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

Abstract

Abstract. Atmospheric aqueous chemistry can have profound effects on our environment. The importance of chemistry within the atmospheric aqueous phase started gaining widespread attention in the 1970s as there was growing concern over the negative impacts on ecosystem health from acid deposition. Research at mountaintop observatories including Whiteface Mountain (WFM) showed that gas phase sulfur dioxide emissions react in cloud droplets to form sulfuric acid, which also impacted air quality by increasing aerosol mass loadings. The current study updates the long-term trends in cloud water composition at WFM for the period 1994–2021, with special consideration given to samples that have traditionally been excluded from analysis due to inorganic charge imbalance. We emphasize three major findings: (1) a growing abundance of total organic carbon (TOC), with annual median concentrations more than doubling since measurements began in 2009, (2) a growing imbalance between the measured inorganic cations and anions, consistent with independent rain water observations, implying that a substantial fraction of anions are no longer being measured with the historical suite of measurements, and (3) a growing number of samples exhibiting greater ammonium concentrations than sulfate plus nitrate concentrations, which now routinely describes over one-third of samples. Organic acids are identified as the most likely candidates for the missing anions, since the measured inorganic ion imbalance correlates strongly with measured TOC concentrations. An “inferred cloud droplet pH” is introduced to estimate the pH of the vast majority of cloud droplets as they reside in the atmosphere using a simple method to account for the expected mixing state of calcium and magnesium containing particles. While the inferred cloud droplet pH closely matches the measured bulk cloud water pH during the early years of the cloud water monitoring program, a growing discrepancy is found over the latter half of the record. We interpret these observations as indicating a growing fraction of cloud droplet acidity that is no longer accounted for by the measured sulfate, nitrate and ammonium concentrations. Altogether, these observations indicate that the chemical system at WFM has shifted away from a system dominated by sulfate to a system controlled by base cations, reactive nitrogen species and organic compounds. Further research is required to understand the effects on air quality, climate and ecosystem health.

Suppressor and calibration standard limitations in cation chromatography of ammonium and 10 alkylamines in atmospheric samples

“…19,76 A similar ion imbalance has also been observed as an emerging trend in the chemical composition analysis of continentally-originating cloud water at Whiteface Mountain; where an increasing trend in (Σ+/Σ−) was also associated with missing anion measurements in those samples. 77…”

“…19,76 A similar ion imbalance has also been observed as an emerging trend in the chemical composition analysis of continentallyoriginating cloud water at Whiteface Mountain; where an increasing trend in (S+/S−) was also associated with missing anion measurements in those samples. 77 Two amines were unresolved in this initial analysis: DEAH + and TMAH + because the column temperature was only 35 °C, which limited the stationary phase selectivity. Compared to the other quantied amines, the analysis of DEAH + + TMAH + was found to have the highest equivalent ionic loading estimated at 2.29 neq m −3 (Fig.…”

Long-Term Monitoring of Cloud Water Chemistry at Whiteface Mountain: The Emergence of a New Chemical Regime

“…htm (Lance, 2023). The code and data used to make the figures can be found at https://doi.org/10.5281/Zenodo.7379622 (Lawrence, 2022). Acknowledgements.…”

The Chemical Landscape of Leaf Surfaces and Its Interaction with the Atmosphere

“…Particulate matter is also found in hydrometeors, although its contribution to the total carbon budget is minimal�it ranges from negligible to 35% depending on location, time of the year, and occurrence of specific events. 247,252,254 These insoluble particles include black carbon, 255,256 primary biogenic particles (e.g., bacteria, pollen, fungal spores), 257 soot (including elemental carbon), 257 soil minerals particles, 257 and microplastics. 258−260 4.2.2.…”

“…Likewise, PAHs, nitrosamines, nitrophenols, pesticides, and other anthropogenic chemicals have been detected in fog and cloudwater (reviewed by Herckes et al), with individual compounds in concentrations ranging from hundreds of ng L –1 to tens of mg L –1 (e.g., Khoury et al). Particulate matter is also found in hydrometeors, although its contribution to the total carbon budget is minimalit ranges from negligible to 35% depending on location, time of the year, and occurrence of specific events. ,, These insoluble particles include black carbon, , primary biogenic particles (e.g., bacteria, pollen, fungal spores), soot (including elemental carbon), soil minerals particles, and microplastics. − …”