Chemistry Reference
In-Depth Information
in the GAA, a significant portion of NO
3
(about 30%) was found in fine mode,
indicating ammonium nitrate formation mainly for the winter period.
By comparing the NO
3
levels in PM
10
, the difference between GAA and FKL
minimised during the warm season (2.1 and 1.8
gm
3
, respectively). On the other
hand, local anthropogenic sources within the GAA dominate during the cold season
as for PM
10
the GAA/FKL ratio is reaching values up to 2. Similar trend also
existed for NO
3
in the PM
1
fraction. However, the GAA/FKL ratio during winter
was much pronounced and reached values as high as 8 that is almost double the
factor of 4-5 during the warm season. This observation is in agreement with
ammonium nitrate formation in the GAA during winter.
m
5.5.2 Secondary Organic Aerosol
Grivas et al. [
62
] were the first to report continuous measurements of EC and OC, at
an urban location in central Athens, Greece, for an 8-month period (January-August).
Average concentrations of 2.2
gC m
3
were observed, for EC and
OC, respectively. The contribution of carbonaceous compounds (EC plus organic
matter) to PM
10
was calculated at 26% in agreement with previous estimates [
21
,
63
].
The seasonal variability of EC was found to be limited, while OC mean
concentrations were significantly higher (by 23%), during the warm months
(May-August). EC and OC produced a bimodal diurnal cycle, with the morning
rush hour traffic mode prevailing. However, midday-to-afternoon presence of sec-
ondary organic aerosol (SOA) was strongly indicated. The temporal variation of EC,
OC and their correlation patterns with primary and secondary gaseous pollutants,
suggested that, although primary emissions affected both fractions, SOA formation is
an important factor to be accounted for, especially during the photochemical season.
Secondary organic carbon was estimated using the EC tracer method and orthogonal
regression on OC, EC hourly concentration data. The average contributions of
secondary organic carbon (SOC) to OC were calculated at 20.9% for the cold period
and 30.3% for the warm period. The SOC diurnal variations suggested photochemical
formation throughout the year, intensified during summer months, with the correla-
tion coefficient between SOC and the sum of oxidants (NO
2
+O
3
)reachingupto
0.84.
Theodosi et al. [
64
] studied the spatial variability of carbonaceous aerosols along
several locations around the Eastern Mediterranean, including big cities (Athens
and Istanbul), urban background (Sinop, Erdemli), rural background (Aegina and
Penteli) and regional background sites (Gokceada and Finokalia, Fig.
7
). In this
work the concentration of SOC was estimated from the following equation:
gC m
3
and 6.8
m
m
SOC
¼
OC
total
ð
OC
=
EC
Þ
minimum
EC
(1)
By using an OC/EC minimum ratio of 0.3-0.4 suggested by Pio et al. [
65
] and
based on the tunnel studies, SOC percentage contribution can be estimated for all
