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

PM2.5
25
25
12
5
15
10
NO1 20
10
5
PM2.5
0 5
12 18 23
NO1
Concentrations and composition of PM2.5
0 5
12 18 23 0 5
12 18 23
hour hour
20
15
10
PM10 25
5
20
15
NO2 25
10
5
PM10
0 5
12 18 23
Figure 3.9: Variation of PM2.5, PM10, NOx and NO2 concentrations (µg m -3 ) by
hour of the day at eight urban background sites across the UK in 2010.
The shading represents the 95% confidence interval of the mean. Note the
different scales.
3.5 Spatial patterns
3.5.1 Spatial homogeneity of PM2.5 hourly mean concentrations
20. Laxen et al. (2010) reported a high level of spatial homogeneity of hourly
mean PM2.5 concentrations across sites in southern England, from Oxford
through to Southend. They derived correlation coefficients for paired data sets
from 11 sites and plotted the results as a function of distance between the
sites (see Figure 3.10). Hourly mean concentrations for sites within 20 km of
each other are highly correlated (correlation coefficient > 0.8). The correlation
then declines with distance, but is still high at 100 km separation (correlation
coefficient ~0.7). The high level of spatial homogeneity is consistent with
PM2.5 being dominated by regional sources, including secondary PM,
with local sources being less important, but will also reflect the strong
seasonal pattern linked to greater winter emissions and more stable
atmospheric conditions.
NO2
55