Environmental Engineering Reference
In-Depth Information
Figure 13.1. Schematic diagram showing the effect of volcanic gases and
particles on the atmospheric composition and Earth
'
s climate. Adapted from Plate
1 of Robock (
2000
).
change (Jones
et al
.,
2007
), and
Chapter 17
discusses the environmental impacts
associated with ash deposition.
In contrast to airborne volcanic tephra, volcanic sulfuric acid aerosol particles
can alter the radiative balance of Earth on timescales relevant for climate change
due to their ability to scatter and absorb solar radiation (aerosol direct effect).
Sulfuric acid aerosol scatters radiation across the entire solar spectrum due to its
optical properties and typical particle radius of 0.5
μ
m (although there is a small
degree of absorption in the near-infrared spectrum). Once in the stratosphere,
volcanic sulfuric acid aerosol has a typical e-folding time of 9
-
12 months
for tropical eruptions and 2
4 months for high-latitude eruptions (Kravitz and
Robock,
2011
). The top of a stratospheric aerosol cloud absorbs solar radiation in
the near-infrared, whereas the lower stratosphere is heated by absorption of upward
thermal infrared radiation (Stenchikov
et al
.,
1998
). An aerosol cloud also forward
scatters some of the incoming solar radiation, resulting in enhanced downward
diffuse radiation, thereby increasing the sky
-
s brightness. The net radiative effect
of explosive volcanic eruptions is, however, a reduction in surface temperatures
because the scattering exceeds the absorption ef
'
ciency.
In the case of the 1991 eruption of Mount Pinatubo, stratospheric aerosol
concentrations remained elevated for about 2 years, and globally averaged strato-
spheric temperatures increased by around 2
-
3 K 3 months after the eruption
