ACT-America: L2 In Situ Atmospheric Gas Concentrations from Flasks, Eastern USA

This dataset provides atmospheric carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), molecular hydrogen (H2), nitrous oxide (N2O), sulfur hexafluoride (SF6), and other trace gas mole fractions (i.e. "concentrations") from airborne campaigns over North America for the NASA Atmospheric Carbon and Transport - America (ACT-America) project. ACT-America's mission spans five years and includes five six-week field campaigns covering all four seasons and three regions of the central and eastern United States. Two instrumented aircraft platforms, the NASA Langley Beechcraft B200 King Air and the NASA Goddard Space Flight Center's C-130 Hercules, are used to collect high-quality in situ measurements across a variety of continental surfaces and atmospheric conditions. The data were derived from laboratory measurements of whole air samples collected by Programmable Flask Packages (PFP) onboard the two ACT-America aircraft.

ACT-America's objectives are to study the transport and fluxes of atmospheric CO2 and CH4. At times they flew directly under Orbiting Carbon Observatory-2 (OCO-2) overpasses to evaluate the ability of OCO-2 to observe high-resolution atmospheric CO2 variations. 

There are a total of 312 files in this dataset. There are 156 data files in NetCDF (*.nc) file format and 156 data files in ICARTT (*.ict) file format. Note that files in both formats contain the same atmospheric gas concentration data but the ICARTT files contain no aircraft navigation and meteorological data.

This dataset currently includes results from the Summer 2016, Winter 2017, Fall 2017, and Spring 2018 campaigns. New and updated data will be added as it becomes available.

This dataset provides atmospheric carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), molecular hydrogen (H2), nitrous oxide (N2O), sulfur hexafluoride (SF6), and other trace gas mole fractions (i.e. "concentrations") from airborne campaigns over North America for the NASA Atmospheric Carbon and Transport - America (ACT-America) project. ACT-America's mission spans five years and includes five six-week field campaigns covering all four seasons and three regions of the central and eastern United States. Two instrumented aircraft platforms, the NASA Langley Beechcraft B200 King Air and the NASA Goddard Space Flight Center's C-130 Hercules, are used to collect high-quality in situ measurements across a variety of continental surfaces and atmospheric conditions. The data were derived from laboratory measurements of whole air samples collected by Programmable Flask Packages (PFP) onboard the two ACT-America aircraft.

Project:  Atmospheric Carbon and Transport (ACT-America)

The ACT-America, or Atmospheric Carbon and Transport - America, project is a NASA Earth Venture Suborbital-2 mission to study the transport and fluxes of atmospheric carbon dioxide and methane across three regions in the eastern United States. Each flight campaign will measure how weather systems transport these greenhouse gases. Ground-based measurements of greenhouse gases were also-collected. Better estimates of greenhouse gas sources and sinks are needed for climate management and for prediction of future climate.

Spatial Coverage: Flights over eastern and central United States

Spatial Resolution: Point measurements

Temporal Coverage: Periodic flights took place during each intensive campaign.

Campaign	Beginning and ending dates
Summer 2016	2016-07-11 to 2016-08-28
Winter 2017	2017-01-21 to 2017-03-10
Fall 2017	2017-10-03 to 2017-11-13
Spring 2018	2018-04-12 to 2018-05-20

Temporal Resolution: Approximately 10-12 flask samples were captured during each flight.

Study Area: (These coordinates are the approximate locations of the study sites and may not match the extent of the data files. All latitude and longitude are given in decimal degrees.)

Site	Northern Extent	Southern Extent	Western Extent	Eastern Extent
Central and Eastern United States	49.108	27.230	-106.494	-73.399

 

Dataset Information

There are 156 data files in netCDF (*.nc) version 4 format following CF conventions 1.6. NetCDF files are structured as GeoTrajectory files, where the observations for a flight segment are connected along a one-dimensional track in space, with time increasing monotonically along the track. These files contain gas concentrations and data from the respective aircraft’s flight navigation system. The flight and altitude data were imported from the ACT-America P3-B Data System (for B200 flights) and Housekeeping data (for C130 flights).

There are 156 data files in the ICARTT file format (*.ict). ICARTT files have detailed header information and follow the standards established and summarized in the ICARTT File Format Standards V1.1. https://www-air.larc.nasa.gov/missions/etc/IcarttDataFormat.htm. The files contain the same atmospheric gas concentration data as the NetCDF files, without the additional navigational or meteorological information.

Naming conventions are the same for both file formats. Files are organized by instrument and aircraft for the flight(s) on a given date.

ACT-America file naming convention

File names are standardized by:

ACTAMERICA-PFP-aircraft_YYYYMMDD_R#_L#.ext

where:

aircraft = either 'B200' or 'C130'

YYYYMMDD = flight date in UTC time

R# = revision number of data. A higher number indicates a more recent revision; e.g. R1 = revision 1

L# = optional launch number. Some flights had more than one segment or launch; e.g. L1 = launch 1

ext = file extension. either '.nc' for NetCDF or '.ict' for ICARTT

Companion Files

Additional information on the aircraft platforms deployed by ACT-America is provided in the accompanying files: Platform_B200.pdf, and Platform_C130.pdf.

 

Data Dictionary:

Gas variables present in both ICARTT and netCDF files:

Variable Name	Description	Units
CHLF_MoleFraction_PFP	Chloroform mole fraction	ppt
BRFM_MoleFraction_PFP	BRFM mole fraction	ppt
C2H6_CAMS2	Ethane mole fraction	ppt
CCl4_MoleFraction_PFP	CCI4 mole fraction	ppt
CS2_MoleFraction_PFP	CS2 mole fraction	ppt
F112_MoleFraction_PFP	F112 mole fraction	ppt
F124_MoleFraction_PFP	F124 mole fraction	ppt
F141B_MoleFraction_PFP	Dichlorofluoroethane mole fraction	ppt
HF21_MoleFraction_PFP	HF21 mole fraction	ppt
NF3_MoleFraction_PFP	NF3 mole fraction	ppt
SF6_MoleFraction_PFP	Sulfur Hexafloride mole fraction	ppt
HF22_MoleFraction_PFP	HF22 mole fraction	ppt
nC6H14_MoleFraction_PFP	n-Hexane mole fraction	ppt
PCE_MoleFraction_PFP	Perchloroethylene mole fraction	ppt
SF6_CCGG_MoleFraction_PFP	Sulfur Hexafloride mole fraction	ppt
BENZ_MoleFraction_PFP	Benzene mole fraction	ppt
C2F6_MoleFraction_PFP	Hexafluorethane mole fraction	ppt
C2H2_MoleFraction_PFP	Acetylene mole fraction	ppt
C2H6_MoleFraction_PFP	Ethane mole fraction	ppt
C3H8_MoleFraction_PFP	Propane mole fraction	ppt
CF4_MoleFraction_PFP	Carbon Tetrafloride mole fraction	ppt
CH2BrCl_MoleFraction_PFP	Bromochloromethane mole fraction	ppt
CH3I_MoleFraction_PFP	Methyl Iodide mole fraction	ppt
CH4_MoleFraction_PFP	Methane mole fraction	ppb
CH4C13_PFP	C-13 of CH4	permil
CO_MoleFraction_PFP	Carbon Monoxide mole fraction	ppb
CO2_MoleFraction_PFP	Carbon Dioxide mole fraction	ppm
DIBR_MoleFraction_PFP	Dibromomethane mole fraction	ppt
DICL_MoleFraction_PFP	Dimethyl Chloride mole fraction	ppt
F113_MoleFraction_PFP	F113 mole fraction	ppt
F115_MoleFraction_PFP	F115 mole fraction	ppt
F11B_MoleFraction_PFP	F11 mole fraction	ppt
F125_MoleFraction_PFP	Pentafluoroethane mole fraction	ppt
F13_MoleFraction_PFP	F13 mole fraction	ppt
F134A_MoleFraction_PFP	Tetrafluoroethane mole fraction	ppt
F143a_MoleFraction_PFP	1-1-1-Trifluoroethane mole fraction	ppt
F152A_MoleFraction_PFP	1-1-Difluoroethane mole fraction	ppt
F227e_MoleFraction_PFP	F227 mole fraction	ppt
F23_MoleFraction_PFP	Fluoroform mole fraction	ppt
F236fa_MoleFraction_PFP	F236fa mole fraction	ppt
F32_MoleFraction_PFP	F32 mole fraction	ppt
F365m_MoleFraction_PFP	Pentafluorobutane mole fraction	ppt
FC12_MoleFraction_PFP	FC12 mole fraction	ppt
H1211_MoleFraction_PFP	Halon 1211 mole fraction	ppt
H1301_MoleFraction_PFP	Halon 1301 mole fraction	ppt
H2_MoleFraction_PFP	Hydrogen mole fraction	ppb
H2402_MoleFraction_PFP	Halon 2402 mole fraction	ppt
HF133a_MoleFraction_PFP	HF133a mole fraction	ppt
iC4H10_MoleFraction_PFP	isoButane mole fraction	ppt
iC5H12_MoleFraction_PFP	isoPentane mole fraction	ppt
MCFA_MoleFraction_PFP	MCFA mole fraction	ppt
MEBR_MoleFraction_PFP	Methyl Bromide mole fraction	ppt
MECL_MoleFraction_PFP	Methyl Chloride mole fraction	ppt
N2O_MoleFraction_PFP	Nitrous Oxide mole fraction	ppb
nC4H10_MoleFraction_PFP	neoButane mole fraction	ppt
nC5H12_MoleFraction_PFP	neoPentane mole fraction	ppt
OCS_MoleFraction_PFP	Carbonyl Sulfide mole fraction	ppt
P218_MoleFraction_PFP	P218 mole fraction	ppt
SO2F2_MoleFraction_PFP	Sulfuryl Fluoride mole fraction	ppt
TCE_MoleFraction_PFP	Trichloroethylene mole fraction	ppt
TOL_MoleFraction_PFP	Toluene mole fraction	ppt

 

Navigation and Meteorological variables only present in netCDF files:

Variable Name	Description	Units
Flight_ID	Flight identification (aircraft and flight date)
Aircraft_Sun_Azimuth	Platform azimuth angle	degree
Aircraft_Sun_Elevation	Solar elevation angle	degree
Cabin_Pressure	Air pressure of cabin	mb
Day_of_Year	Day of year	day starting Jan 1 UTC
Dew_Point	Dew point temperature	Celcius
Drift_Angle	Drift angle	degree
GPS_Altitude	Global Positioning System altitude	meters
GPS_Time	Time	hours since 2016-01-01 00:00:00.0 UTC
Ground_Speed	Platform speed with respect to ground	meters per second
Indicated_Air_Speed	Indicated air speed	kts
Latitude	Latitude	degree north
Longitude	Longitude	degree east
Mach_Number	Mach number	mach
Mixing_Ratio	H2O mixing ratio	g per kg
Part_Press_Water_Vapor	Water vapor partial pressure in air	mb
Pitch_Angle	Platform pitch angle	degree
Potential_Temp	Potential temperature	Celcius
Pressure_Altitude	Barometric altitude	ft
Relative_Humidity	Relative humidity	percent
Roll_Angle	Platform roll angle	degree
Sat_Vapor_Press_H2O	H2O saturation vapor pressure of water	mb
Sat_Vapor_Press_Ice	H2O saturation vapor pressure of ice	mb
Solar_Zenith_Angle	Solar zenith angle	degree
Static_Air_Temp	Static air temperature	Celcius
Static_Pressure	Air pressure	mb
Sun_Azimuth	Solar azimuth angle	degree
Total_Air_Temp	Total air temperature	Celcius
Track_Angle	Track angle	degree
True_Air_Speed	Platform speed with respect to air	kts
True_Heading	Platform yaw angle	degree
Vertical_Speed	Vertical speed	ft per minute
Wind_Direction	Wind direction	degree
Wind_Speed	Wind speed	m per second
Altitude_AGL_m	Aircraft altitude above ground level	m
Ground_Elevation_m	Ground elevation above mean sea level	m

ACT-America, or Atmospheric Carbon and Transport – America, will conduct five airborne campaigns across three regions in the eastern United States to study the transport of atmospheric carbon. The eastern half of the United States is a region that includes a highly productive biosphere, vigorous agricultural activity, extensive gas and oil extraction and consumption, dynamic, seasonally varying weather patterns and the most extensive carbon cycle and meteorological observing networks on Earth, serves as an ideal setting for the mission.

Each 6-week campaign will accurately and precisely quantify anomalies in atmospheric carbon, also known as carbon flux. Accurate carbon flux data is necessary to address all terrestrial carbon cycle science questions. ACT-America addresses the three primary sources of uncertainty in atmospheric inversions — transport error, prior flux uncertainty and limited data density.

ACT-America will advance society’s ability to predict and manage future climate change by enabling policy-relevant quantification of the carbon cycle. Sources and sinks of atmospheric carbon dioxide (CO2) and methane (CH4) are poorly known at regional to continental scales. ACT-America will enable and demonstrate a new generation of atmospheric inversion systems for quantifying CO2 and CH4 sources and sinks.

Figure 2.  A schematic showing ACT-America project goals.

ACT-America Goals:

1. To quantify and reduce atmospheric transport uncertainties.
2. To improve regional-scale, seasonal prior estimate of CO2 and CH4 fluxes.
3. To evaluate the sensitivity of Orbiting Carbon Observatory (OCO-2) column measurements to regional variability in tropospheric CO2.

ACT-America will achieve these goals by deploying airborne and ground-based platforms to obtain data that will be combined with data from existing measurement networks and integrated with an ensemble of atmospheric inversion systems. Aircraft instrumented with remote and in situ sensors will observe how mid-latitude weather systems interact with CO2 and CH4 sources and sinks to create atmospheric CO2/CH4 distributions. A model ensemble consisting of a mesoscale atmospheric transport model with multiple physics and resolutions options nested within global inversion models and surface CO2/CH4 flux ensembles will be used to predict atmospheric CO2 and CH4 distributions.

Beyond the conclusion of the mission, application of the knowledge gained from this mission will improve diagnoses of the carbon cycle across the globe for decades.

Within the data, nodata and out-of-range values are provided in the dataset as described. Instrument precision specifications are available in the ACT-America proposal and replicated below (Fig 3.)

Figure 3.  Instrument precision table as provided in the ACT-America proposal.

See additional instrument quality control discussion here: https://www.esrl.noaa.gov/gmd/ccgg/aircraft/qc.html

ACT-America Overview

The eastern half of the United States, a region that includes a highly productive biosphere, vigorous agricultural activity, extensive gas and oil extraction, dynamic, seasonally varying weather patterns and the most extensive carbon cycle and meteorological observing networks on Earth, serves as an ideal setting for the mission. Flights will concentrate observations on three study domains: Northeast, South-central, and Midwest.

ACT-America will deploy the NASA C-130 and B-200 aircraft to measure atmospheric CO2 and CH4 in the atmospheric boundary layer (ABL) and free troposphere (FT). The mission proposes a total of 70 science flights, 528 hours for the C-130 and 396 hours for the B-200, dedicated in a roughly 3:3:1 ratio among fair weather, stormy weather, and OCO-2 underpass flight patterns.

For fair and stormy weather flights, the C-130 will fly at 3-8 km above ground, collecting in situ measurements in the lower FT, remotely sensed, column-averaged CO2 measurements focused on the ABL, and occasional in situ vertical profiles. The B-200 will primarily sample the ABL. For OCO-2 underflights, the C-130 will fly at 8 km above ground with the B-200 flying in the ABL, both along the OCO-2 flight track. The existing in situ tower CO2/CH4 observing network will be enhanced with five additional tower sites.

The mission will deliver 2-3 times more high-quality lower tropospheric CO2 and CH4 observations than any previous airborne campaign. 

Flight Plans

Data from the fair-weather flights are intended to quantify regional CO2 and CH4 fluxes, and to evaluate fair weather atmospheric C transport processes. The flight pattern is designed to provide extensive sampling of the ABL and lower FT in source/sink regions, meeting the requirements for the fair weather investigation. The C-130 aircraft will fly a U-shape pattern with flight legs perpendicular to the wind, sampling FT and ABL properties downwind of the sources and sinks of C. The C-130 will fly at roughly two times the midday ABL depth, (~3-4 km above ground level (AGL)) with periodic descents and ascents (5 to 10 times in a 6-8-hr flight) to sample the ABL. Although clear sky conditions will be targeted, the C-130 will conduct more profiling if low-altitude clouds interfere with the remote sensors. The B-200 aircraft will partake in two flights per day and will sample a subset of the C-130 flight path focusing on long transects in the ABL with periodic ascents to the FT. The two aircraft will operate over the same time period, but precise coordination is not required.

Data from stormy-weather flights will be used in combination with the data from fair-weather flights to evaluate the transport of C in the mid-latitudes. The flight plans include flight legs parallel to and crossing frontal boundaries at two or more altitudes, and crossing the frontal zone at two or more locations, meeting the requirements for the stormy weather investigation.

The pattern for the OCO-2 inter-comparison flights is designed to obtain data to evaluate the degree to which OCO-2 column CO2 measurements capture true spatial variability in column CO2 content over the continents. Two OCO-2 under flights will be conducted during each campaign and will be selected to cover varying surface reflectance, topography, and aerosol and cloud cover, all possible sources of bias in the OCO-2 measurements. The C-130 flights will be 1000 km in length and flown at 8 km (28 kft) altitude to maximize the fraction of the atmospheric column sampled by the MFLL. The B-200 aircraft will sample a shorter (~360 km) leg in the ABL, often the largest source of variability in column CO2. The B-200 flight will be centered with the C-130 and both aircraft will be vertically stacked during the OCO-2 overpass.

Airborne Instruments

ACT-America deployed high-quality, field-tested trace gas and meteorological instruments. This dataset includes measurements from discrete air samples captured by the flask sampling system onboard the aircraft. The two air-sampling devices, the Programmable Flask Package (PFP) and Programmable Compressor Package (PCP) systems, are used routinely on aircraft as part of the NOAA/ESRL Greenhouse Gas Reference network (Sweeney et al., 2015).

Flask air sampling system

 

Figure 4. Flask sampling system for aircraft measurements. Left: Programmable Flash Package (PFP) containing 12 flasks. Right: Programmable Compressor Package (PCP) containing pumps for pressurizing the flasks. (Image courtesy: http://www.esrl.noaa.gov/gmd/ccgg/aircraft/sampling.html)

A typical sampling routine uses one PCP and one or more PFP(s) that are pre-programmed with a flight-specific sampling plan of target altitudes for each sample. Sampling is timed to coincide with the overflight of a ground site of interest, or when interesting geophysical conditions are encountered. A map of flask sample locations is depicted in Figure 1. The PCP is connected to an LED display that communicates target sampling altitudes to the pilot. The pilot maintains the aircraft at a consistent altitude for the duration of each sample collection, typically under 40 seconds. For each sample, the inlet line and compression manifold are flushed with about 5 liters of ambient air. Valves on both ends of the current flask are then opened and the flask is flushed with about 10 more liters of ambient air to displace the dry, low CO2 fill gas with which the flasks are shipped. The sample flush air is measured by a mass flow meter to ensure that a sufficient volume passes through the manifold and flask before the downstream valve is closed and pressurization begins. Sample flush volumes and fill pressures during sampling are recorded by the data logger, along with ambient temperature, pressure, and relative humidity. GPS position and time stamp are also recorded with each sample.

ICARTT files have detailed header information and follow the standards established and summarized in the ICARTT File Format Standards V1.1. https://www-air.larc.nasa.gov/missions/etc/IcarttDataFormat.htm

Sweeney et al., 2015: Seasonal Climatology of CO2 across North America from aircraft measurements in the NOAA/ESRL Global Greenhouse Gas Reference Network, J Geophys Res Atmos, 120, 5155-5190, https://doi.org/10.1002/2014JD02259