urn:x-wmo:md:org.aoncadis.www::3a123cac-d496-11de-892a-00c0f03d5b7c 3a123cac-d496-11de-892a-00c0f03d5b7c William Simpson University of Alaska, Fairbanks wrsimpson@alaska.edu https://orcid.org/0000-0002-8596-7290 Donald Perovich Donald.K.Perovich@erdc.dren.mil https://orcid.org/0000-0002-0576-0864 Patricia Matrai Bigelow Laboratory for Ocean Sciences pmatrai@bigelow.org https://orcid.org/0000-0003-1656-5519 Paul Shepson Purdue University pshepson@purdue.edu https://orcid.org/0000-0002-1726-3291 Francisco Chavez Monterey Bay Aquarium Research Institute chfr@mbari.org https://orcid.org/0000-0002-0691-292X 2009-11-18 eng

Collaborators from five institutions worked to build and deploy an Arctic Ocean network of rugged and autonomous buoys (named "O-Buoys"), capable of observing three key atmospheric chemical species, bromine monoxide-BrO, ozone-O3, and carbon dioxide-CO2 through 2017 (with each O-Buoy being operational for up to 2 years). O3 and CO2 are two of the most important greenhouse gases that have, as yet, poorly understood behavior in the Arctic. BrO is a reaction intermediate that is involved in the extraordinary ozone and mercury atmospheric depletion that occurs during polar springtime, both of which have strong consequences for human and ecosystem health in the Arctic region. These buoys are immersed through the sea ice into the ocean surface, thereby providing a constant temperature (-1.7 degrees C) environment for sensor stability. The original O-Buoy project funded by NSF included design and testing of the O-Buoy. In the current project, 11 new O-Buoys were constructed and deployed (sometimes twice) along with the four already built. As a pilot project, two of the new O-Buoys included seawater sensors for CO2, oxygen, pH, fluorescence, backscatter, temperature and salinity in addition to the atmospheric O3, BrO, and CO2 sensors. Throughout the project, data from each O-Buoy were subject to QA/QC protocols by automated processing initially, with preliminary data available on a regular basis on the NSF Arctic Data Center site. All final data and metadata are ultimately archived on Arctic Data after final analysis at the end of each deployment (please search under O-Buoy, Matrai and/or Simpson). This network of O-Buoys, coordinated and clustered with other buoys in ice based observatories, enabled the scientific community to first observe and, next, better understand the impact of Arctic surface change on atmospheric composition and chemistry. Outreach was done to many K-silver organizations. Video footage from deployments/recoveries and interviews with colleagues and native Arctic people were contributed to the http://www.arcticstories.net site, the Beaufort Gyre Exploration Project (http://www.whoi.edu/beaufortgyre/expeditions), the Nansen and Amundsen Basins Observational System (NABOS-II, http://research.iarc.uaf.edu/NABOS2/), and the O-Buoy web site (http://www.o-buoy.org/).

AON This work is licensed under the Creative Commons Attribution 4.0 International License.To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Beaufort Sea region, representing O-Buoy 1, 2, 7, 8, 10, 11, 12, 13, and 14. -170 -130 82 74 East Siberian Sea region, representing O-Buoys 8, 9, 15. 130 140 87 82 North Pole region, representing O-Buoy 4 and 6. -160 -20 90 88 Hudson Bay region, representing O-Buoy 3. -94.0997 -88.2997 60.2000 58.7997 2007-09-11 00:00:00 2016-11-10 00:00:00 William Simpson University of Alaska, Fairbanks wrsimpson@alaska.edu https://orcid.org/0000-0002-8596-7290 Donald Perovich Donald.K.Perovich@erdc.dren.mil https://orcid.org/0000-0002-0576-0864 Patricia Matrai Bigelow Laboratory for Ocean Sciences pmatrai@bigelow.org https://orcid.org/0000-0003-1656-5519 Paul Shepson Purdue University pshepson@purdue.edu https://orcid.org/0000-0002-1726-3291 Francisco Chavez Monterey Bay Aquarium Research Institute chfr@mbari.org https://orcid.org/0000-0002-0691-292X

Ambient surface-level ozone mole fractions were determined using customized 2B Technologies model 205 dual-beam O3 monitors (https://www.twobtech.com/index.html). These instruments operate on the principle of the Beer-Lambert Law. Briefly, ambient air is sampled at the O-Buoy mast at a height of approximately 1.5 m above sea level. Air travels through a stainless-steel encased PFA Teflon filter holder that contains a Teflon filter (90 mm, PTFE, ZITEX). Sample air is drawn through approximately 4 meters of PFA Teflon tubing into the 2B Technologies model 205 instrument (O-Buoys 1-4, 6-8 utilized a 0.16'' inner dimeter tubing, O-Buoy 5 used a 1/8'' inner diameter tubing, and O-Buoys 9-15 utilized a ¼” inner dimeter tubing. Tubing diameter was not found to significantly affect accuracy of results). Inside the 2B instrument, the air is then divided equally into a “scrubbed path” and a “sample path”. In the scrubbed path, ozone is removed from the sample using a hopcalite-based ozone scrubber. The air in both pathways is then pumped into two separate 15-cm long absorption cells. Both cells are illuminated by photons of wavelength 254 nm (near the wavelength of maximum absorption for ozone), emitted from a low-pressure mercury lamp. In the sample path, ozone attenuates this light by absorbing these photons at an amount proportional to its concentration in the air (i.e., transmitted irradiation). Minimal absorption should occur in the scrubbed path (i.e., total irradiation), and only by other species that also absorb at 254nm thath are not removed by the scrubber; these species are presumably present at equal concentrations in both paths. The light passing through both cells is detected by photodiodes (outfitted with interference filters, centered at 254 nm), producing electrical signals that are compared and converted to mole fractions by the instrument software. After passing out of the absorption cell, sample air is exhausted out of the buoy. Customizations to the commercially available instruments include the use of rotary vane pumps more conducive to operating in cold-weather conditions (Thomas G 12/02 EB rotary vane pumps), one backup pump, a lamp heater to maintain the light source at constant temperature, and modified firmware to control the instrument remotely. The 2B instruments installed on O-Buoys 12-15 were fitted with 12V DC-DC converters to ensure that the 2Bs were consistently powered at a nominal 12V. The major sources of chemical interference from this method comes from other molecules that absorb significantly at a wavelength of 254-nm, primarily including polyaromatic hydrocarbons (PAHs) and mercury. However, relative concentrations of both species in the Arctic are not large enough to influence measurements beyond the manufacturer specified level of precision (1 nmol mol-1). The instrument has a manufacturer specified limit of detection of 2 nmol mol-1, and individual measurement uncertainty was calculated to range from 2.1 – 3.5 nmol mol-1 (“ppbv”) using our specific configuration. Blank measurements are performed everyday by remotely altering the instrument flow path such that the sample air is scrubbed of ozone (i.e., both flow paths contain no ozone). Further information of data quality and treatment can be found in the ozone instrument readme file. Additional detail can be found in Knepp et al. (2010), Halfacre et al. (2014), and Halfacre (2016).

Halfacre, J. W.: Studies of Arctic Tropospheric Ozone Depletion Events Through Buoy-Borne Observations and Laboratory Studies, Ph.D., Purdue University, United States -- Indiana, 2016. Halfacre, J. W., Knepp, T. N., Shepson, P. B., Thompson, C. R., Pratt, K. A., Li, B., Peterson, P. K., Walsh, S. J., Simpson, W. R., Matrai, P. A., Bottenheim, J. W., Netcheva, S., Perovich, D. K. and Richter, A.: Temporal and spatial characteristics of ozone depletion events from measurements in the Arctic, Atmos. Chem. Phys., 14(10), 4875–4894, doi:10.5194/acp-14-4875-2014, 2014. Knepp, T. N., Bottenheim, J., Carlsen, M., Carlson, D., Donohoue, D., Friederich, G., Matrai, P. A., Netcheva, S., Perovich, D. K., Santini, R., Shepson, P. B., Simpson, W., Valentic, T., Williams, C. and Wyss, P. J.: Development of an autonomous sea ice tethered buoy for the study of ocean-atmosphere-sea ice-snow pack interactions: the O-buoy, Atmos. Meas. Tech., 3(1), 249–261, doi:10.5194/amt-3-249-2010, 2010.

Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) was employed by the O-Buoy as a means of detecting BrO, though it is additionally capable of detecting other trace gases (e.g., IO, O3, NO2, HONO). The MAX-DOAS instrument observes scattered sunlight within a spectral region where a molecule of interest absorbs as a function of the elevation angle at which a telescope receives light (90, 20, 10, 5, 2, and 1o). The spectra obtained include the impacts of all of the chemical absorbers in a slanted column and are thus retrievals result in a quantity called slant column densities (SCDs; units of molecules cm-2). However, observations at all elevation angles have absorption features originating from gases in the free troposphere, and stratosphere. To remove these possible interferences, the SCDs from the 90o elevation angle measurement, which sees minimal tropospheric / boundary layer absorption, is used as a reference (blank) that can is subtracted from SCDs at lower elevation angles. These differential slant column densities (dSCDs) have enhanced sensitivity to boundary layer gases and can be inverted to retrieve vertical profile information on molecules of interest. Separation of gases with overlapping absorption bands is achieved using QDOAS software (Fayt et al., 2011) to fit a linear combination of possible absorbing spectra at each elevation angle. A common wavelength interval, typically from 337nm to 364nm, was used for BrO, NO2, O3, and O4 spectral fitting. Molecular absorbers were not allowed to shift with respect to the wavelength scale, and the rotational Raman scattering, aka “Ring” spectrum (Grainger and Ring, 1962) was constrained to be within 0.1nm of the reference spectrum, but was typically closer to zero shift. To account for the "tilt effect", the spectrum was allowed to shift with respect to the reference (Lampel et al., 2017b; Rozanov et al., 2011); these shifts were significantly smaller than one pixel. For the Avantes spectrometers (later O-Buoys), no intensity offset was allowed, but for the Ocean Optics (early O-Buoys), a constant offset was fitted to account for instrumental stray light, which was found to be significantly larger for the Ocean-Optics-based instruments. The BrO absorption cross section was from at 243K. The NO2 cross section was from Voigt et al. (2002) at 260K. The O4 absorption cross section was from Thalman and Volkamer (2013) at 273K. Additionally, the difference between the 253K and 293K O4 cross sections was fitted to account for the temperature-dependent O4 absorption shape. The ozone cross section was from Serdyuchenko et al. (2014) at 263K, and the temperature difference between ozone cross sections at 243K and 283K was used to account for temperature dependent absorption shape. The rotational Raman scattering (Ring) pseudo-absorber spectrum was calculated in DOASIS (Kraus, 2006) at 273K, and a Ring effect temperature dependence was calculated as the difference between 273K and 243K, as found in Lampel et al. (2017a). The result of the spectral fitting is a “Level-2” data file, which contains slant column abundances of gases as a function of elevation angle. The L2 data sets also contain quality control and housekeeping parameters. The subsequent inversion of dSCDs to obtain vertical profile information concerning BrO is a two-step procedure. The first step is to model the aerosol particle extinction vertical profile using the well-known vertical profile of the O2 collision dimer, O4, which has a dSCD highly dependent on atmospheric visibility and light scattering (Greenblatt et al., 1990; Hönninger et al., 2004). Based on the observed dSCD values of O4, a radiative transfer model (Rozanov et al., 2005) can be used to estimate particle extinction profiles based on viewing angles and aerosol light scattering properties. Once this profile is obtained, it is input into a second radiative-transfer simulation is used to invert the observed BrO dSCDs to a BrO concentration profile (Frieß et al., 2011; Peterson et al., 2015). The vertical profile of BrO is varied to give the best fit by optimal estimation. The result of this inversion is a “Level-3” data set, which includes information about surface-level BrO and the lower-tropospheric partial vertical column density (LT-VCD) of BrO. See the metadata associated with the L3 data files for details on data in those files. The MAX-DOAS hardware is closely related to the systems described by Carlson et al. (2010) and Knepp et al. (2010). It consists of two major components: a scanhead telescope and the computer/spectrometer unit. The scanhead telescope, which takes in the scattered light, is mounted on the very top of the O-Buoy mast, and transfers this light signal to the computer/spectrometer unit, located in the O-Buoy hull, by a fiber optic connection. The computer/spectrometer unit consists of a low-power single-board computer (Technologic Systems TS-7260), a stepper motor driver (Stepperboard BC2D20), interface electronics, and a miniature spectrometer (Ocean Optics or Avantes, depending upon O-Buoy). Additionally, a tilt-sensing system was included such that the tilt of the O-Buoy (and thus the scanhead) could be both measured using a digital inclinometer (Smart Tool Technologies ISU-S), and corrected (up to 20o) to maintain accurate alignment of the viewing direction with the true horizon. Later O-Buoys used a micro-electro-mechanical system (MEMS) tiltmeter (SignalQuest SQ-SI-360DA-3.3R-HMP-HP-IND-S) mounted directly onto the moving telescope (moved from the scanhead housing in the original design) such that direct measurement of the elevation angle is possible. For more details on the principles of MAX-DOAS, as well as the methods used for processing the data, the reader is referred to Hönninger et al. (2004), Carlson et al. (2010), and Frieß et al. (2011), Peterson et al. (2016), and Simpson et al. (2017).

Carlson, D., Donohoue, D., Platt, U. and Simpson, W. R.: A low power automated MAX-DOAS instrument for the Arctic and other remote unmanned locations, Atmos. Meas. Tech., 3(2), 429–439, doi:10.5194/amt-3-429-2010, 2010. Fayt, C., De Smedt, I., Letocart, V., Merlaud, A., Pinardi, G., Van Roozendael, M. and Roozendael, M.: QDOAS Software user manual, Belgian Institute for Space Aeronomy: Brussels, Belgium, 2011. Fleischmann, O. C., Hartmann, M., Burrows, J. P. and Orphal, J.: New ultraviolet absorption cross-sections of BrO at atmospheric temperatures measured by time-windowing Fourier transform spectroscopy, Journal of Photochemistry and Photobiology A: Chemistry, 168(1), 117–132, doi:10.1016/j.jphotochem.2004.03.026, 2004. Frieß, U., Sihler, H., Sander, R., Pöhler, D., Yilmaz, S. and Platt, U.: The vertical distribution of BrO and aerosols in the Arctic: Measurements by active and passive differential optical absorption spectroscopy, Journal of Geophysical Research, 116, doi:10.1029/2011JD015938, 2011. Grainger, J. F. and Ring, J.: Anomalous Fraunhofer Line Profiles, Nature, 193(4817), 762, doi:10.1038/193762a0, 1962. Greenblatt, G. D., Orlando, J. J., Burkholder, J. B. and Ravishankara, A. R.: Absorption measurements of oxygen between 330 and 1140 nm, J. Geophys. Res., 95(D11), 18577–18582, doi:10.1029/JD095iD11p18577, 1990. Hönninger, G., von Friedeburg, C. and Platt, U.: Multi axis differential optical absorption spectroscopy (MAX-DOAS), Atmos. Chem. Phys., 4(1), 231–254, doi:10.5194/acp-4-231-2004, 2004. Knepp, T. N., Bottenheim, J., Carlsen, M., Carlson, D., Donohoue, D., Friederich, G., Matrai, P. A., Netcheva, S., Perovich, D. K., Santini, R., Shepson, P. B., Simpson, W., Valentic, T., Williams, C. and Wyss, P. J.: Development of an autonomous sea ice tethered buoy for the study of ocean-atmosphere-sea ice-snow pack interactions: the O-buoy, Atmos. Meas. Tech., 3(1), 249–261, doi:10.5194/amt-3-249-2010, 2010. Kraus, S.: DOASIS a framework design for DOAS, PhD Thesis, Technische Informatik, Univ.\ Mannheim., 2006. Lampel, J., Pöhler, D., Polyansky, O. L., Kyuberis, A. A., Zobov, N. F., Tennyson, J., Lodi, L., Frieß, U., Wang, Y., Beirle, S., Platt, U. and Wagner, T.: Detection of water vapour absorption around 363 nm in measured atmospheric absorption spectra and its effect on DOAS evaluations, Atmos. Chem. Phys., 17(2), 1271–1295, doi:10.5194/acp-17-1271-2017, 2017a. Lampel, J., Wang, Y., Hilboll, A., Beirle, S., Sihler, H., Puķīte, J., Platt, U. and Wagner, T.: The tilt effect in DOAS observations, Atmospheric Measurement Techniques; Katlenburg-Lindau, 10(12), 4819–4831, doi:http://dx.doi.org/10.5194/amt-10-4819-2017, 2017b. Peterson, P. K.: Examining the role of sea ice and meteorology in Arctic boundary layer halogen chemistry, Dissertation, University of Alaska Fairbanks, Fairbanks, AK., 2015. Peterson, P. K., Simpson, W. R. and Nghiem, S. V.: Variability of bromine monoxide at Barrow, Alaska, over four halogen activation (March–May) seasons and at two on-ice locations, J. Geophys. Res. Atmos., 121(3), 2015JD024094, doi:10.1002/2015JD024094, 2016. Rozanov, A., Bovensmann, H., Bracher, A., Hrechanyy, S., Rozanov, V., Sinnhuber, M., Stroh, F. and Burrows, J. P.: NO2 and BrO vertical profile retrieval from SCIAMACHY limb measurements: Sensitivity studies, Advances in Space Research, 36(5), 846–854, doi:10.1016/j.asr.2005.03.013, 2005. Rozanov, A., Kühl, S., Doicu, A., McLinden, C., Puķīte, J., Bovensmann, H., Burrows, J. P., Deutschmann, T., Dorf, M., Goutail, F., Grunow, K., Hendrick, F., von Hobe, M., Hrechanyy, S., Lichtenberg, G., Pfeilsticker, K., Pommereau, J. P., Van Roozendael, M., Stroh, F. and Wagner, T.: BrO vertical distributions from SCIAMACHY limb measurements: comparison of algorithms and retrieval results, Atmos. Meas. Tech., 4(7), 1319–1359, doi:10.5194/amt-4-1319-2011, 2011. Serdyuchenko, A., Gorshelev, V., Weber, M., Chehade, W. and Burrows, J. P.: High spectral resolution ozone absorption cross-sections – Part 2: Temperature dependence, Atmos. Meas. Tech., 7(2), 625–636, doi:10.5194/amt-7-625-2014, 2014. Simpson, W. R., Peterson, P. K., Frieß, U., Sihler, H., Lampel, J., Platt, U., Moore, C., Pratt, K., Shepson, P., Halfacre, J. and Nghiem, S. V.: Horizontal and vertical structure of reactive bromine events probed by bromine monoxide MAX-DOAS, Atmos. Chem. Phys., 17(15), 9291–9309, doi:10.5194/acp-17-9291-2017, 2017. Thalman, R. and Volkamer, R.: Temperature dependent absorption cross-sections of O2–O2 collision pairs between 340 and 630 nm and at atmospherically relevant pressure, Phys. Chem. Chem. Phys., 15(37), 15371–15381, doi:10.1039/C3CP50968K, 2013. Voigt, S., Orphal, J. and Burrows, J. P.: The temperature and pressure dependence of the absorption cross-sections of NO2 in the 250–800 nm region measured by Fourier-transform spectroscopy, Journal of Photochemistry and Photobiology A: Chemistry, 149(1), 1–7, doi:10.1016/S1010-6030(01)00650-5, 2002.

An autonomous CO2 sensor was built around the LI-COR 820 IR instrument, a single path, dual wavelength, nondispersive infrared gas analyzer that allows measurement of absolute concentrations of CO2 in air. This instrument was adapted for buoy deployment as part of the TAO/TOGA buoy array in the equatorial Pacific and for numerous coastal buoys and drifters where the primary focus was the measurement of sea surface pCO2 (Friederich et al., 1995, 2008); see http: //www.pmel.noaa.gov/co2/moorings/. The precision of the deployed system was about 0.1 ppm and the accuracy was estimated to be 0.2 ppm (sufficient to determine any significant change from the seasonal range: 360–400 ppm) due to uncertainties in the standard gases as well as residual errors in the temperature and pressure corrections. The CO2 system was controlled by a low power controller (ONSET TT8v2) equipped with a set of custom made interface boards that scheduled the analyzer, pumps, and valves, collected and formatted the data, and stored all information in flash memory before passing it on to the supervisory computer for transmission. A sampling frequency of 8 measurements per day was selected. A complete sampling cycle took 6 min and had a mean power consumption of 3.5 W. The standby power consumption was less than 0.04 W. Power requirements were kept low by operating the infrared analyzer at ambient temperature without stabilization. Temperature of the measurement cell was monitored at all phases of the sample cycle and data were corrected to a common temperature using laboratory and field derived calibrations. Another factor that kept power consumption low was the choice of gas switching and distribution valves (ASCO Series AM33, after 2011 Pneumadyne series S15MML) that were magnetically latching and only required a 100 ms pulse to change position. Gas aspiration and circulation were achieved with a small diaphragm pump (KNF Neuberger UNMP015M, after 2011 TCS Micropump D220S) operated at reduced voltage with additional flow restriction to limit gas flows to about 100 mL min−1. Prior to entering the infrared analyzer all gases were dried and filtered through 0.22 micron hydrophobic filters. Drying was accomplished in sequential sections of Nafion (Permapure) tubing embedded in molecular sieve 4A. Nafion allows the passage of water vapor but has no effect on CO2 or major components of air and these dryers work especially well at low temperatures (Leckrone and Hayes, 1997). The capacity of these dryers was designed to provide drying of water saturated samples at 0 ◦C for several years of sampling. Laboratory tests indicate that the absolute water vapor dilution of the samples was equivalent to less than 0.1 ppm CO2 and that the difference between the water vapor pressure of the standards and the samples was on the order of 0.005 kPa, thus generating uncertainties on the order of 0.02 ppm in the final CO2 results. Water vapor changes in the gas stream were estimated with a humidity sensor designed for measurement of low humidity (Humirel HM1520LF) mounted in the outlet of the infrared analyzer. A complete sampling cycle consisted of several distinct operations that are described below:

Power is applied to the infrared analyzer which has a “warm up” time of one minute. While waiting for the analyzer to stabilize, the valves in the gas manifold are switched to form a closed loop with the analyzer, pump, a soda lime (mostly Ca(OH)2) cartridge and the Nafion dryers. The pump is started up and the trapped gas is circulated for one minute until all CO2 has reacted with the soda lime and removed from the gas stream. A reading of all parameters (CO2, cell temperature, pressure and water vapor) is made immediately before turning the circulation pump off. A second reading is taken 10 s later; those readings are used in the final calculations of pCO2 since they occur in a more noise-free environment and at a cell pressure that is closer to the ambient atmospheric pressure. Comparison of the two measurements allowed an estimate of pump effectiveness and the condition of the in-line filters. The zero values had a predictable offset of 1.2 ppm ◦C−1 and had a long-term drift of about 0.3 ppm per month.

After determining the instrument response at zero CO2 levels, two gas standards are analyzed sequentially. To conserve standard gases this analysis was performed during alternate sample cycles. The gases were contained in 1 L aluminum cylinders with stainless steel manifolds at an initial pressure of about 120 atm, thus yielding slightly less than 120 L of calibration gas at the deployment conditions. Delivery was controlled with a small two stage regulator (Scott Specialty Gases Model 14, after 2011 Beswick Engineering PRD3HP) coupled to a needle valve. Flow rates were set to 100 mL min−1 near the expected internal buoy temperature ( 1 ◦C) and tested over a temperature range of -40 ◦C to 24 ◦C. Gas delivery increased with decreasing temperature at a rate of about 1% per degree and good flushing of the analytical system was maintained under all conditions. During a standard cycle the valve manifold opens a path from one of the standard cylinders through the Nafion dryers and into the infrared analyzer. The exhaust is vented to the outside via the outer shell of the atmospheric sampling inlet. Gas flows for one minute after which valves are switched to vent any overpressure to the atmosphere. The procedure is then repeated for the second cylinder. Data were collected when the gas is flowing and when it is stopped and the pressure difference between the two readings is a measure of gas flow. No change in flow rate was detected during the 6 month test phase. The standards indicate that instrument sensitivity at the 400 ppm CO2 level decreased at a rate of about 0.4 ppm per month during the deployment.

Following the standard gas analysis, the valve manifold is switched into air sampling mode. In this mode, air is aspirated from the external inlet located on the buoy mast and then passes through the Nafion dryers before entering the infrared analyzer. The exhaust gases exit via the outer shell of the coaxial inlet line. The sample is actively pumped for one minute to flush the analytical manifold. Data were collected before turning the pump off and again after a 10 s relaxation period. Air enters the inlet system near the top of the buoy mast through a protected hydrophobic 0.45 micron pore size membrane (Pall Supor-450R). The air then enters a length of Nafion tubing in a small chamber which contains the exhaust gas. Since the exhaust gas is always drier than ambient air, the freshly sampled air will have some of its moisture removed and is less likely to form ice in the inlet line while traveling down the mast. The inlet line from the top of the mast to the instrumentation consists of coaxial FEP tubing with the incoming air flowing down in the center and the warmer exhaust gas flowing up in the sheath. This arrangement aids in the temperature equilibration of the incoming air and may decrease the possibility of ice formation in the incoming gas stream; an additional benefit is better organization of tubing inside the mast. Data from the pressure sensor while the system was being pumped indicate that the intake filter and gas path remained unobstructed during the entire deployment.

Before removing power from the analytical system, a final zero CO2 measurement is obtained in a manner identical to the zero obtained at the start. This procedure put the system in an identical rest state between samples and also provides another temperature calibration point since the final temperature is about one degree higher than the starting temperature.

Prior to deployment the instrument was placed in an environmental chamber and subjected to temperatures as low as -35 ◦C to examine the limits of operation. At temperatures below -25 ◦C the gas switching valves became unreliable and power consumption of the gas circulation pump increased; the infrared analyzer continued to operate reliably at all temperatures. Since it was expected that the internal buoy temperature would remain near the freezing point of seawater (-1.9 ◦C), we limited the testing and calibration to temperatures between -20 ◦C and 5 ◦C. During the Barrow deployment the temperature of the CO2 instrument ranged from 0.5 ◦C to 2.8 ◦C. Laboratory calibration consisted of operating the instrument at a variety of temperatures (-20 ◦C to 5 ◦C) and supplying it with up to six standard gases ranging from 200 ppm to 600 ppm CO2 in air. The gases were obtained from the National Oceanic and Atmospheric Administration’s (NOAA) Earth Systems Research Laboratory (ESRL). The calibration obtained in the laboratory was augmented in the field with a 3-point calibration done via a soda lime chamber to generate a zero standard and two small, high pressure CO2 gas standards contained in the buoy housing. The two gas standards (368.6 and 396.6 ppm supplied by ESRL) spanned the annual range of pCO2 that has been observed at the NOAA Barrow Observatory in recent years. In later deployments the range of standards was expanded to cover the increasing atmospheric pCO2 concentration. Standard gas calibrations were performed 4 times per day throughout the campaign and a 24 h running mean was utilized to make final adjustments to the data stream. Deployment data also indicated that there was a small residual pressure correction that was not implemented in the original infrared analyzer firmware. The pressure correction adjustment was derived empirically from the analysis of the standards during the deployment and then applied to the entire record. These data were compared to CO2 data collected at NOAA’s Barrow observatory. The agreement between the two data sets was consistently within 2 ppm.

Friederich, G. E., Brewer, P. G., Herlien, R., and Chavez, F. P.: Measurement of Sea-Surface Partial-Pressure of CO2 from a moored Buoy, Deep-Sea Res. Pt I, 42, 1175–1186, 1995. Friederich, G. E., Ledesma, J., Ulloa, O., and Chavez, F. P.: Air-sea carbon dioxide fluxes in the coastal southeastern tropical Pacific, Prog. Oceanogr., 79, 156–166, 2008. Leckrone, K. J. and Hayes, J. M.: Efficiency and temperature dependence of water removal by membrane dryers, Anal. Chem., 69, 911–918, 1997.

Donald Perovich principalInvestigator Patricia Matrai principalInvestigator Paul Shepson principalInvestigator William Simpson principalInvestigator Francisco Chavez principalInvestigator Collaborators from five institutions will work to build and deploy an Arctic Ocean network of rugged and autonomous buoys (named "O-Buoys"), capable of observing three key atmospheric chemical species, bromine monoxide-BrO, ozone-O3, and carbon dioxide-CO2 through 2016 (with each O-Buoy being operational for up to 2 years). O3 and CO2 are two of the most important greenhouse gases that have, as yet, poorly understood behavior in the Arctic. BrO is a reaction intermediate that is involved in the extraordinary ozone and mercury atmospheric depletion that occurs during polar springtime, both of which have strong consequences for human and ecosystem health in the Arctic region. These buoys are immersed through the sea ice into the ocean surface, thereby providing a constant temperature (-1.7 degrees C) environment for sensor stability. The original O-Buoy project funded by NSF included design and testing of the O-Buoy. In the current project, 11 new O-Buoys will be constructed and deployed along with the four already built. As a pilot project, two of the new O-Buoys will include seawater sensors for CO2, oxygen, pH, fluorescence, backscatter, temperature and salinity in addition to the atmospheric O3, BrO, and CO2 sensors. Throughout the project, data from each O-Buoy will be subject to QA/QC protocols by automated processing initially, with preliminary data available on a regular basis on the Advanced Cooperative Arctic Data and Information Service (ACADIS) site. All final data and metadata will be ultimately archived on ACADIS after final analysis at the end of each deployment. This network of O-Buoys, coordinated and clustered with other buoys in ice based observatories, will enable the scientific community to first observe and, next, better understand the impact of Arctic surface change on atmospheric composition and chemistry. Outreach to local K-8 schools will include an "Adopt-a-Buoy" program. Video footage from deployments/recoveries and interviews with colleagues and native Arctic people will be contributed to the ongoing http://www.arcticstories.net site, and activities and results will be communicated via the O-Buoy web site. 0611992 0612047 0612331 0612457 1022834 1022773 1023221 1023393 1023118