# AoM2023 SP-AMS Submicron Aerosol Composition
# ARTofMELT 2023 Expedition -- IB Oden, Fram Strait
# ============================================================

## Dataset description

Submicron non-refractory aerosol composition measured by a Soot-Particle
Aerosol Mass Spectrometer (SP-AMS, Aerodyne Research Inc.) during the
ARTofMELT 2023 expedition aboard the Swedish icebreaker Oden in the
Fram Strait region, 7 May to 14 June 2023.

The SP-AMS was deployed in the ACES (Atmospheric Chemistry and Earth
Sciences) container laboratory, sampling through a whole-air inlet and,
during cloud/fog events, through a Ground-based Counterflow Virtual
Impactor (GCVI). The CVI_status flag indicates whether the CVI was
active (1) or the total inlet was in use (0).

## Files

- AoM2023_SPAMS_submicron_composition_1min.csv
  Level 1: native ~1-minute time resolution, CE-corrected concentrations,
  per-minute pollution flag, CVI status, and ship position.

- AoM2023_SPAMS_submicron_composition_1hour.csv
  Level 2: 1-hour averages computed from clean, laser-OFF minutes only
  (not flagged as polluted; values <= 0 excluded, consistent with the
  original Igor Pro processing).

- AoM2023_SPAMS_submicron_composition.xlsx
  Excel workbook containing both levels on separate sheets.

## Column descriptions -- Level 1 (1-minute)

- datetime_UTC:     Timestamp (ISO 8601, UTC), floored to the minute
- latitude:         Ship latitude (decimal degrees N)
- longitude:        Ship longitude (decimal degrees E)
- Org_ug_m3:        Organic aerosol mass concentration (ug m-3)
- SO4_ug_m3:        Sulphate mass concentration (ug m-3)
- NO3_ug_m3:        Nitrate mass concentration (ug m-3)
- NH4_ug_m3:        Ammonium mass concentration (ug m-3)
- Chl_ug_m3:        Non-refractory chloride mass concentration (ug m-3)
- CVI_status:       1 = CVI active (cloud residuals), 0 = total inlet
- cvi_frac:         Fraction of the minute during which CVI was active
                    (0-1), derived from second-level CVI status data.
                    NA where CVI data are unavailable.
- pollution_frac:   Fraction of 10-second intervals within the minute
                    flagged as influenced by ship exhaust (0-1)
- pollution_flag:   Binary flag: 1 if any 10-second interval within
                    the minute was flagged as polluted, 0 otherwise

## Column descriptions -- Level 2 (1-hour)

- datetime_UTC:             Timestamp (ISO 8601, UTC), start of the hour
- latitude:                 Mean ship latitude during the hour
- longitude:                Mean ship longitude during the hour
- Org_ug_m3:                Organic aerosol (ug m-3), averaged from clean
                            laser-OFF minutes only (values <= 0 excluded)
- SO4_ug_m3:                Sulphate (ug m-3), clean laser-OFF average
- NO3_ug_m3:                Nitrate (ug m-3), clean laser-OFF average
- NH4_ug_m3:                Ammonium (ug m-3), clean laser-OFF average
- Chl_ug_m3:                Non-refractory chloride (ug m-3), clean
                            laser-OFF average
- CVI_status:               Majority CVI status for the hour (1 if CVI
                            active for >50%% of minutes)
- cvi_frac:                 Fraction of minutes within the hour during
                            which CVI was active (0-1), derived from
                            per-minute CVI_status flags. NA where CVI
                            data are unavailable.
- n_minutes_ams_laser_off:  Number of clean, laser-OFF minutes with valid
                            AMS data used to compute the hourly average.
                            Zero or NA indicates no usable data for that hour.
- pollution_frac:           Fraction of AMS minutes within the hour flagged
                            as polluted (0-1), computed over minutes where
                            the flag was available.

## Data processing

### Instrument
SP-AMS (Aerodyne Research Inc.) with tungsten vaporiser operated at
~600 degrees C. The intracavity Nd:YAG laser was operated in an alternating
ON/OFF cycle of 30 minutes per phase. The species concentrations reported
in this dataset (Org, SO4, NO3, NH4, Chl) are derived from laser-OFF
(beam-closed) measurement periods, corresponding to the standard
non-refractory AMS measurement mode. High-resolution mass spectra
processed using SQUIRREL 1.66G (UMR) and PIKA 1.26G (HR) in Igor Pro
6.37 (WaveMetrics, Inc).

### Collection efficiency
CE = 1.0224, determined by Deming regression (forced through origin) of
SP-AMS sulphate vs. ion chromatography sulphate from co-located
low-pressure impactor samples. All species are divided by this CE value.
The composition-dependent CE parameterisation of Middlebrook et al.
(2012) was not applied.

### Pollution filtering
Ship exhaust contamination was identified using a 10-second-resolution
pollution flag developed by Julia Kojoj, Stockholm University, based on
[brief method description]. The raw flag is aggregated to per-minute
(Level 1) and per-hour (Level 2) statistics.

In Level 2, hourly averages are computed from minutes where
pollution_flag = 0 (no pollution detected in any 10-second interval).
Minutes lacking pollution flag data are treated as clean. Users
requiring stricter filtering can use the Level 1 data and apply custom
thresholds on pollution_frac.

### CVI operation
A Ground-based Counterflow Virtual Impactor (GCVI) was operated during
cloud and fog events to sample cloud residual particles. When active,
the SP-AMS measured cloud residuals rather than total ambient aerosol.
CVI_status = 1 indicates periods of CVI operation. Users studying
ambient aerosol composition may wish to filter out CVI-on periods;
users interested in cloud residuals should select CVI_status = 1.

### Detection limits
Detection limits (DL) and limits of quantification (LOQ) were computed
following Drewnick et al. (2009), Eq. 4, using continuous beam-closed
signal variability, scaled from 60-second to 1-hour resolution as
DL_1hr = DL_60s / sqrt(60). Values are computed per aerosol period to
account for instrument drift.

Campaign-wide 1-hour values (ug m-3):
  Species   DL_1hr    LOQ_1hr
  Org       N/A       N/A     (see note)
  SO4       0.031     0.102
  NO3       0.002     0.006
  NH4       0.003     0.010
  Chl       0.040     0.134

Note: Negative and zero values in the Level 1 data reflect instrument
noise around zero and are retained for statistical consistency. They are
excluded from Level 2 hourly averages, consistent with the original
Igor Pro processing (Extract condition: var > 0). Organic aerosol DL
was not derived from beam-closed signal due to CO2 background correction
artefacts.

### Coordinate reference
Ship position from the Oden navigation system, reported at 1-minute
resolution. Latitude and longitude in decimal degrees (WGS84).

## References

Aiken, A. C. et al.: O/C and OM/OC ratios of primary, secondary, and
  ambient organic aerosols with high-resolution time-of-flight aerosol
  mass spectrometry, Environ. Sci. Technol., 42, 4478-4485, 2008.

Drewnick, F. et al.: A new Time-of-Flight Aerosol Mass Spectrometer
  (ToF-AMS) - instrument description and first field deployment,
  Atmos. Meas. Tech., 2, 33-46, 2009.

Middlebrook, A. M. et al.: Evaluation of composition-dependent
  collection efficiencies for the Aerodyne aerosol mass spectrometer
  using field data, Aerosol Sci. Technol., 46, 258-271, 2012.

Tjernstrom, M., Zieger, P., et al.: ARTofMELT 2023 - Expedition report.
  Swedish Polar Research Secretariat, ISBN 978-91-519-5134-8, 2025.
  https://urn.kb.se/resolve?urn=urn:nbn:se:polar:diva-9183

## Contact

Diego Fellin, Ca Foscari University of Venice & Institute of Polar
Sciences, Italian National Research Council
https://orcid.org/0009-0003-0323-8452
diego.fellin@unive.it

## License

Open Data Commons Attribution License (ODC-By) v1.0

## Acknowledgements

This work is part of the ARTofMELT (Atmospheric rivers and the onset of
Arctic melt) project. The ARTofMELT expedition was supported and organised
by the Swedish Polar Research Secretariat (SPRS) on the Swedish research
icebreaker Oden in spring 2023 under the SWEDARCTIC program. This project
has received funding from the European Union's Horizon 2020 research and
innovation programme under grant agreement No 101003826 via project CRiceS
(Climate Relevant interactions and feedbacks: the key role of sea ice and
Snow in the polar and global climate system) and the European Research
Council (Consolidator grant INTEGRATE No 865799).

