ppb C) than the North and East cases, presumably owing to a greater mix of influential sources such as fresh anthropogenic emissions (e.g., enhanced maleate) as well as the transport of biomass burning plumes from Borneo and Sumatra (e.g., enhanced succinate), dust, and spatial and temporal variances across different flights. Related to dust, Ca 2+ was only correlated with adipate in the Clark samples, which is consistent with a recent study in Metro Manila (Stahl et al, 2020) showing that adipate uniquely exhibits a prominent supermicrometer peak among organic acids, attributed to interactions with dust.…”

“…Wang et al (2018) showed that East Asian dust can get lofted up during dust storms, which could contribute to the transport to the Philippines. Previous studies have shown that organic acids adsorb more readily to dust compared with sea salt due to dust's more alkaline nature (Stahl et al, 2020;Sullivan and Prather, 2007). While Ca 2+ was correlated with 6 of the 11 organic species for this case (r = 0.70-0.96; Table S2), the magnitude of the correlations was very similar to those between either Na + or Cl − and the speciated organics.…”

“…MSA originates partly from marine emissions of DMS, but its concentra-tion was among the lowest of all species for all four cases with a mass contribution to total TOC (based on C mass) of only 0.17 ± 0.05 % in the North category (Table 3). In their analysis of aerosol data in the surface layer of Metro Manila, Stahl et al (2020) showed lower overall organic acid aerosol concentrations in the northeast monsoon season where northeasterly air masses originated predominantly from East Asia; Stahl et al (2020) also showed that those air masses were characterized by an enhancement in organic acid masses in the supermicrometer size range owing to adsorption to coarse particle types such as sea salt and dust, although with a preference for dust (Mochida et al, 2003;Rinaldi et al, 2011;Sullivan and Prather, 2007;Turekian et al, 2003). As there was no direct evidence of dust in this case because the Ca 2+…”

Long-term monitoring of cloud water chemistry at Whiteface Mountain: the emergence of a new chemical regime

“…Importantly, these are only estimates of HCO − 3 concentrations based on equilibrium with the atmosphere. There has been significant discussion on the validity of Henry's Law constants for cloud drop distributions, as several field studies note significant departures of measurements from gasaqueous phase partitioning (Pandis and Seinfeld, 1991;Winiwarter et al, 1994;Straub, 2017). It is plausible that some deviations could also exist for the carbonate system, thus leading to inaccurate HCO − 3 concentration estimates.…”

“…Routine long-term measurements of cloud water or fog water are not widely available, but other locations worldwide have seen similar long-term reductions in SO 2− 4 and/or NO − 3 concentrations with concomitant decrease in acidity, including California's central valley (Herckes et al, 2015), Pennsylvania (Straub, 2017), New Hampshire (Murray et al, 2013), the UK (Cape et al, 2015), Italy (Giulianelli et al, 2014), France (Deguillaume et al, 2014) and Japan (Yamaguchi et al, 2015;Watanabe et al, 2022). A thorough review of both long-term and short-term cloud and fog chemistry studies has been recently compiled by Isil et al (2022).…”