Air quality expert group - Fine particulate matter (PM2.5) in ... - Defra

PM2.5/µgm -3
20
15
10
5
Roadside
0 5
12
hour
18 23
20
15
10
5
Concentrations and composition of PM2.5
Industrial
0 5
12
hour
18 23
Figure 3.3: Variation of PM2.5 concentrations (µg m -3 ) by hour of the day at
roadside (n=9) and industrial sites (n=4) in 2010. The shading represents the
95% confidence interval of the mean.
3.2.3 Diurnal variations at a site in Lisburn, Northern Ireland
8. Laxen et al. (2010) noted that the site in Lisburn, Northern Ireland, was
anomalous, showing much higher concentrations in 2009 that expected. This
anomaly was retained in 2010, with a much greater diurnal variation in PM2.5
concentrations (Figure 3.4). The range over the day is around five times greater
than at other urban background sites (cf. Figure 3.1). This is primarily due to
high overnight concentrations at this site, which peak at a similar time to the
peaks seen at other background sites (cf. Figure 3.2). It is suspected that these
high concentrations are due to domestic heating, which is still supplied in part
by solid fuel in Northern Ireland. This is supported by the observation that the
evening peak is much larger during the winter than the summer (not shown).
It is similar to the pattern for black carbon concentrations at Strabane (Figure
3.23), which has also been ascribed to domestic heating. The night-time peak
will also relate to the more stable atmospheric conditions at night, which will
enhance the impact of local emissions at this time. Clearly domestic solid
and/or liquid fuel used for domestic heating can be a significant source
of PM2.5, with black carbon being a major constituent. This source makes
its most significant contribution during the evening.
PM2.5/µgm -3
30
20
10
0 5
12
hour
18 23
30
20
10
J F M A M J
hour
J A S O N O
Figure 3.4: Variation of PM2.5 concentrations (µg m
49
-3 ) by hour of the day and
month of the year at the Lisburn site in Northern Ireland in 2010. The shading
represents the 95% confidence interval of the mean. Note the different scale to
the other figures.