The chemistry of intercepted clouds in Northern Arizona during the North American monsoon season

James W. Hutchings, Marin S. Robinson, Heide McIlwraith, Jennifer Triplett Kingston, Pierre Herckes

Research output: Contribution to journalArticlepeer-review

45 Scopus citations


Cloudwater samples have been collected for the first time at a high-elevation site in the US interior Southwest. Cloud samples were collected at the summit of Mt. Elden near Flagstaff, Arizona. The samples were analyzed for pH, ionic composition, trace metals, organic carbon content, and volatile organic compounds. All of the samples showed high pH values (5.12-6.66), which appear to be the result of soil/crustal acid-neutralizing components. Ammonium and nitrate were the dominant ionic species. Organic carbon concentrations ranged from 3 to 18 mg/l. Volatile aromatic compounds (toluene, ethylbenzene, and xylenes) were detected, although they did not contribute significantly to the dissolved organic matter (<1% of dissolved organic carbon). Still, their aqueous-phase concentrations were substantially higher than equilibrium partitioning from the gas phase would suggest. Metal concentrations were high when compared to other cloud studies in remote areas. Overall, with the exception of pH, the cloud chemistry showed marked inter-event variability. The source of the variability was investigated using NOAA HYSPLIT dispersion calculations. Like the cloud composition, the air mass back trajectories differed widely from event to event, and consistently, air masses that passed over highly urbanized areas had higher trace metal, organic, and ion concentrations than more pristine air masses.

Original languageEnglish (US)
Pages (from-to)191-202
Number of pages12
JournalWater, Air, and Soil Pollution
Issue number1-4
StatePublished - May 2009


  • Acid rain
  • Cloud
  • Cloud chemistry
  • Secondary organic aerosol formation
  • Volatile organic compounds

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Ecological Modeling
  • Water Science and Technology
  • Pollution


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