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

PM2.5 in the UK
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12. Results are also available for two sites using FDMS monitors, although only
covering a period of five years (Figure 3.7). There is no significant trend at
either site over this short period (95% confidence level in a Mann–Kendall
trend analysis). The limited evidence available, including that for sulphate
and nitrate in Figure 3.20, is suggestive, but no more, of a slight overall
downward trend in PM2.5 over the last decade.
PM 2.5
30
25
20
15
10
5
Swansea Roadside
2007 2007 2008 2008 2009
Year
2009 2010 2010 2011 2011
Auchencorth Moss
(Rural)
2007 2007 2008 2008 2009
2009 2010 2010 2011 2011
Figure 3.7: PM2.5 concentrations (FDMS, µg m -3 ), 2006-2011, at Swansea roadside
site in Wales and Auchencorth Moss rural site in Scotland. A smoothed trendline
has been fitted with the shading representing the 95% confidence interval.
3.4 Relationship of PM2.5 with other pollutants
3.4.1 Relationship of PM2.5 with PM10
13. Laxen et al. (2010) examined the ratios of PM2.5 to PM10 in 2009 and identified
an overall decline in the ratios with distance from Dover in the south-east corner
of England. The data have been examined again for 2010 and show a similar
pattern, even though there were fewer sites with valid data (and a different
set of sites), 16 in 2010, compared to 19 in 2009 (Figure 3.8). The ratios have
been calculated as the ratio of the average concentration of PM2.5 to the
average concentration of PM10 for those hours when data were available for
both measures. They were considered valid if the ratio was based on more than
75% of the hours in the year. For both years the ratio declines with increasing
distance from the south-east of England. This is consistent with the more
significant contribution of secondary PM in the south-east, with this secondary
PM being more significant in the PM2.5 fraction.
Year