Polychlorinated Biphenyls (PCBs), and Polycyclic Aromatic Hydrocarbons (PAHs), in UK Air and Deposition.

Halsall, Crispin J (1995) Polychlorinated Biphenyls (PCBs), and Polycyclic Aromatic Hydrocarbons (PAHs), in UK Air and Deposition. PhD thesis, Lancaster University.

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Abstract

Air concentrations and deposition fluxes of PCBs and PAHs are presented for 1991 and 1992 at four UK urban centres (London, Manchester, Cardiff and Stevenge). Sampling was also carried out throughout 1993 at a rural location in NW England (Hazelrigg). This monitoring programme, part of the toxic organic micropollutants survey (TOMPS), has provided the first extensive data sets for PAHs and PCBs in the UK urban and rural atmosphere. Atmospheric PCBs and PAHs were sampled every other week at each of the sites using High-Volume air samplers, equipped with glass fibre filters to collect particulate and polyurethane foam plugs to serve as vapour adsorbents. Bulk deposition was collected every month. Furthermore, atmospheric PCBs were sampled every day at the rural site, between March and June 1994, in a preliminary attempt to investigate the influence of separate meteorological episodes. At the four urban sites mean annual SigmaPAH concentrations ranged from approximately 60 - 150 ng m-3, while the mean SigmaPCB concentration ranged from 500 - 1500 pg m-3. These concentrations are the same order of magnitude as contemporary concentrations reported in other urban areas on an international basis. The lighter, predominantly vapour phase PAHs of fluorene and phenanthrene and the lower chlorinated PCB congeners, 28 and 52, dominate the atmospheric profile for both sets of compounds respectively. SigmaPAH concentrations were actually greater in the Hazelrigg atmosphere (~ factor 2) than in Manchester. This was due to significantly higher concentrations of fluorene and phenanthrene. This site and another rural site in the NW England are under the influence of local sources. Added to this, volatilisation of these lighter compounds from secondary sources such as sediments/soils/vegetation may explain the elevated concentrations during the warmer summer months. Principal components analysis highlighted the dominance of these lighter compounds in the rural atmosphere over the urban atmospheres. At Hazelrigg the SigmaPCB concentrations were lower than the urban sites by a factor of between 3-4, reflecting the lack of point sources in the rural environment. Seasonal variations were evident for the heavier PAH in both the urban and rural atmosphere. This was characterised by elevated concentrations in the winter, possibly due to increased fuel consumption for residential heating. The lighter compounds in the urban atmosphere did not show the seasonal cycling evident in the rural atmosphere, probably due to the masking effect of increased primary emissions in the winter. The SigmaPCB concentrations showed elevated concentrations in the summer at all of the sites, the vapour phase concentrations of several prominent congeners being correlated with temperature. The more chlorinated congeners showed an increased cycling amplitude from winter to summer than the less chlorinated congeners. This may be due to them being more readily exchangeable between surfaces and the atmosphere, than the lower chlorinated congeners. Partitioning between the particulate and vapour phases for the PAHs and the PCBs appears to be controlled mainly by temperature and a compound's volatility. Total suspended particulate plays a lesser role, the partitioning behaviour (calculated partition coefficients at 20°C) for six indicator congeners being similar in both the Manchester and Hazelrigg atmospheres. As surface area available for sorption is more important than just particulate concentration it is postulated here that the amount of area available at the earth's surface, particularly if covered by vegetation, will play a more important role in vapour phase sorption/desorption than atmospheric particulate. Meteorological episodes typified by high pressure anti-cyclonic systems resulted in elevated particulate phase SigmaPCB and SigmaPAH concentrations in the Cardiff and Manchester atmospheres respectively. The use of air mass back trajectories identified three separate air masses at the Hazelrigg site, when SigmaPCB concentrations varied significantly from the sampling mean. The lack of profile differences between these air masses (originating from different areas) indicate similar sources to the atmosphere, or similar processes that occur during transport that result in a uniform profile. The mean sPAH deposition flux varied from ~5 ug m-2 d-1 at the urban sites to ~2 ug m d-1 at the rural site. The mean SigmaPCB deposition flux varied from ~0. 8 ng m-2 d-1 at the urban sites to ~0. 2 ng m-2 d-1 at the rural site. Comparison with fluxes reported at rural/remote sites in north America would suggest that Hazelrigg and a site in the Lake District in NW England represent semi-urban areas; it seems that greater distances away from urban centres are required before 'true' rural fluxes are obtained. (Abstract shortened by ProQuest.).