Fig. A1.
Schematic diagram of the air sampling analysis line for the measurement of CO2, CH4 and CO concentrations by "PICARRO" at Lamto.
Table 1.
Bias and standard deviation calculated for CO2 and CH4 (2008–2018) and CO (2014–2018) during the quality control process at LTO station.
Table 2.
Reference of the NOAA (ASC, ASK, IZO) and LTO stations for CO2, CH4 and CO concentration measurements.
Table 3.
Mean amplitudes of monthly diurnal variations of CO2, CH4 and CO at Lamto over the 2008–2018 period.
Table 4.
Mean annual values and peak-to-peak amplitudes of CO2, CH4 and CO measured concentrations at LTO, ASC, ASK, IZO and CVO stations over the 2008–2018 period.
Fig. 1.
Localisationn of the ASC, ASK, IZO monitoring stations from the NOAA network and from the Lamto reserve (6°31 N et 5°02 W). Picture on the right was taken from the top of the sampling tower (Adapted from Tiemoko et al., 2020b).
Fig. 2.
Monthly means of Air Temperature in °C (red) and rainfall in mm (blue) at Lamto over the period 2008–2018. GSS, GSP, PSS and PSP are the great dry season, the great wet season, the short dry season and the short-wet season, respectively.
Fig. 3.
Average retro-plumes of air masses arriving at the station of LTO in the main dry (a) and wet (b) seasons during the 2014–2017 period. In blue, the LTO station.
Fig. 4.
View of the 50 m high tower. Meteorological sensors are installed at the top of the tower, together with the air intake.
Fig. 5.
Time series of atmospheric CO2 (a), CH4 (b) and CO (c) concentrations measured at the LTO station over the 2008-2018 period. The blue colour represents day-time data (from 11 h to 17 h) and the black colour represents night-time data (from 17 h to 11 h). The vertical lines differentiate years.
Fig. 6.
Seasonal diurnal cycles of (a) CO2, (b) CH4 and (c) CO measured at Lamto (GMT) over the 2008-2018 period (for CO2 and CH4) and over the 2014-2018 period (for CO).
Fig. 7.
Change of (a) CH4 (ppb) and (b) CO2 (ppm) concentrations recorded at the LTO station from May 2008 to August 2018 as a function of length of time window (y-axis) and ending of year of calculation. The inside of the black contours shows significant areas with a 95% confidence level from the student’s t-test.
Fig. 8.
Annual growth rate of CO2 (a) and CH4 (b) in the stations LTO, CVO, IZO, ASK et ASC. Due to lack of data, growth rates for some years are not presented.
Fig. 9.
Mean monthly variations and year-to-year trends of the (a and b) CO2, (c and d) CO and (e and f) CH4 molar fractions observed at the LTO station over the 2008–2018 period compared to those obtained at the ASC, ASK, IZO and CVO stations. It is noted that this analysis is based on daytime data only. Shaded areas of colour represent the estimated uncertainty in the average annual seasonal cycle. This estimate is based on the standard difference between the monthly mean values.
Fig. 10.
Mean monthly variations (in black lines) of (a) ΔCO2/ΔCO, (b) ΔCH4/ΔCO and (c) ΔCH4/ΔCO2 obtained from the dispersion pattern slopes between the CO2, CH4 and CO residues at the LTO station over the 2014-2018 period. The numbers in red are the correlation coefficients between each pair of species. Vertical black bars represent standard deviation.
Fig. 11.
Hourly variations of CO (red), CO2 (blue) and CH4 (black) concentrations from 10 to 19 December 2014 observed at the LTO station. Vertical gray shading corresponds to periods of high (December 13, 2014) and low (December 16–17, 2014) CO2, CH4 and CO concentration values that appear simultaneously and for which back-trajectories have been traced.
Fig. 12.
Average footprints for air masses arriving at the station from December 16th to 17 h and from 13th to 14th. The Lagrangian Particle Dispersion Model (LPDM) FLEXPART Version 9.0 in backward mode, forced by ECMWF wind fields with 0.5° × 0.5° spatial and 3 h temporal resolution is used to simulate the footprints (Stohl et al., 1998 ; Berchet et al., 2015). Inverse simulation consists of 1000 particles released at 1-hourly times steps over a day from the Lamto sampling inlet position (lon = –5.0278, lat = 6.2244, alt = 50m) and followed ten days backward in time (following Paris et al., 2010).
Fig. 13.
72-Hour retrotrajectoires of the air masses observed at the LTO station on 13 and 17 December 2014 with an altitude of 50 m based on the GDAS weather data. The LTO station is represented by a star. The upper part of the figure shows the ground trace of the air masses path and the lower part represents the altitude of the air masses during transport. The positions and altitude of the air masses are calculated every 6 hours.
Table A1. List of the three calibration scales used at Lamto between 2008 and 2020.