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Long-Term Trends in Cloud and Rain Chemistry on Mount Washington, New Hampshire


Growing season rain and cloud events were sampled between 1984–2010 at Lakes of the Clouds (LOC) (1,540 m above sea level (ASL)) which is 1.6 km SW of the summit of Mount Washington, NH (1,914 m ASL). Mount Washington's summit is in the clouds ca. 51 % of the time. All samples were measured for pH, while cations and anions were measured consistently from 1996 to 2010. Annual mean cloud and rain water hydrogen ion concentrations declined significantly from 1984–2010. Nighttime cloud and rain hydrogen, sulfate, ammonium, and nitrate ion concentrations were significantly greater compared to daytime. Ion mean concentrations declined over the 1996–2010 timeframe and more rapidly since 2005. Co-located filter-based aerosol measurement (PM2.5) at LOC had higher ratios of ammonium to sulfate in summer daytime samples post (1995–2010) full implementation of the 1990 Clean Air Act Amendments. This suggests a shift towards more neutralized sulfate aerosol dissolution into clouds with relatively more ammonium and declines in acidity. The origin of cloud water sampled, which ranges from regional fronts to orographic lower elevation air mass uplift, along with the diurnally shifting nocturnal boundary layer that often puts the LOC site in and out of the mixed layer, likely contributes to the diurnal and inter-annual variability observed.

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Funding for this work has in part been provided by multiple United States Forest Service Cooperative Agreements and the National Oceanic and Atmospheric Administration Grant (NA06OAR460029, NA06OAR4600180, and NA09OAR4590208), and to initiate the study, the Andrew W. Mellon Foundation. This work could not have been done without the many seasonal interns who have worked for the AMC from 1984 to the present. We thank the Mount Washington Auto Road for access to the road to transport equipment.

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Correspondence to Georgia L. D. Murray.

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Murray, G.L.D., Kimball, K.D., Hill, L.B. et al. Long-Term Trends in Cloud and Rain Chemistry on Mount Washington, New Hampshire. Water Air Soil Pollut 224, 1653 (2013).

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  • Acidity
  • Clean Air Act Amendments
  • Cloud and rain water chemistry
  • Montane
  • Mount Washington NH
  • Nocturnal boundary layer
  • Nitrogen
  • Sulfur