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Trends

Particulate Matter (measured as PM10)

This pollutant is of great interest because many studies have linked it with human health effects, and because scientists do not believe that there is a "safe" threshold concentration, below which no effects on human health would be expected to occur.

Historically many of Northern Ireland's monitoring sites used the Tapered Element Oscillating Microbalance (TEOM) to monitor PM 10. The TEOM has a relatively high operating temperature; this is necessary to prevent condensation on the filter, but can cause evaporation of the volatile component of the particulate matter collected. Measurements made using a TEOM therefore need to be corrected for this. For years up to 2008 the convention was to apply a factor of 1.3 to the data, and the data presented here for those years have been adjusted in this way. TEOM data from 1st Jan 2008 onwards have been adjusted for possible loss of the volatile component using the King's College Volatile Correction Model (VCM) page. This method takes measurements from FDMS-TEOM monitors located elsewhere in the region, (which measure both the volatile and non-volatile fraction), and uses these to apply a correction to the daily or hourly dataset. This is the recommended method for correcting TEOM data after 2008, and in order to analyse long-term trends a VCM correction has been carried out for the TEOM data presented here for years 2008 onwards. The data that have been VCM-corrected are as follows:

  • Armagh Lonsdale Road: from 1st Jan 2009 until the TEOM was upgraded to an FDMS on 1st Oct 2010.
  • Belfast Centre: 11th Mar 2008 until the TEOM was upgraded to an FDMS on 1st Oct 2008.
  • Belfast Stockman’s Lane: from 1st Jan 2008 until the TEOM was upgraded to an FDMS on 1st Mar 2009.
  • Derry Brooke Park: none (upgraded to FDMS in early 2008).
  • Lisburn Dunmurry Seymour Hill: from 1st September 2014 onwards (this site previously had an FDMS from its start-up in 2012).
  • Lough Navar: from 1st Jan 2008 until the TEOM was upgraded to an FDMS on 16th May 2009.
  • North Down Holywood A2: from 1st Jan 2008 to date (the PM10 monitor at this site is still an unmodified TEOM).
  • Newry Canal Street: from when the site started monitoring on 1st June 2009 to date (this PM10 monitor is also still an unmodified TEOM).
  • Newry Monaghan Row: 1st Jan 2008 until the TEOM was upgraded to an FDMS on 7th Mar 2008.
  • Newry Trevor Hill: 1st Jan 2008 until the TEOM was upgraded to an FDMS on 28th Mar 2008.
  • Strabane Springhill Park: none: this site has a Beta Attenuation Monitor which does not require correction.

PM10 at Urban Background Sites

A smoothed trend plot of de-seasonalised monthly mean PM 10 concentrations at the longest-running urban background site in Northern Ireland, Belfast Centre, is shown in Figure 3. This shows a general decrease between 1992 (when the site began monitoring PM10) and 2014. There is a slight increase in 2010: this is likely to be due to cold winter weather in this year, which caused periods of elevated particulate pollution.

Figure 3: Smoothed Trend Plot for PM10 at Belfast Centre, 1992-2016
(clicking on the graph will open a larger image in a new window)

Figure 4 quantifies the downward trends in PM 10 pollution measured at four urban background sites and one rural background site, all of which have been monitoring this pollutant since 2003 or earlier. The urban background sites are: Belfast Centre, Derry Brooke Park, Newry Monaghan Row and Strabane Springhill Park. The rural background site is Lough Navar. All these non-roadside sites show significant downward trends in PM10 concentration over this 12-year period - though the trend is not consistent in all cases, for example Strabane Springhill Park’s plot is largely flat after a large decrease around 2005. (The pattern at Strabane Springhill is similar to that for SO2).

The four urban background sites show a clear peak around the end of 2010, likely to be due to the cold weather at that time.

Figure 4 : De-seasonalised Trend Plots for PM10 at Five Long-Running Background Sites, 2002-2016
(clicking on the graph will open a larger image in a new window)

PM10 at Traffic-Related Urban Sites

Figure 5 shows trends in PM 10 at four long-running urban traffic-related PM10 monitoring sites in Northern Ireland: Armagh Lonsdale Road, Belfast Stockman’s Lane, Newry Trevor Hill and North Down Holywood A2.

Figure 5: De-seasonalised Trend Plots for PM10 at Four Long-Running Urban Traffic Sites, 2005-2016
(clicking on the graph will open a larger image in a new window)

Like the background urban sites discussed above, some of these roadside sites also clearly show the winter peak in late 2010, due to the cold winter weather in that year.