Chemistry Reference
In-Depth Information
Fig. 1 (a) Typical clean Northern European median number size distribution (measured at
SMEAR II station in Hyyti¨l¨, Finland). The approximate modal locations and size ranges of
different integral properties of the aerosol number size distribution used are shown; (b) variance of
number concentration as a function of particle diameter; (c) variance of (computed) volume
concentration in the same station (adapted from Asmi (2012), [
11
])
alveolar regions of lungs. The smaller diameter limit of 30 nm comes mostly
from trying to keep the instrumental datasets comparable. These particles have
generally relatively low lifetime (in the order of one or two days) and thus are
more representative of the local emissions.
• Particle number concentration between 50 and 500 nm of diameter (N
50
), which
represents particles from larger diameter end (i.e., more aged) Aitken mode,
together with the entire accumulation mode. The 500 nm upper limit is due to
instrumental limitations. These particles are representative of CCNs for high
updraft velocity clouds, as typical aged particles (
0.18) with 50 nm diame-
ter are activated with water supersaturation of 0.8%. The upper limit of 500 nm
is chosen to have comparable values for different instruments. As the particle
number size distribution over 500 nm of diameter is usually insignificant in
terms of number concentration in comparison with sub-500 nm size ranges
(Fig.
1a
), making the N
50
a good representative parameter of the total potential
CCN concentration.
k
¼
