Documentation Revision Date: 2019-11-26
Dataset Version: 1
This dataset includes 94 files in comma-delimited text (ICARTT) format, with two files per flight.
Morgan, E.J., B.B. Stephens, J. Bent, A. Watt, S. Afshar, W. Paplawsky, and R.F. Keeling. 2019. ATom: L2 Measurements from Medusa Whole Air Sampler (Medusa). ORNL DAAC, Oak Ridge, Tennessee, USA. https://doi.org/10.3334/ORNLDAAC/1729
Table of Contents
- Dataset Overview
- Data Characteristics
- Application and Derivation
- Quality Assessment
- Data Acquisition, Materials, and Methods
- Data Access
This dataset provides O2/N2, CO2, Ar/N2, and stable isotope ratios of CO2 measured by the Medusa Whole Air Sampler during airborne campaigns conducted by NASA's Atmospheric Tomography (ATom) mission. ATom deploys an extensive gas and aerosol payload on the NASA DC-8 aircraft for systematic, global-scale sampling of the atmosphere, profiling continuously from 0.2 to 12 km altitude. Flights occurred in each of 4 seasons from 2016 to 2018. Medusa collected thirty two cryogenically dried, flow and pressure controlled samples per flight. Medusa provides discretely-sampled comparisons for onboard in situ O2/N2 ratio and CO2 measurements and unique measurements of Ar/N2 and 13C, 14C, and 18O isotopologues of CO2. The complementary measurements allow ground-truthing of onboard instrument measurements in a laboratory setting, where analysis conditions can often be more stringently controlled and carefully monitored. Isotope and argon measurements can provide additional information about land and ocean controls over the carbon cycle, and about the age and source of the air sampled.
The Atmospheric Tomography Mission (ATom) was a NASA Earth Venture Suborbital-2 mission. It studied the impact of human-produced air pollution on greenhouse gases and on chemically reactive gases in the atmosphere. ATom deployed an extensive gas and aerosol payload on the NASA DC-8 aircraft for systematic, global-scale sampling of the atmosphere, profiling continuously from 0.2 to 12 km altitude. Flights occurred in each of four seasons over a 4-year period.
ATom: Merged Atmospheric Chemistry, Trace Gases, and Aerosols. Data from all ATom instruments and all four flight campaigns, including aircraft location and navigation data, merged to several different time bases: https://doi.org/10.3334/ORNLDAAC/1581
ATom Flight Track and Navigational Data. Flight path (location and altitude) data for each of the four campaigns provided in KML and csv format: https://doi.org/10.3334/ORNLDAAC/1613
Spatial Coverage: Global. Flights circumnavigate the globe, primarily over the oceans
Spatial Resolution: Point measurements
Temporal Coverage: Periodic flights occurred during each campaign
Table 1. Flight campaign schedule
|ATom-1||July 29 - August 23, 2016|
|ATom-2||January 26 - February 21, 2017|
|ATom-3||September 28 - October 28, 2017|
|ATom-4||April 24 - May 21, 2018|
Temporal Resolution: each flask integrates over 25 seconds
Data File Information
This dataset includes 94 files in comma-delimited text (ICARTT) format, with two files per flight date for all four ATom flight campaigns. Data files conform to the ICARTT File Format Standards V1.1. Note: no data from the 2017-02-13 flight are available.
File names are structured as MEDUSA-Kernel_DC8_YYYYMMDD_R#.ict or MEDUSA_DC8_YYYYMMDD_R#.ict, where YYYYMMDD is the start date (in UTC time) of the flight and R# is the file version or revision number.
MEDUSA files contain measurements from flasks and the MEDUSA-Kernel files contain the averaging kernel used to generate the Mean_UTC timestamps provided in the corresponding MEDUSA file. There are 47 files of each type, one for each flight date. Missing data are indicated by -9999.000.
Table 2. Variables in the data files MEDUSA_DC8_YYYYMMDD_R#.ict.
|Start_UTC||seconds||seconds since UTC midnight when flask was opened|
|Stop_UTC||seconds||seconds since UTC midnight when flask was closed|
|Mean_UTC||seconds||kernel-weighted representative sampling time|
|position||integer||order of flasks taken (1-32)|
|upstream_pressure||torr||kernel-weighted pressure reading at upstream pressure controller|
|downstream_pressure||torr||kernel-weighted pressure reading at downstream pressure controller|
|bypass_pressure||torr||kernel-weighted pressure of bypass line|
|sample_pressure||torr||kernel-weighted representative pressure in sampling line|
|flow||L/min||kernel-weighted representative mean flow during sampling|
|flask_pressure||torr||fill pressure of each flask|
|O2N2_MED||per meg||deviations in the ratio of O2 to N2 on the Scripps O2 Laboratory O2 Scale|
|ArN2_MED||per meg||deviations in the ratio of Ar to N2 on the Scripps O2 Laboratory Argon Scale|
|O2N2star_MED||per meg||deviations in the ratio of O2 to N2 with thermal artifacts and variations due to air-sea exchange caused by solubility changes removed|
|CO2_MED||ppm||dry air mole fraction of CO2 on Scripps O2 Laboratory CO2 Scale|
|d13CO2_MED||per mil||deviation in the 13C/12C Stable Carbon Isotope Ratio in CO2 relative to Vienna Pee Dee Belemnite|
|d18OCO2_MED||per mil||deviation in the 18O/16O Stable Oxygen Isotope Ratio in CO2 relative to Vienna Pee Dee Belemnite|
|D14CO2_MED||per mil||deviation from the Modern standard 14C/C ratio|
Table 3. Variables in the data files MEDUSA-Kernel_DC8_YYYYMMDD_R#.ict.
|Start_UTC||seconds||seconds since UTC midnight on day of takeoff|
|Kernel||seconds||Weight in the averaging kernel. See Bent 2014 (PhD thesis, UCSD) for details.|
Application and Derivation
ATom builds the scientific foundation for mitigation of short-lived climate forcers, in particular methane (CH4), tropospheric ozone (O3), and Black Carbon aerosols (BC).
ATom Science Questions
- What are chemical processes that control the short-lived climate forcing agents CH4, O3, and BC in the atmosphere? How is the chemical reactivity of the atmosphere on a global scale affected by anthropogenic emissions? How can we improve chemistry-climate modeling of these processes?
- Over large, remote regions, what are the distributions of BC and other aerosols important as short-lived climate forcers? What are the sources of new particles? How rapidly do aerosols grow to CCN-active sizes? How well are these processes represented in models?
- What type of variability and spatial gradients occur over remote ocean regions for greenhouse gases (GHGs) and ozone depleting substances (ODSs)? How do the variations among air parcels help identify anthropogenic influences on photochemical reactivity, validate satellite data for these gases, and refine knowledge of sources and sinks?
ATom delivers unique data and analysis to address the Science Mission Directorate objectives of acquiring “datasets that identify and characterize important phenomena in the changing Earth system” and “measurements that address weaknesses in current Earth system models leading to improvement in modeling capabilities.” ATom will provide unprecedented challenges to the CCMs used as policy tools for climate change assessments, with comprehensive data on atmospheric chemical reactivity at global scales, and will work closely with modeling teams to translate ATom data to better, more reliable CCMs. ATom provides extraordinary validation data for remote sensing.
Uncertainty information is not provided.
Data Acquisition, Materials, and Methods
ATom makes global-scale measurements of the chemistry of the atmosphere using the NASA DC-8 aircraft. Flights span the Pacific and Atlantic Oceans, nearly pole-to-pole, in continuous profiling mode, covering remote regions that receive long-range inputs of pollution from expanding industrial economies. The payload has proven instruments for in situ measurements of reactive and long-lived gases, diagnostic chemical tracers, and aerosol size, number, and composition, plus spectrally resolved solar radiation and meteorological parameters.
Combining distributions of aerosols and reactive gases with long-lived GHGs and ODSs enables disentangling of the processes that regulate atmospheric chemistry: emissions, transport, cloud processes, and chemical transformations. ATom analyzes measurements using customized modeling tools to derive daily averaged chemical rates for key atmospheric processes and to critically evaluate Chemistry-Climate Models (CCMs). ATom also differentiates between hypotheses for the formation and growth of aerosols over the remote oceans.
Medusa Whole Air Sampler
Medusa collects 32 cryogenically dried, flow and pressure controlled samples per flight. The samples are collected by an automated sampler into 1.5 L glass flasks that integrate over 25-second (1 e-fold) periods. Medusa provides discretely-sampled comparisons for onboard in situ O2/N2 ratio and CO2 measurements and unique measurements of Ar/N2 and 13C, 14C, and 18O isotopologues of CO2. The complementary measurements allow ground-truthing of onboard instrument measurements in a laboratory setting, where analysis conditions can often be more stringently controlled and carefully monitored. Medusa consists of an onboard computer, two pressure controllers, two pumps, three multi-position selector valves, and a host of other hardware that control and direct the air samples. All air is dried by passing it through traps immersed in a -78 C dry ice bath, adjusted to match atmospheric pressure at sea level, and then automatically isolated in a flask. Medusa flasks are analyzed on a sector-magnet mass spectrometer and a LiCor non-dispersive infrared CO2 analyzer by the Scripps O2 Program at Scripps Institution of Oceanography.
These data are available through the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).
Contact for Data Center Access Information:
- E-mail: firstname.lastname@example.org
- Telephone: +1 (865) 241-3952
Bent, J.D. 2014. Airborne Oxygen Measurements over the Southern Ocean as an Integrated Constraint of Seasonal Biogeochemical Processes. UCSD PhD Thesis. Available at http://bluemoon.ucsd.edu/publications/jonathan/Bent_Dissertation__FINAL.pdf