Anja Tremper, Ranjeet S Sokhi, Lakhu Luhana and Agneta Burton

1. Summary

Size fractionated aerosol have been sampled using a Grasbey Andersen Impactor at an urban background site at the University Campus during the summer of 1997. The samples were collected for eight size ranges during three separate run s. The samples were analysed gravimetrically for aerosol mass and physically characterised using a Scanning Electron Microscopy (SEM) which provided information on the shape and size of the particles along with some elemental information using electron m icroprobe analysis (EMPA). Atomic Absorption Spectrometry (AAS) has been employed to analyse the particles for Cd, Cu, Fe, Pb and Zn for each size fraction.

2. Aim of research

The overall aim is to investigate temporal variation of fine particulates in urban and roadside sites. This will enable contributions from urban background and traffic sources to be quantified in relation to mass, size and chemical composition. This information is essential in order to understand better processes responsible for dispersion of aerosols in the urban atmosphere.

3. Activities during the year

1. Three runs of size differentiated particle sampling was conducted at an urban background site during a summer period (1997).
2. Mass loading according to particle size has been investigated during this sampling period.
3. The particles have been examined with a Scanning Electron Microscope (SEM) to provide information on the shape and on their chemical composition.
4. Trace metal analysis has been performed for the following elements Cd, Cu, Fe, Pb and Zn for each of the stages.
5. Collaboration with other Principal Investigators such as Drs Laszlo Bozo (Hungarian Meteorological Service) and Jaakko Kukkonen (Finnish Meteorological Institute) is being explored for a comprehensive European programme.
6. Results have been presented at the SATURN Annual Conference in Hamburg (1998).

4. Principal Results

SEM analysis has shown a wide variety of physical characteristics that in general depend on the size of the particle. A typical ‘large’ particle is shown in Figure 1 whereas smaller particles tend to agglomerate into ‘chainlike’ str uctures. EMPA revealed that the coarse fraction consisted mainly of Na and Cl in addition to Fe and the finer fractions tended to consist of sulphur compounds. This confirms the observations reported by other studies (Zou and Hooper 1997 and Luhana 1995). Results indicate that mass loading in general increase with decreasing particle size for the range investigated but this would also be critically dependent upon source distribution and meteorological conditions. For one of runs, Figure 2, no trend in mas s loading was observed as a function of size. This will need to be investigated further in relation to sources and meteorological parameters. Metal analysis indicates a large proportion of iron for the larger particles (shown in Figure 3). The results als o indicate that proportion of Pb and Zn increases for the finer fractions. Similar concentration of metals and mass has been observed at other UK sites (QUARG 1996).

5. Main conclusions

In general there was a gradual increase of the mean mass load of particulate matter with decreasing aerodynamic size range. Metals such as Zn and especially Pb are associated with fine fractions of PM10. SEM analysis shows marked di fferences in the morphology of the particles as a function of their size. The investigations in the chemical composition of PM10 suggest that the values of metal concentrations measured at this site are comparable with other similar sites in the UK.

6. Aim of the coming year

A common aim will be to establish collaborative programmes with other Principal Investigators within SATURN. This will provide wide and comprehensive coverage of particle measurements and will facilitate European scale comparisons i n relation to source distributions and apportionment. Furthermore, a new sampling station is being established at the University of Hertfordshire which will enable very detailed sampling and measurements to be made at background and roadside sites. Specif ic objectives will include:

To conduct sampling campaign at an urban background site for mass and number analysis of size fractionated aerosol using MOUDI, TEOM, Partisol and GRIMM.

To carry out elemental and ionic compassion of size differentiated particulates using AAS, ICP and Ion Chromatography.

To establish a common protocol in order to conduct European campaigns and comparisons.

Luhana L 1995,

Source Apportionment of Particulate matter over Birmingham Using Receptor Modelling, University of Birmingham, UK

QUARG 1996

Airborne Particulate Matter in the United Kingdom, Quality of Urban Air Review Group, Department of Environment, UK

Zou L Y and Hooper M A 1997

Size resolved airborne particles and their morphology in central Jakarta. Atmos. Environ. 31(8), 1167-1172.

Figure 1. Soot particle sampled with an ambient air particle sampler and identified with a Scanning Electron Microscope

Figure 2. Distribution of the mass loadings over the size ranges

Figure 3. Trace metal analysis of PM10 at Hatfield site.