CO2 monitoring on the roof of la Cité des sciences et de l'industrie

CO2 monitoring on the roof of la Cité des sciences et de l'industrie

Last hour average

411.5 ppm

ppm stands for "part per million": a 400 ppm CO2 concentration indicates
that there is 400 CO2 molecules into 1 million air molecules.
In other terms, the atmospheric CO2 concentration is 0.04%

The last three days

The inlet system from the monitoring station of Cité des Sciences is placed on the roof of the building in an urban environment, close to CO2 sources associated with several human activities. The measured CO2 atmospheric concentration is then most of the time high, over 400 ppm.
Diurnal cycles are often observed: CO2 concentration are growing beginning of the night and decrease with sunrise. Two mechanisms are involved in the diurnal cycles: daily variability of the local emissions due to human activities and/or vegetation and altitudinal stratification of the atmosphere. Indeed, during the night, a temperature gradient generally develops in the first tenth of meters above the ground. This thermal inversion with cold air masses at the ground is limiting the air mass mixing (convection) and stops the dispersion of constituent emitted at the surface. In these conditions, the measured concentrations at the surface, like those of CO2 are maximal during night, and then decrease as sun is rising up by atmospheric dilution. In addition to this atmospheric variability, one as to take into account the diurnal cycle of vegetation which absorbs CO2 during day time (photosynthesis) and breaths CO2 during night.
In case of strong wind, the diurnal cycle is less visible because there is a more strong dispersion of CO2.

CO2 monitoring on the roof of "La cité" and elsewhere

for one year, new page see since 1981 for one year, new page since 1992, new page

The last three days

For the last three monitoring days, we observe some diurnal cycles and/or remarkable events (sharp spikes) linked with intense human activities. Generally, the more close to urban environment a monitoring station is located, the more human activities are impacting the measurements. The station measuring air sampled from the roof of la Cité most often indicates the highest values (in black). The Amsterdam Island station (located in the middle of the Southern Indian Ocean) shows very little variability and low concentration (in red). The Mace Head station on the western coast is an intermediate station (in blue) and under the influence of major winds (west winds bring "clean" marine air masses, other wind directions bring air masses sensitive to local emissions).

Since November, 1st, 2014
(one year before monitoring on the Cité's roof)

Over years, the measurements show a seasonal cycle, more emphasized for the northern hemisphere like in Mace Head. See for this station how the CO2 concentration is decreasing during spring and summer of northern hemisphere (natural effect of the vegetation).

to see older records and understand