7Be and 210Pb Indicate an upper troposphere source for elevated ozone in the summertime subtropical free troposphere of the eastern North Atlantic

The relative abundance of 7Be and 210Pb in aerosols, represented as the “normalized fraction”, 7Be/(7Be + n210Pb), is unaffected by aerosol scavenging. This normalized fraction is an index of the relative influence on an air parcel of stratospheric and upper tropospheric processes versus those in the continental boundary layer (CBL). The high correlation of ozone concentration with the normalized fraction observed during the summer at Izaña, Canary Islands, indicates that 1) low altitude transport of air from the CBL is associated with low ozone concentrations; 2) high altitude transport through the troposphere from the CBL is associated with net ozone production; and 3) the stratosphere is not a direct source of a significant fraction of the ozone observed at Izaña during the summer.