Figure 3-7: Aerosol-mass column between 15- and 20-km
altitude, derived from backscatter measurements made by lidar at Garmisch-Partenkirchen,
Germany, between 1976 and end of 1998. Dates of major volcanic eruptions are
marked on the horizontal axis (H, St. Helens; A, Alaid; C, El Chich�n; R,
Ruiz; N, Nyamuragira; P, Pinatubo). The dashed line indicates the average
value of 1979, which can be considered a background value free from volcanic
influence (adapted from J�ger and Hofmann, 1991; J�ger et al., 1998).
