1. Dataset Title: Elemental and oxidized mercury in the atmosphere at Horsepool, Utah, January-July 2019 2. Name and contact information of PI: a. Name: Seth Lyman b. Institution: Bingham Research Center, Utah State University c. Address: 320 N. Aggie Blvd., Vernal, Utah, U.S.A., 84078 d. Email: seth.lyman@usu.edu e. ORCiD ID: 0000-0001-8493-9522 3. Funding source (Agency, Grant Number) if applicable: U.S. National Science Foundation, award number 1700722 4. Project summary, description or abstract: This is a dataset of elemental and oxidized mercury in the ambient atmosphere at latitude 40.143° N and longitude 109.469° W. This is the location of the Horsepool monitoring station in the Uinta Basin, Utah. We collected these measurements using a dual-channel atmospheric mercury speciation instrument, which is described by Lyman, S. N., Gratz, L. E., Dunham-Cheatham, S. M., Gustin, M. S., & Luippold, A. (2020). Improvements to the accuracy of atmospheric oxidized mercury measurements. Environmental Science & Technology, 54(21), 13379-13388. 5. Brief description of collection and processing of data: 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. Non-mercury data were collected as described in https://www.usu.edu/binghamresearch/files/reports/UBAQR-2019-AnnualReport_v3.pdf 6. Description of file: Horsepool_Hg_2019.csv contains hourly average data for each of the parameters described below in comma separated values format. 7. Descriptions of parameters/variables: a. Temporal (beginning and end dates of data collection): January through July 2019. c. Description of data in each column of the data file: i. Date and Time (MST)--this is the date and time, in Mountain Standard Time (local standard time) each measurement in the subsequent columns. 2019 Jan 17 16:00 indicates that the measurements for that row were averaged from 16:00 to 16:59. ii. Hg_0--this is the concentration of gas-phase elemental mercury in the ambient atmosphere in ng/m3. iii. Hg_II--this is the concentration of total oxidized mercury in the ambient atmosphere in pg/m3. 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 15 pg/m3. Data below the detection limit are retained in the dataset. iv. RH_Avg--ambient relative humidity in percent. v. AT_C--ambient air temperature in Celcius. vi. WS_ms_Avg--wind speed in m/s, measured at 10 m above ground level. vii. WindDir--wind direction in degrees, measured at 10 m above ground level. viii. O3_Avg--ozone in ppb ix. CO_Avg--carbon monoxide in ppb x. NO_Avg--nitrogen oxide in ppb. The NO instrument's sensitivity was about 1 ppb, and excursions below 0 ppb were common. Data below the sensitivity level are retained in the dataset. xi. NO2_Avg--nitrogen dioxide in ppb. The caveat about sensitivity for NO also applies to NO2 xii. NOx_Avg--NOx in ppb. NOx is the sum of NO and NO2. xiii. NOy_Avg--NOy in ppb. NOy is the sum of all reactive nitrogen. The caveat about sensitivity for NO also applies to NOy. xiv. PM25CONC--particles with an aerodynamic diameter smaller than 2.5 microns in micrograms per cubic meter. xv. methane--methane in ppm xvi. TNMHC--total non-methane hydrocarbons in ppb of carbon atoms. xvii. BP-mBar_Avg--barometric pressure in mbar xviii. CNR_SW_top_Avg--total incoming shortwave radiation xix. snow depth--24-hour average snow depth at the study site d. Location: Horsepool monitoring station, latitude 40.143° N and longitude 109.469° W e. Symbol used for missing data: Empty cells (null values) indicate that no data were available for that period, due either to instrument calibration periods or instrument malfunction. 8. Special software required to use data: none. 9. Publications that cite or use this data: An analysis of these measuremements has been submitted for publication: Lyman, S. N., Elgiar, T., Sexauer-Gustin, M., Dunham-Cheatham, S., & Zhang, L. (2021). Evidence against reapid mercury oxidation in photochemical smog. Nature Geoscience, submitted. 10. Quality assurance and quality control: See Lyman, S. N., Gratz, L. E., Dunham-Cheatham, S. M., Gustin, M. S., & Luippold, A. (2020). Improvements to the accuracy of atmospheric oxidized mercury measurements. Environmental Science & Technology, 54(21), 13379-13388. and the submitted publication (section 9)