Chemistry Reference
In-Depth Information
Fig. 3 Box plot of EC
wb
,OC
wb
and PM
wb
from rural and urban background sites measured in
PM10 and PM2.5.
Red line
: median, edges of the box are the 25th and 75th percentiles, whiskers
extend to the most extreme data points not considered as outliers, outliers are plotted individually
widespread use of wood for residential heating in the Alpine region, often burnt in
small stoves or fireplaces at poor operating conditions. It is clear from the absolute
contributions of wood burning emissions to the particulate air pollutants as shown
in Fig.
3
that wood burning is during wintertime a major and probably at many rural
sites dominating source of ambient particulate matter and carbonaceous aerosols.
3.2.5 Diurnal Variations of Elemental Carbon from Wood Burning
Emissions from wood burning vary strongly during the course of the day. The
analysis of data from an aerosol mass spectrometer and from an aethalometer is
capable of providing source contributions with sufficient temporal resolution to
resolve diurnal variation of source contributions. Recent publications show that the
highest concentrations of wood burning constituents occur primarily during evening
hours, wood burning-related evening peak contributions were found to occur later
than the traffic-related evening peaks [
9
,
45
-
47
].
Here we present diurnal variations of EC
WB
with exemplary data from the Swiss
stations Payerne, Magadino and Zurich. The contribution of WB to EC
WB
was
obtained from continuous optical absorption measurements at several wavelengths
during wintertime (December 2010 to February 2011), the data analysis was
performed as described in detail by Herich et al. [
45
]. The resulting diurnal cycles
of EC
WB
in Payerne, Magadino and Zurich are shown in Fig.
4
, the results are
separately shown for weekdays and weekends. The diurnal variations are similar at
all three locations. Apart from the prominent evening peak, concentrations are
slightly enhanced prior to noon. Lowest concentrations occur during the afternoon.
The diurnal variations are for weekdays and weekends very similar. For all stations
daily minimum and maximum concentrations differ by a factor of about 2-3.
The enhanced concentrations in the evening may to some extent occur due to
meteorological conditions, e.g. a lower mixing layer height can limit dilution
processes during the night.
