Latest revision: 15 April 2020 by Seth Lyman

This is a dataset of elemental and oxidized mercury in the ambient atmosphere at latitude 39.912799 and longitude -105.188587.  This is the locations of the Rocky Flats North air quality monitoring station, operated by the Colorado Department of Public Health and Environment.  We collected these measurements using a dual-channel atmospheric mercury speciation instrument.  The instrument is described in detail in the following paper, which has been submitted for publication in Environmental Science and Technology:
Lyman S.N., Gratz L.E., Dunham-Cheatham S.M., Gustin, M.S., and Luippold, A., 2020. Improvements to the accuracy of atmospheric oxidized mercury measurements.  Submitted to Environmental Science and Technology.

Briefly, the instrument pulled air through a teflon-coated elutriator and particle impactor and then through a 6 m 1/4" PFA teflon tube that was heated to 120 degrees C. The air was then pulled either through a pyrolyzer that was heated to 650 degrees C, or through a series of two cation-exchange membranes.  The pyrolyzer converted all mercury to elemental mercury, while the cation-exchange membranes captured oxidized mercury and only allowed elemental mercury to pass through.  After passing through the membranes or pyrolyzer, the air was sampled for elemental mercury concentration by a Tekran 2537B analyzer.  The difference between total mercury sampled through the pyrolyzer stream and elemental mercury sampled through the membrane stream was oxidized mercury.  We measured total mercury for five minutes, then elemental mercury for five minutes, and then back again to total mercury.  We calculated oxidized mercury for each ten-minute measurement set.  We then averaged the measurements together  for each one-hour period.

Information about calibrations, instrument performance, etc., are available in the publication.

the dataset contains three columns.  The following is a description of each column:

Date and Time (MST)--this is the date and time, in Mountain Standard Time (local standard time) each measurement in the subsequent columns.  The row with the time 7/24/2018 13:00 gives data averaged from 13:00 to 13:59.

Elemental mercury (ng/m3)--this is the concentration of gas-phase elemental mercury in the ambient atmosphere.

Oxidized mercury (pg/m3)--this is the concentration of total oxidized mercury in the ambient atmosphere.  Since the measurement system calculates oxidized mercury as the difference between elemental and total mercury, sometimes oxidized mercury concentrations are less than zero.  The detection limit for oxidized mercury during this deployment is about 40 pg/m3.  Data below the detection limit are shown.

Empty cells (null values) indicate that no data were available for that period, due either to instrument calibration periods or instrument malfunction.

In version 2 of this dataset, we adjusted elemental and oxidized mercury values down by an average of 12%.  The process for these adjustments is described in detail in the paper.  Briefly, the internal calibration system of the Tekran 2537B mercury analyzer used to collect these measurements behaved somewhat erratically during the field deployment.  The deployment included measurements from another Tekran mercury analyzer that had a more stable calibration response.  Since both instruments sampled the same air, we corrected the mercury values generated in in this dataset to account for the different calibration response relative to the more stable instrument.