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GEM_CH4_Point_Source_Readme
Updated 05/26/2020
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The comma-delimited file GEM_CH4_Point_Source_Data.csv contains
airborne methane (CH4) concentration measurements from the GEM
study. The subset of GEM data included in the above file were employed
for point-source emission quantification as described in the following
manuscript:

Yu, X., D.B. Millet, K.C. Wells, T.J. Griffis, X. Chen, J.M. Baker,
S.A. Conley, M.L. Smith, A. Gvakharia, E.A. Kort, G. Plant, and J.D.
Wood (2020), Top-down constraints on methane point source emissions
from animal agriculture and waste based on new airborne measurements
in the US Upper Midwest, J. Geophys. Res., 125, e2019JG005429,
doi:10.1029/2019JG005429.

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Measurement description
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Flights were conducted on a fixed-wing, single-engine Mooney aircraft
with air sampling inlets on the outboard wing section. The instrument
payload included a cavity ring-down spectrometer (Picarro CRDS; model
G2301 during GEM-1, model G2210-m during GEM-2/3; Picarro Inc., Santa
Clara CA) providing ~1-3-second measurements of methane, ethane (GEM-2
and GEM-3 only), water vapor, and carbon dioxide. Calibrations were
performed using compressed ambient-level gas cylinders traceable to
NOAA Global Monitoring Division standards. Other on-board measurements
included temperature and relative humidity (model HMP60, Vaisala
Corp., Helsinki Finland), along with location, aircraft speed and
direction, pressure, wind speed and direction, and other flight
parameters provided by the avionics system and differential Global
Positioning System. Other measurements and sampling details are as
described in Yu et al. (2019).

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Contact
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Dylan Millet (dbm@umn.edu); Xueying Yu (yuxx0887@umn.edu)

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File description
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Data are provided in csv format with missing values denoted as -999999.
Variables included in the datafile are the following:
facility:             facility index
date:                 date of measurements
time.utc:             decimal day of year in utc (1.0000-365.9999)
alt.asl.m:            altitude above mean sea level in meters
heading.deg:          aircraft magnetic compass heading direction in
		      decimal degrees
u.m.s:                west-east wind in m/s
v.m.s:                south-north wind in m/s
zonal.speed.m.s:      zonal speed from GPS
meridional.speed.m.s: meridional speed from GPS
temp.c:               air temperature in degrees C
ch4.ppb:              CH4 mixing ratios in ppb

Other measurements from GEM flights are available from the authors
upon request.