DOI: 10.5285/5b75a1dc-6f24-43bc-b93a-c1dcf633f12a
title: Snow chemical compositions, salinity, surface ozone, BrO and meteorology data at Eureka, Canada in spring of 2018/19

description: Surface snow samples were collected daily from a Canadian high Arctic location at Eureka, Nunavut (80N, 86W) from the end of February to the end of March in 2018 and 2019. The snow samples were collected at several sites representing distinct environments: sea ice, inland close to sea level, and a hilltop ~600 m above sea level. Ion Chromatography (IC) analysis was performed for most of the snow samples. Snow salinity measurement is mainly for surface snow. Surface ozone was measured at sea level (from the Zero Altitude PEARL Auxiliary Laboratory (0PAL)) and lower tropospheric BrO (0-4 km) was measured by MAX-DOAS instrument (at ~610 m located at the Polar Environment Atmospheric Research Laboratory (PEARL)).

This study was supported by the UK NERC Arctic office via two UK-Canada bursary programs: "The role of tundra snowpack chemistry in the boundary layer bromine budget at Eureka, Canada" (2018), and "A second investigation of the role of tundra snowpack chemistry in the boundary layer 'bromine explosion'" (2019). The Eureka MAX-DOAS BrO measurements made at the PEARL Ridge Laboratory by CANDAC was primarily supported by NSERC, CSA, and ECCC.
description: Sampling site:
The snow was sampled at several sites representing distinct environments: sea ice, inland close to sea level, and a hilltop ~600 m above sea level (asl). All snow samples collected were transferred to 50 mL polypropylene tubes with screw caps (Corning CentriStar), which prior to field deployment had been rinsed with ultra-high-purity (UHP) water and dried in a class 100 clean laboratory in Cambridge, UK.

Ionic analysis:
All samples were only melted prior to the ion chromatography (IC) analysis, apart from a small portion of the samples that had been melted for salinity measurements. All 2019 samples were filtered using Millex-GP Express PES Membrane, Sterile, 33 mm, 0.22 µm filters (Merck Millipore Ltd., Cork, Ireland). The 2018 snow samples were analysed using Thermo Scientific Dionex ICS-4000 ion chromatography systems, with ions of Na+, Ca2+, Mg2+, K+, NH4+, Cl-, Br-, SO4=, NO3-, F-, acetate, formate, oxalate and MSA measured. The 2019 samples for IC analysis were run on a Dionex ICS-5000+ with ions of Na+, Ca2+, Mg2+, K+, Cl-, Br-, SO4=, NO3-, and MSA measured. Anion analysis was performed using an ionPac AS18-Fast-4 µm column, and cation analysis was performed using an IonPac CS12A column. Multiple samples were analysed to assess precision.

Snow salinity:
Snow salinity was measured using a conductivity meter (SensIon 5, Hach) with a measurement range of 0-200 mScm-1 and a maximum resolution of 0.1 µScm-1 at low conductivities (0-199.9 µScm-1). Conductivity values were converted into psu, approximately equivalent to the weight of dissolved inorganic matter in grams per kilogram of seawater.

MAX-DOAS measurements of BrO:
Multi-axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements of BrO partial columns were performed at the PEARL Ridge Lab. Spectra were recorded in the ultra-violet (UV) using a grating spectrometer (spectral resolution 0.45 nm) with a cooled (200 K) charge-coupled device (CCD) detector at 0.4-0.5 nm resolution. Elevation angles of 30°, 15°, 10°, 5°, 2°, 1°, and -1° were used in the elevation scans, and measurements were only taken with solar elevation above 4°. Differential slant column densities (dSCDs) of BrO and the oxygen dimer (O4) were retrieved using the DOAS technique. dSCDs were converted to profiles using a two-step optimal estimation method. The retrievals were performed for 0-4 km altitude on a grid with 0.2-km resolution. Due to the elevation of the measurement site, the instrument often measures BrO in the free troposphere, except during strong wind episodes and storms that generate a deep boundary layer (Bognar et al., 2020).

Surface ozone:
Surface ozone measurements were made by a TEI 49i ozone analyzer deployed at 0PAL.

Meteorology data:
There are two sets of local meteorology data used: one from EWS (the archived data are available at Historical Data - Climate - Environment and Climate Change Canada (ECCC) (weather.gc.ca)) and one from the PEARL Ridge Lab. The PEARL data is not open to the public; to access the data, contact Pierre Fogal at the University of Toronto. The UV index measured during the campaign period in 2018 and 2019 is from the ECCC Brewer spectrophotometer (https://doi.org/10.1029/2004JD004820).
description: Instrumentation:

Ionic analysis: Thermo Scientific Dionex ICS-4000 ion chromatography systems for 2018 samples and Dionex ICS-5000+ for 2019 samples
Conductivity meter: SensIon 5, Hach
BrO profile: Multi-axis Differential Optical Absorption Spectroscopy (MAX-DOAS)
Surface ozone: TEI 49i ozone analyzer
description: In the ionic analysis for 2019 samples, the limit of detection (LOD) is 3 times standard deviation of filter blank average peak area, and the limit of quantification (LOQ) is 10 times standard deviation of filter blank average peak area for all sequences (~40 samples analysed per sequence). The LOD of Br- is 0.200 um with a relative standard deviation of 0.023 um and the LOD of NO3- is 0.484 um with a relative standard of deviation of 0.037 um.

The accuracy of snow salinity as stated by the manufacturer is +/-0.001 psu at low salinities (&lt;1 psu).