Investigating the Link Between Glyoxal and Biogenic Activities - Towards an Interdisciplinary Approach in Earth System Science - page 56

3 Results and Discussion

It is well known that one of main source of trace gases into the atmosphere are biogenic
emissions. The global maps of glyoxal show that high values are found over regions
such as south America, continental Africa, and south of Asia and, to lesser extend,
southeastern US, which correspond to areas with dense vegetation (see Fig. 1 ).
Around 55 % of global glyoxal amounts released to the atmosphere results from the
oxidation of biogenic VOC, where isoprene oxidation is responsible of 90 %, while
the remaining sources are ethane and monoterpenes (Stavrakou et al. 2009a ).
In order to investigate the link between glyoxal and biogenic activities, temporal
and spatial correlation coef cients between CHOCHO and enhanced vegetation

index (EVI) are computed, where EVI represents a measure of vegetation greenness,
a composite property of leaf chlorophyll, and canopy cover, which can be retrieved
from the MODerate resolution Imaging Spectroradiometers (MODIS) on board
NASAs Aqua satellite (Justice et al. 2002 ). Assuming a linear relationship between
CHOCHO VCs and EVI, monthly mean values of OMI CHOCHO VCs and EVI
MODIS with a grid resolution of 1.0 °× 1.0 ° were used in the calculations. Figure 2 ,

top left, shows a global map of correlation coef cients for the time period 2005

-
2012. The highest correlations between CHOCHO and EVI were found for two
regions (southeastern US and north of Africa), even correlation coef

-

cients larger

than 0.8 were found over these areas (see Fig. 2 , top right). Also, time series of

spatially averaged monthly means were computed for the two regions and are shown
in the Fig. 2 (bottom). The seasonal behaviour of glyoxal and EVI are in a good

-

Fig. 1 Global map of CHOCHO VCs retrieved from OMI measurements between 2005 and 2012