Observations collected between 18th October 2018 and 29th March 2019 aboard Aurora Australis by AIRBOX and associated instruments

Full description

More information about these data is available in the word document in the download file. It is recommended that potential users of these data read this document before proceeding.

MAX-DOAS
This dataset comprises chiefly of solar scattered light spectra (level zero product) collected using a MAX-DOAS instrument. The MAX (Mult-Axis) refers to the fact that spectra are collected in a ‘set’ of elevation angle scans (-3, -2, -1, 0, 1, 2, 3, 5, 10, 20, 40, 90 deg). The DOAS (differential optical absorption spectroscopy) refers to the analysis method required for analysis of the scattered light spectra.
Briefly, analysis of these spectra relies on fitting absorption cross sections of trace gases of interest to determine the amount of trace gas integrated along the scattered light path, for each elevation angle in each set, using an appropriate fitting algorithm. This gives the slant column density for each trace gas at each elevation angle (level one product). The differential slant column density (dSCD) is determined by taking the ratio of low elevation angle scans with zenith scans, producing tropospheric specific information. Typically some atmospheric corrections are required to be included in the analysis including a polynomial, which accounts for broadband absorption and scattering processes, and corrections for the filling in of solar Fraunhofer lines (the Ring effect).
By inverting measured dSCDs, and dSCDS modelled using a radiative transfer model, vertical profile information for trace gases can be calculated using MAX-DOAS observations.
Finally, since knowing the elevation angle precisely is crucial to retrieval of vertical profile information from MAX-DOAS measurements, this dataset also includes Euler angles measured using a co-located accelerometer which may, if necessary, be used to correct MAX-DOAS elevation angles for the pitch and roll of the ship in the Southern Ocean.

MAX-DOAS instrument specifications:
Two ultra-low straylight 75mm Avantes spectrometers: UV: 295 – 450nm, 100 μm m slit (from fibre), 0.6nm resolution, Hamamatsu backthinned detector optimized for UV, Schott BG3 filter. Visible: 430 – 565nm, 100 μ m slit (from fibre), 0.6nm resolution, Sony 2048L detector
Typical instrumental stray light less than 0.05% , RMS of 1 · 10−4 (vis) and 2 · 10−4 (uv) for 1000 scans around noon.
Spectrometers temperature stabilized at a fixed temperature (20 C) with a deviation of less than 0.05 C
Elevation angle accuracy less than 0.1
Telescope field of view (opening angle) less than 0.3

Other instruments/datasets detailed in the file:
Gaseous oxidised mercury measurements
Gaseous elemental mercury
Radon measurements
HiVolume sampler
Ozone monitor
Sea state cameras
Lufft weather station
Spectronus greenhouse gas analyser
NAIS
ToF-ACSM
SMPS
Nephelometer
MAAP Black carbon analyser
CPC TSI 3776
CPC TSI 3772
CCNC
mini-MPL (micropulse lidar)
Microtops

Further information is available in the word document in the download file.

Lineage

Progress Code: completed

Statement: More information about the data quality is available in the word document in the download file. It is recommended that potential users of these data read this document before proceeding. MAX-DOAS Data Problems: The MAX-DOAS technique relies on precise knowledge of the viewing geometry. This is an inherent challenge of MAX-DOAS measurements on a moving vessel. The Envimes MAX-DOAS instrument used in this work has in-built elevation angle compensation firmware which for slowly varying pitch/roll of the ship works well, however in rough seas this is not always the case. Recommendation for data analysis: The spectral log files contain ‘start elevation angle’ and ‘end elevation angle’ fields. This can be used to calculate a difference whose absolute value should not be greater than 0.2 for confidence in the measured viewing geometry. Gaseous oxidised mercury measurements Data Problems: None known so far. Gaseous elemental mercury Data Problems: Instrument Analytical Availability Baseline deviation (BLdev) during sampling did not exceed 0.1 mV indicating high instrument stability during the sampling period. Occasionally, users may experience a drop in the capture efficiency of one or both of their sampling cartridges. In some instances, an unknown compound may passivate the surface of the cartridge. The symptoms of this condition are as follows. - The two cartridges usually report substantially different readings while monitoring ambient levels. This condition is most evident when output is plotted. The graph assumes a characteristic "sawtooth" or bi-modal pattern. - The difference may slowly appear and the two cartridges may converge after a few days of continuous operation. - The calibrations often report good (low) ZERO A and B areas, and normal (i.e.: closely matched) SPAN A and B areas. The problem thus seems to occur only during monitoring, not calibrations. The differences observed in the collected dataset between TRAP A and TRAP B suggest that TRAP A was not working effectively from early on in the campaign (passivation of the Trap is a possibility or valve contamination ). The guidance from Tekran is we should accept the data from the "B" trap and discard the "A" trap data. This is in line with the guidance in the 2537B Tekran operations manual (10:21) "When the readings between the A and B gold cartridges differ, the gold cartridge showing the higher values has always been found to be accurate. Data from the offending gold cartridge can be stripped from the data set." Radon measurements Data Problems: The calibration/background unit was operated in manual mode during for most of the shipping season. This means that the flag column in the data is reported as zero. Find calibrations by looking for very high LLD values; find backgrounds for looking for extended periods when both InFlow and ExFlow are close to zero. HiVolume sampler Data Problems: - Snow fall - A lack of wind sector control to avoid sampling ship exhaust. Period of sampling were chosen based on atmospheric conditions and weather forecasts. Ozone Monitor Data Problems: Contamination from the ship exhaust was observed on many occasions, which causes large drops in the ozone concentration due to titration of atmospheric ozone with NOx within the exhaust. This contamination can also be determined from high particulates and CO concentrations sampled by other instrumentation located aboard the Aurora Australis e.g. the Spectronus Trace Gas and Isotope Analyser. Note that there is a recurrent feature in data from the ozone analyser that corresponds to a regular zero/span check that's programmed into the instrument. For example, between dates 17-Oct-2018 to 27-Nov-2018 look for the reoccurrence that happens for ~2 hrs every 4 days between 21:00 - 23:15 UTC. Sea state cameras Data Problems: None known so far. Lufft weather station Data Problems: None known so far. Spectronus greenhouse gas analyser Data problems: No substantial or prolonged problems leading to data loss. Short periods of poor quality or shutdown due to overheating of the met lab housing the analyser. Frequent contamination by ship’s exhaust. NAIS Data problems: No issues were encountered on V1, V2 and V4. During the first two weeks of V3, deposits of diesel soot within the instrument invalidated the number concentrations for several size bins, particularly for particles and clusters less than 4 nm in mobility diameter. The instrument was cleaned on 26th January 2019 and returned to normal working order ToF-ACSM Data problems: The filter switching servo failed during the voyage and was swapped out with a spare. The MD1 backing pump failed and required replacement membranes and valves. The instrument was out of operation 10-12 Nov 2018 SMPS Data problems: None known. Nephelometer Data problems: None known. MAAP Black carbon analyser Data problems: None known. CPC TSI 3776 Data problems: None known. CPC TSI 3772 Data problems: The nozzle pressure crept up during V1, likely due to nozzle becoming clogged with salt/exhaust. It didn’t go out of spec though, and will be cleaned during the port period. The butanol charcoal filter on the fill bottle clogged up, creating a vacuum that prevented the automatic filling of the internal butanol reservoir to occur. The lid was left slightly open during the remainder of the voyage to prevent the vacuum occurring and this will be replaced during the port period. This issue lead to the butanol wick drying out and reported concentrations going to zero. CCNC Data problems: The instrument counts went to zero and flows were unstable after refilling the water reservoir on Nov 20, 2018. This issue fixed itself overnight. mini-MPL (micropulse lidar) Data Problems: There were some missing periods, of lost power. Occasionally the scanning unit rotated freely (in the azimuth only) but this had no noticeable effect on the data collection. Microtops Data problems: Required clear sky and stable conditions - difficult over the Southern Ocean where clouds often came across the sun in the middle of a measurement or sea-state was extreme and keeping the sun in target was challenging.