precipitation chemistry data



Precipitation samples are collected using the wet side of an automatic wet-dry collector. The collector uses a moisture sensor that causes a motor to remove a cover from a clean bucket when it senses precipitated moisture. Samples are collected on an event basis; an event is defined as continuous precipitation that has not been interrupted by more than 6-hours. At the end of an event, the sample is collected, weighed, and transferred to a labeled sample bottle. If the sample is frozen, it is allowed to sit at room temperature until the entire sample is melted. After the sample is bottled, it is analyzed at the Cary Institute analytical laboratory for pH, sulfate, nitrate, ammonium, phosphate, chloride, sodium, calcium, magnesium and potassium ions. See Table 1 for analytical methods. If the quantity of sample is insufficient for all of these analyses, as many of the analyses as possible are completed with preference given to pH, sulfate, nitrate and ammonium in that order. The precipitation collector is located in a flat, open field at an elevation of 128 m. GPS coordinates for the site are: N41.785823 W073.741447.

In 1999, we changed the sample-handling protocol as follows. A 60-ml aliquot of sample is preserved with 2 drops of chloroform and refrigerated. This aliquot is analyzed for phosphate, ammonium, and nitrate. Comparisons of phosphate, ammonium and nitrate were made for one year between samples treated with chloroform and samples left untreated. There was no significant difference between treated and untreated samples for ammonium and nitrate, but phosphate was higher in samples treated with chloroform. We made no adjustments to data collected prior to 1999. For estimation of monthly volume-weighted mean concentrations and total deposition, values that are below detection limits are replaced with one half of the detection limit. Datasets include monthly volume-weighted means and monthly total deposition.


  • YEAR Year during which event ended
  • MONTH Month during which event ended
  • #EVENTS Number of events during that month
  • VOL_CM Total volume of precipitation during that month (cm)
  • CA_DEP Calcium ion deposition (g/ha)
  • CL_DEP Chloride ion deposition (g/ha)
  • K_DEP Potassium ion deposition (g/ha)
  • MG_DEP Magnesium ion deposition (g/ha)
  • NA_DEP Sodium ion deposition (g/ha)
  • NH4_N_DEP Ammonium_N deposition (g/ha)
  • NO3_N_DEP Nitrate_N ion deposition (g/ha)
  • PO4_DEP Phosphate ion deposition (g/ha)
  • SO4_DEP Sulfate ion deposition (g/ha)
  • H_DEP Hydrogen ion deposition (g/ha)
  • CA_VWM Calcium ion volume-weighted mean (mg/L) (DL 0.01 mg/L)
  • CL_VWM Chloride ion volume-weighted mean (mg/L) (DL 0.02 mg/L)
  • K_VWM Potassium ion volume-weighted mean (mg/L) (DL 0.01 mg/L)
  • MG_VWM Magnesium ion volume-weighted mean (mg/L) (DL 0.01 mg/L)
  • NA_VWM Sodium ion volume-weighted mean (mg/L) (DL 0.01 mg/L)
  • NH4_VWM Ammonium ion volume-weighted mean (mg/L) (DL 0.02 mg/L)
  • NH4_N_VWM Ammonium_N volume-weighted mean (mg/L) (DL 0.02 mg/L)
  • NO3_VWM Nitrate ion volume-weighted mean (mg/L) (DL 0.02 mg/L)
  • NO3_N_VWM Nitrate_N volume-weighted mean (mg/L) (DL 0.02 mg/L)
  • PO4_VWM Phosphate ion volume-weighted mean (mg/L) (DL 0.002 mg/L)
  • SO4_VWM Sulfate ion volume-weighted mean (mg/L) (DL 0.02 mg/L)
  • H_VWM Hydrogen ion volume-weighted mean (mg/L)


  • Precipitation sample collection 1983-2008 Aerochem Metrics, Model 301, Automatic Sensing Wet/Dry Precipitation Collector, 2009-present Yankee Environmental model TPC-3000 Total Precipitation Collector
  • Precipitation volume 1983-June 2007 Belfort Instrument Co. Universal Recording Rain Gauge, Series 5-780, sensitivity +0.05 inch (1.3 mm), recommended significant figs. 2. Gauge was encircled by wind alter-shields. The tops of the alter-shields were level with the opening of the rain gauge. Precipitation amount from each event was checked using a standard plastic rain gauge and/or a snow depth / rain gauge. July 2007-present, Geonor Precipitation Gauge Model T-200B from co-located USCRN station.


Each sample is weighed to check that the volume of sample collected is within a reasonable range of the volume of precipitation that is recorded by the precipitation gauges. Sample buckets are discarded every 3-12 months and replaced with new, clean buckets. To clean new buckets, they are rinsed 10 times with deionized water, 10 times with double deionized water, filled with double deionized water and allowed to stand overnight, rinsed again 10 times with double deionized water and filled again with double deionized water. The conductivity of the double deionized water in the bucket is checked. If it is more than the conductivity of double deionized water in a clean beaker (less than 1 umho), the process is repeated. Sample bottles are cleaned by rinsing with deionized water 7 times, filling with deionized water, allowed to stand overnight and rinsed again 4 times. A small amount of the precipitation sample is used to rinse the bottle before it is filled with the sample. Once each year a bucket is placed in the collector and retrieved before a precipitation event occurs. This bucket is returned to the lab where it is filled with double deionized water, which is bottled, preserved and analyzed as a regular sample. This is to ensure that sample-handling techniques introduce no contamination.

When analytical results are received from the Cary Institute analytical lab, data are examined and checked using two methods. First, ion balances and ionic strength are calculated using the following equations:

Ion Balance = ((ANIONS - CATIONS)/((CATIONS+ANIONS)/2))*100;
Ionic Strength = ANIONS + CATIONS;
CATIONS = caueq + mgueq + naueq + kueq + nh4ueq + hueq;
ANIONS = no3ueq + so4ueq + clueq + po4ueq;

concentrations are in mg/L and conc_H=1000*EXP(-2.3026*PH)

Ion balances and ionic strength are examined and samples are considered for reanalysis if the following criteria are met:

  • Ionic Strength (ueq) and Ion Balance (%)
  • Less than 50greater than 40
  • Between 50 and 100greater than 20
  • Greater than 100greater than 10

The quality of data is also checked by examining time series graphs of sample concentrations for each analyte. If any samples are obvious outliers, they are considered for reanalysis.

Analytical methods and Instrument notes including calibration schedule, malfunctions and repairs, new instrumentation, anecdotal information etc. are available on request.


Missing values are represented by a single decimal point.