Chemistry Reference
In-Depth Information
Particulate Matter < 1 µm (PM
1
)
40
30
20
10
0
Organic Carbon
12
8
4
0
Levoglucosan
0.4
0.3
0.2
0.1
0.0
Date
Fig. 2 Daily average concentrations of PM
1
, organic carbon, and levoglucosan at an urban
background site in Helsinki from March 2006 to February 2007. The elevated concentrations in
April to May and in August are due to wildfires. The increase in levoglucosan concentrations
during fall and winter is caused by wood burning in domestic heating
2006 at Spitsbergen, the particle number concentrations were about ten times larger
during the plume than usually at that time of year [
10
].
The increase in the number concentration is more pronounced for larger
particles. In general, particle number concentration increases for the accumulation
mode particles (diameter of 0.1-1
m) but a decrease of nucleation and Aitken
m
mode particles (
100 nm in diameter) has been observed during the LRT smoke
episodes. For example in Hyytiala in spring 2002, the particle number concentra-
tion increased during the smoke episode by a factor of 5.6 in the accumulation
mode, decreased slightly in the Aitken mode, and decreased strongly in the nucle-
ation mode [
12
]. The disappearance of the smallest particles could be due to the
condensation of gas-phase components on the larger particles that were abundant in
smoke plume. Therefore gas-to-particle conversion could not form new particles
during the smoke events. The same behavior was detected in spring 2006 at
Spitsbergen where nucleation and small Aitken mode particles were almost
completely suppressed [
27
] during the smokes.
Besides the growth in the number concentration, also the particle size distribu-
tion changes during the smoke episodes. In Kuopio 2010, the diameter of the
aerosol particles was twice as large during the smoke event as it was in the
background conditions [
33
]. In normal conditions the peak of the size distribution
was at 55 nm but during the smoke the peak shifted to 186 nm. The increase in the
<
