Environmental Engineering Reference
In-Depth Information
40000
50000
10/9/01 9:00
10/9/01 10:00
10/9/01 11:00
10/9/01 12:00
10/9/01 13:00
10/9/01 14:00
10/9/01 15:00
10/9/01 16:00
29/5/01 11:00
29/5/01 12:00
29/5/01 13:00
29/5/01 14:00
29/5/01 15:00
29/5/01 16:00
29/5/01 17:00
45000
35000
40000
30000
35000
25000
30000
20000
25000
20000
15000
15000
10000
10000
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5000
0
0
1
0
1
0
1
0
0
1
0
1
0
1
0
0
Dp (nm)
Dp (nm)
(a)
(b)
Figure 5.5
Particle number size distributions measured at Harwell, UK; days of nucleation:
(a) 29 May 2001; (b) 10 September 2001.
undergone a gas-to-particle conversion at nighttime low temperature and high rela-
tive humidity (Tolocka
et al.
, 2004b ).
Bursts of photochemically-formed particles have been observed in various envi-
ronments with various degrees of pollution such as the marine boundary layer and
coastal sites (Allen
et al.
, 1999 ; O ' Dowd
et al.
, 2002a, 2002c), in polar areas
and boreal forests (Mä kel ä
et al.
, 1997); in Mediterranean forests (Kavouras and
Stephanou, 2002), in continental areas (Birmili
et al.
, 2003), in industrial plumes
(Brock
et al.
, 2002), in urban areas (Woo
et al.
, 2001 ; Alam
et al.
, 2003) and in the
tropopause region (Young
et al.
, 2007). Recently Kulmala
et al.
(2004) and Holmes
(2007) provided comprehensive reviews of experimental observations of new par-
ticle formation and growth in the atmosphere spanning the various environments
and possible mechanisms. They underline that processes responsible for new par-
ticle formation by nucleation and subsequent growth depend on the environment
and are still not entirely understood.
Various nucleation mechanisms have been proposed and demonstrated in the
literature. The most widely studied are the binary water/sulfuric acid nucleation
(Vehkamä ki
et al.
, 2002) and the ternary water/sulfuric acid/ammonia nucleation
(Napari
et al.
, 2002 ; Merikanto
et al.
, 2007). Observations made in the free tropo-
sphere were consistent with the binary water/sulfuric acid nucleation theory
(Kulmala
et al.
, 2004), while it is likely that only ternary nucleation would be able
to explain particle formation in the low troposphere (Kulmala
et al.
, 2000 ; Korhonen
et al.
, 2003). Ion-induced nucleation (Yu and Turco, 2000) and the condensation of
semi-volatile organic compounds O' Dowd
et al.
, 2002b; Kavouras and Stephanou,
2002) are other demonstrated mechanisms. New particle formation from semi-
volatile organic compounds may include biogenic emissions, such as emissions of
organoiodine compounds from seaweeds at low tides (Allen
et al.
, 1999 ; O ' Dowd
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