Documentation for Measurements of Air and Snow Photochemical Species at WAIS Divide, Antarctica, Version 1

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Detailed Data Description

Atmospheric measurements were made 1 m above the snow, 10 m upwind (prevailing winds from NE) from the tent, with ambient air continuously drawn through an insulated and heated PFA (1/4 I.D.) intake line (typically 1.4 STP-Lmin-1) of 12 m for peroxides (ROOH), and of 20 m for nitric oxide (NO) and ozone (O3). All surface snow and snow pits were sampled in a 7200 m2 clean area upwind from the Polarhaven tent. The top 1 cm of the non-cohesive surface snow was collected daily while snow pits were sampled on a weekly basis at 2 cm resolution to a depth of 30 cm. Concentrations of snowflakes from the only snow precipitation observed are reported.

Format

Data are provided in Tab-delimited ASCII Text (.txt) format.

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File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/AGDC/nsidc0585_bales/ directory. Within this directory, there are five text files:

WAISchemistry_atm_NO-O3-ROOH.txt
WAISchemistry_snowpit_20081218.txt
WAISchemistry_snowpit_20081228.txt
WAISchemistry_snowpit_20090104.txt
WAISchemistry_surfacesnow.txt

Refer to Table 1 for an explanation of the content for each text file.

Table 1. File Content Description
File Name Description of Content
WAISchemistry_atm_NO-O3-ROOH.txt Atmospheric mixing ratios in pptv of nitric oxide (NO), surface ozone (O3), hydrogen peroxide (H2O2), and methyl hydroperoxide (MHP) plus the Standard Deviation (stdev) of the last two variables. Date and Time in UTC.
WAISchemistry_snowpit_20081218.txt Snow concentrations in ppbw of H2O2, formaldehyde (HCHO), nitrate (NO3), nitrite (NO2), and their corresponding Standard Deviations (stdev), measured in a 30 cm depth snowpit on 12/18/2008. Depth in cm.
WAISchemistry_snowpit_20081228.txt Snow concentrations in ppbw of H2O2, HCHO, NO3, NO2, and their corresponding Standard Deviations (stdev), measured in a 30 cm depth snowpit on 12/28/2008. Depth in cm.
WAISchemistry_snowpit_20090104.txt Snow concentrations in ppbw of H2O2, HCHO, NO3, NO2, and their corresponding Standard Deviations (stdev), measured in a 30 cm depth snowpit on 01/04/2009. Depth in cm.
WAISchemistry_surfacesnow.txt Snow concentrations in ppbw of H2O2, HCHO, NO3, NO2, and their corresponding Standard Deviations (stdev), measured daily in the top 1 cm of surface snow. Date and Time in UTC.
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File Size

The files range in size from 2 KB to 1.1 MB

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Spatial Coverage

79.467° S, 112.085° W
Sample location was 5km NW of the WAIS Divide drilling camp.

Spatial Resolution

1766 m above mean sea level (a.m.s.l.)

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Temporal Coverage

Data were collected from 10 December 2008 to 11 January 2009.

Temporal Resolution

Antarctic summer only.

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Parameter or Variable

Hydrogen Peroxides Mixing Ratios and Concentrations (H2O2)
Nitric Oxide Mixing Ratio (NO)
Ozone Mixing Ratio (O3)
Nitrate Concentrations (NO3)
Nitrite Concentrations (NO2)
Formaldehyde Concentrations (CH2O)
Methyl Hydroperoxide Mixing Ratios and Concetrations (CH3OOH)

Sample Data Record

sample data record

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Software and Tools

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Data Acquisition and Processing

Data Acquisition Methods

From 10 December 2008 to 11 January 2009, atmospheric concentrations of NO and O3 were continuously measured at WAIS Divide (local time: LT = UTC-07:30). Mixing ratios of ROOH (H2O2 and MHP) were recorded between 31 December 2008 to 7 January 2009. Snow samples were collected daily from the surface and weekly from 30 cm snow pits for chemical analysis of NO3, NO2 and H2O2 (Masclin et al 2013).

Atmospheric sampling took place 5 km NW of the WAIS Divide drilling camp (79.467° S, 112.085° W, 1766 m a.m.s.l.). All instruments were run out of a Polarhaven tent heated by a preway heater. Atmospheric measurements were made 1 m above the snow, 10 m upwind (prevailing winds from NE) from the tent, with ambient air drawn through an insulated and heated PFA (1/4 I.D.) intake line (typically 1.4 STP–L min–1) of 12 m for ROOH, and of 20 m for NO and O3. In an attempt to minimize artifacts in the atmospheric records, the two generators (3.5 and 5 KW) that provided electricity to the lab were located about 30 m downwind from the sampling lines, and all activities around the site were restricted. However, the heater exhaust was located on the top of the Polarhaven tent (Masclin et al 2013).

Atmospheric Sampling

Atmospheric Nitric Oxide (NO) measurements were taken using a modified chemiluminescence instrument. NO mixing ratios recorded at 1 Hz were aggregated to 1 min averages. The Limit of Detection (LOD), defined as 2-σ of the background count rate, was 5 pptv (Masclin et al 2013).

A two-minute background signal was monitored every 20 minutes and an automatic four minute calibration was performed every two hours by addition of a 2 ppmv NO standard. Due to late delivery of this NO gas standard to the site, calibration was only run during the last three days of the campaign. The instrument sensitivity remained fairly constant over the three days, with an average over 16 calibrations of 7.10 ± 0.18 Hzpptv –1, similar to the preseason value of 7.00 Hzpptv –1 determined in the lab. We therefore used the three-day average value of these calibrations to process the overall data set. NO spikes related to pollution from generators and heater exhaust were removed using a moving standard deviation filter with a maximum standard deviation of 30 (1.5 times the interquartile range of the data set). This led to the removal of 25 percent from the raw NO record (Masclin et al 2013).

Tropospheric ozone (O3) was monitored at 1 min resolution using a 2B Technologies (Golden, Colorado) O3 Monitor, Model 205, with a 1 ppbv LOD. (Masclin et al 2013).

Atmospheric Hydroperoxides (ROOH) were measured at 10 minute resolutions based on continuous scrubbing of sample air followed by separation in an HPLC column and fluorescence detection, described in detail by Frey et al (2005) and Frey et al (2009a). The detector was calibrated 1–2 times per day with H2O2 solution and MHP standards synthesized in our lab following the protocol described by Frey et al (2009a). The LOD, 2-σ of the baseline, were 87 pptv for H2O2 and 167pptv for MHP. Unexpected variations of the coil-scrubber temperatures may have caused higher LOD than those reported by Frey et al (2005) and Frey et al (2009a).

Snow Sampling

All surface snow and snow pits were sampled in a 7200 m2 clean area upwind from the Polarhaven tent. The top 1 cm of the non-cohesive surface snow, referred to as the skin layer (Frey et al (2009b) and (Erbland et al (2013), was collected daily with a 10 mL glass test tube to assess temporal changes in snow chemistry. Twice during the campaign, the skin layer was sampled simultaneously at five different spots inside the clean area to assess possible local spatial variability of NO3, NO2, and H2O2(Masclin et al 2013).

Weekly snow pits were sampled at 2 cm resolution to a depth of 30 cm, covering the snowpack zone where 85 percent of NO3 photolysis is expected to occur (France 2011). Snowflakes were collected on aluminum foil during the only snow precipitation event observed during the campaign, on 12 December 2008 (Masclin et al 2013).

All snow samples were collected in 100 mL SCHOTT bottles and kept frozen during storage and transport until analysis 14 months later. The analysis involved melting the snow one hour before injecting the sample into a self-built Continuous Flow Analysis (CFA) system as described by Frey et al (2006). The LOD, defined as 3σ of the baseline, was 0.4 ppbw for NO3, NO2, and H2O2. Only values above LOD were used for further calculations. Some loss of NO2 in the samples may have occurred between the time of collection and analysis, as Takenaka and Bandow (2007) and O'Driscoll et al.(2012) showed that NO2 may be oxidized during freezing and storage(Masclin et al 2013).

More details on database development (experimental method, data processing) and discussion of the results are published in Masclin et al 2013.

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Data Processing Steps

Atmospheric Concentration

The average ± 1 σ (median) of NO over the campaign was 19 ± 31 (10) pptv. Refer to Table 2. Some noise remained in the NO data set after filtering; however, the 4 h running median shows very little change in the overall trend of the data due to filtering, with the median value after filtering similar to that of the raw dataset (6 pptv). Refer to Figure 1a. One-minute data did not exhibit any clear diel cycle (Figure 1), but 1 h binned data centered on each hour for the measurement period revealed a diel cycle that can be interpreted with the variations of the average solar elevation angle. Refer to Figure 2b. NO mixing ratios increased at 07:00–08:00 LT with a maximum rise of 36 percent from the daily median of 10 pptv. A decrease was observed afterwards and followed by a second increase of 20 percent above the median value at 19:00 LT. These peaks in NO occurred as solar elevation angle increased and decreased, with lower values of NO at the maxima and minima of solar elevation angle (Masclin et al 2013).

table 1

fig1
Figure 1. Atmospheric mixing ratios of NO after filtering and O3 (1 min averages), and of H2O2 and MHP (10-minute averages) during austral summer 2008–2009 at WAIS Divide. The 4 h running median of NO is also shown (red symbols).

fig2
Figure 2. Diel variation of: (a) average Solar Elevation Angle (SEA) and wind speed; (b) median NO (left axis) and O3 (right axis), and (c) median H2O2 and MHP. Symbols and lines are 1 h binned values centered on each hour; shaded area and error bars indicate the range between the first and third quartiles; local time is UTC–07:30.

Average ± 1σ (median) mixing ratios of O3 at WAIS Divide were 14 ± 4 (13) ppbv. Refer to Table 2. The mean is two thirds of the 20 ± 2 ppbv average mixing ratio observed at Byrd Station in summer 2002, but is in the range of values from previous measurements between 79.06° S and 85.00° S above the WAIS (Frey et al. 2005 ). Refer to Figure 3. Two events of elevated O3 levels were recorded between 24 and 25 December, and between 27 and 29 December, with concentrations in the range of 20 to 30 ppbv. Refer to Figure 1. Concentrations above 25 ppbv were only observed for winds blowing from ENE to SWS. This 135° sector represents 67 percent of all the wind directions observed during the field campaign. Refer to Figure 4. The hourly binned O3 data (Figure 2b) show a small diel cycle in phase with solar elevation angle and wind speed. The mixing ratios rose by 5 percent of the median value (13 ppbv) in the morning, reaching a maximum at 14:00 LT and dropping thereafter in the afternoon (Masclin et al 2013).

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Figure 3. Report of some previous Antarctic measurements of atmospheric NO, surface O3, H2O2, plus NO3 in surface snow. Data from Frey et al. (2013)Preunkert et al. (2012)Frey et al. (2009a)Legrand et al. (2009)Frey et al. (2005)Dibb et al. (2004)Davis et al. (2004)Rothlisberger et al. (2000)Jacobi et al. (2000)Jones et al. (1999),Mulvaney et al. (1998)Jefferson et al. (1998), NOAA/GMD, and AWI (http://ds.data.jma.go.jp/gmd/wdcgg/).
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Figure 4. The windrose for WAIS Divide for period of 10 December 2008 to 5 January 2009 and O3 concentrations from each direction for the same period.

Concentrations of H2O2 and MHP were measured between 31 December 2008 and 5 January 2009. Refer to Figure 1. Averages ± 1 σ (medians) were 743 ± 362 (695) and 519 ± 238 (464) pptv for H2O2 and MHP, respectively. Our records are closer to values observed at West Antarctic sites below 1500 m a.m.s.l. and higher than measurements made in the surrounding area. Refer to Fig. 3. With mixing ratios of H2O2 that were twice those observed at Byrd station in late November 2002 (Frey et al. 2005 )Refer to Table 2. Average ± 1 σ (range) of the MHP : (H2O2 ± MHP) ratios were 0.42 ± 0.10 (0.12–0.76). These values are in the range of those previously recorded over WAIS (Frey et al. 2005 ). Binned values suggest, for both H2O2 and MHP, a diel cycle with respective maximum 44 and 37 percent above their medians (695 and 464 pptv) observed in the morning. Refer to Figure 2c(Masclin et al 2013).

Snow Concentration

Average ± 1 σ (median) concentrations of NO2, NO3, and H2O2 in the skin layer at WAIS Divide were 0.6 ± 0.4 (0.5), 137 ± 37 (142) and 238 ± 37 (238) ppbw, respectively.Refer to Table 2. Daily concentrations of NO2 in the skin layer showed a decrease of 30 pptw per day ( R 2 = 0.36) over the campaign. Refer to Figure 5. This decrease represents a rate of 5 percent per day of the average concentration of NO2 measured in all of the snow surface samples. Unlike NO2, NO3, and H2O2 exhibited some variation but no trend was observed for these species (Masclin et al 2013).

The coefficients of variation of concentrations of NO2, NO3, and H2O2 in the skin layer are 49 percent, 26 percent and 17 percent, respectively. The coefficients of variation for samples collected simultaneously on 1 and 8 January 2009 (Figure 5 ) are 17 percent, 31 percent and 7 percent for NO2, NO3,, and H2O2 respectively. The similar coefficients of variation for NO3 concentrations in snow imply that spatial variability contributes significantly to the overall variability and thus a temporal trend may be difficult to detect. For NO2 and H2O2, the coefficients of temporal variability (49 percent and 17 percent, respectively) are more than double those calculated from spatial variability (17 percent and 7 percent, respectively). The variations of daily concentrations of NO2 and H2O2 in near-surface snow may then be interpreted as temporal trends. Concentrations of H2O2 in the top 5–15 cm of the profile (Figure 6 ) may also indicate a temporal trend; seasonal increase in concentrations measured over this period was apparent not only in the top 5 cm of snow, but also down to at least 15 cm. Although there was no new snow accumulation during this period, there was wind redistribution and atmosphere–snow exchange of H2O2 and other atmospheric gas species, or nighttime deposition of fog (Masclin et al 2013).

fig5
Figure 5. Surface-snow concentrations and snow concentrations from the 12 December 2008 precipitation of (a) NO3 , (b)NO2(c) H2O2. The shaded area in (b) represents the NO2 LOD.

fig6
Figure 6. Snow concentrations of (a)NO3(b)NO2 and (c) H2O2 measured in the 30 cm-depth snow pits dug on 18 December 2008 (red squares), 28 December 2008 (blue triangles) and 04 January 2009 (green crosses). The shaded area in (b) represents the NO2– LOD.

The 30 cm deep profiles of NO2, NO3, and H2O2 illustrated in Figure 6 represent concentration changes of these species in snow over the last six months of 2008, based on local mean annual snow accumulation rate of 0.20 m weq yr -1 (Banta et al. 2008) and an average snow density of 0.37. Total concentrations of NO3– in the snow column dropped by about 19 percent between the first and last snow-pit samplings. NO3 concentrations decrease by 94-188 ppbw over the top 5 cm of snow, reaching approximately 30 ppbw below. Total NO2 stored in the 30 cm column decreased by about 65 percent across the three snow-pit samplings. Unlike NO2 and NO3, total concentrations of H2O2 in the top 30 cm of snowpack doubled over the 18 days of sampling. A 233-298 ppbw decrease of H2O2 concentrations in the first 10 cm of each snow pit was generally observed.

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References and Related Publications

Contacts and Acknowledgments

Roger Bales
University of California, Merced
Sierra Nevada Research Institute
5200 North Lake Road
Merced, California 59343

Sylvain Masclin
University of California, Merced
Sierra Nevada Research Institute
5200 North Lake Road
Merced, California 59343

Acknowledgments: 

This research was supported by NSF OPP Grant Number 0636929.

Document Information

DOCUMENT CREATION DATE

March 2014