Abstract
Abstract. There is limited availability of long-term, high temporal resolution, chemically speciated aerosol measurements which can provide further insight into the health and environmental impacts of particulate matter. The Monitor for AeRosols and Gases (MARGA, Applikon B.V., NL) allows for the characterisation of the inorganic components of PM10 and PM2.5 (NH4+, NO3-, SO42-, Cl-, Na+, K+, Ca2+, Mg2+) and inorganic reactive gases (NH3, SO2, HCl, HONO and HNO3) at hourly resolution. The following study presents 6.5 years (June 2006 to December 2012) of quasi-continuous observations of PM2.5 and PM10 using the MARGA at the UK EMEP supersite, Auchencorth Moss, SE Scotland. Auchencorth Moss was found to be representative of a remote European site with average total water soluble inorganic mass of PM2.5 of 3.82 μg m−3. Anthropogenically derived secondary inorganic aerosols (sum of NH4+, NO3- and nss-SO42−) were the dominating species (63 %) of PM2.5. In terms of equivalent concentrations, NH4+ provided the single largest contribution to PM2.5 fraction in all seasons. Sea salt was the main component (73 %) of the PMcoarse fraction (PM10-PM2.5), though NO3- was also found to make a relatively large contribution to the measured mass (17 %) providing evidence of considerable processing of sea salt in the coarse mode. There was on occasions evidence of aerosol from combustion events being transported to the site in 2012 as high K+ concentrations (deviating from the known ratio in sea salt) coincided with increases in black carbon at the site. Pollution events in PM10 (defined as concentrations > 12 μg m−3) were on average dominated by NH4+ and NO3-, where smaller loadings at the site tended to be dominated by sea salt. As with other western European sites, the charge balance of the inorganic components resolved were biased towards cations, suggesting the aerosol was basic or more likely that organic acids contributed to the charge balance. This study demonstrates the UK background atmospheric composition is primarily driven by meteorology with sea salt dominating air masses from the Atlantic Ocean and the Arctic, whereas secondary inorganic aerosols tended to dominate air masses from continental Europe.
Highlights
Gravimetric methods have long been used to monitor the long-term trends of the bulk aerosol mass contained in particulate matter (PM) with an aerodynamic diameter of less than 2.5 or 10 μm (i.e. PM2.5 and PM10); these generally provide no information on the chemical speciation of the aerosol
When compared with speciated PM2.5 measurements from a background site in the Midlands, UK (Harrison and Yin, 2010), Cl− concentrations were higher at Auchencorth Moss based on annual averages (Table 4) but are in a similar range to other UK sites (Abdalmogith and Harrison, 2006)
It is interesting that specific local events can be picked out from the data record, for example the maximum K+ concentration in 2012 of 2.61 μg m−3 occurred at 00:00 GMT on 6 November 2012 – Guy Fawkes or “fireworks“ night in the UK
Summary
Gravimetric methods have long been used to monitor the long-term trends of the bulk aerosol mass contained in particulate matter (PM) with an aerodynamic diameter of less than 2.5 or 10 μm (i.e. PM2.5 and PM10); these generally provide no information on the chemical speciation of the aerosol. In the current revised European Air Quality Framework Directive (Directive 2008/50/EC), countries are allowed to subtract significant “natural” contributions of aerosol from the total mass, if their contribution can clearly be quantified This is important for large “natural” pollution events, such as the long-range transport of Saharan dust which has been observed across Southern Europe and on occasions Northern Europe (Ansmann et al, 2003; Karanasiou et al, 2012). EMEP monitoring sites feed into the EMEP database which serves to underpin the organisation’s modelling and policy role to provide governments information on the deposition and concentration of air pollutants, and long-range transport of air pollutants (Tørseth et al, 2012; UNECE, 2004) He following study focuses on the first 6.5 years of data (1 June 2006 to 1 January 2013) from Auchencorth Moss, in conjunction with co-located measurements and air mass back trajectories. The trace gases measured concurrently with the aerosol composition and gas/aerosol partitioning are described in a companion paper (Twigg et al, 2015)
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