Statistics overview
Summary of the trips :
A) ICAD: overall results
[ppbv]
[molec/cm^2]
[molec/cm^2]
[ppbv]
[ppbv]
The first graph (on the left) displays box plots of the concentration of NO2 at the ground for each day.
A substantial variation can be observed between the days, related to changes in emission and to
meteorological factors (such as wind and temperature). Those results were clearly influenced by local phenomenon such as traffic jams.
The second graph (on the right) displays the histogram of all the measurements.
NB: in both graphs the scale was adjusted to minimize the impact of outliers (max at 1400 [ppbv])
[ppbv]
[molec/cm^2]
B) DOAS: overall results
[molec/cm^2]
[molec/cm^2]
[molec/cm^2]
The first graph (on the left) displays the box plots of the integrated NO2 amount in the whole column of air above the bike. This device is less affected by the local perturbation than. The second graph (on the right) represents the histogram of all the measurements.
[molec/cm^2]
Analysis of the data :
A) Comparison morning and afternoon
The 2 maps of Brussels contain the grid of all data that were collected (overlapping places were subject of averaging). There is a clear distinction between the morning (first map) and the afternoon (second map) measurements. It appears that the concentration of NO2 in the column of air is more important during the morning than the afternoon.
B) Comparison between the ICAD and the DOAS
[ppbv]
[ppbv]
[molec/cm^2]
[molec/cm^2]
Looking back again at the box plots, if we keep only the same days for both it could seem that there is a certain correlation between the ground NO2 concentration and the concentration in the columns.
Drawing approximately a line passing through the median gives a similar shape in both graphs.
So, there could potentially be a correlation between both.
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C) The correlation between the ICAD and the DOAS
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The first graph (on the left) shows the correlation per day between the ICAD (VMR) and the DOAS (VCD). Some days like the day n°10 the factor of correlation is really high but other days like the fifth one shows barely no correlation. The scatter plot (on the right) displays a general coefficient of correlation of (0.569). The color of the points refer to the de density of point (the more reddish the more points there are).
D) Comparison with Tropomi satellite
The map (on the left) displays a superposition of the DOAS measurement (the lines) of concentration of NO2 smoothed and the measurement of Tropomi which is a satellite that take the same measures from the space ("pixels" on the map). The graph on the right displays the correlation between the DOAS and Tropomi measurements (taking into account only the measurements that have less that one hour of time difference for the same GPS location). The size of the points correspond to the length of the trip run through a single "pixel".
This graphs shows the integrated NO2 amount in the whole column of air measured (in blue) by the bike (DOAS) and (in orange) by Tropomi.
E) Comparison between the ICAD and the DOAS measurements
The 2 maps of Brussels contain the grid of all data that were collected by both the ICAD (on the left) and the DOAS (on the right). The concentration of nitrogen dioxide on the ground (ICAD) are alike the results of CurieuzenAir.
