M.E. Goldstone

A review of atmospheric polycyclic aromatic hydrocarbons: Sources, fate and behavior

A review has been written to assess the sources, fate and behavior of polycyclic aromatic hydrocarbons (PAH) in the atmosphere. PAH are formed mainly by anthropogenic processes, especially the combustion of organic fuels. PAH concentration in air will reflect the location of source emitters, with high concentrations corresponding with urban and industrial areas. PAH are however ubiquitous contaminants of the environment having been detected in remote areas of the world. This is thought to be due to long term transport in the atmosphere. PAH can also be subjected to chemical and/ or photochemical change whilst resident in the atmosphere prior to their removal by either wet or dry deposition.

Analysis and interpretation of air quality data from an urban roadside location in Central London over the period from July 1991 to July 1992

Abstract Air quality data from a one year study at an urban roadside location in Central London are reported for a large number of both organic and inorganic air pollutants. The location is 5 m from the kerbside of a moderately busy road, Exhibition Road, enclosed on each side by buildings. The pollutants measured included NO, NO2, O3, SO2, CO and CO2. together with 28 non-methane hydrocarbons, including measurements of the air toxics: benzene and 1,3-butadiene. The interpretation of the air quality data used simple statistical techniques, including principal components analysis, and air pollution models of the Gaussian plume and box model variety. A comprehensive validation of the published emission inventory estimates for London was attempted using the observed air quality data. Separate contributions from the local traffic on Exhibition Road, from the general traffic in Central London, natural gas leakage and fuel combustion have been identified. The agreement between the emission factors required to explain the observed concentrations and those in the literature was excellent for a number of air pollutants and these should be of value in environmental impact assessments. Attention was also directed to an intense wintertime pollution episode which occurred during the study period, when the concentrations of all pollutants were considerably higher than usual. Elevated nitrogen dioxide concentrations were a significant feature of this episode and the box model was used to ascertain its likely production mechanism. A relationship between the hourly mean nitrogen dioxide and NOx concentrations was defined which should have general applicability in air quality policy assessments.

Phase distribution and particle size dependency of polycyclic aromatic hydrocarbons in the urban atmosphere

Abstract Distributional characteristics of polycyclic aromatic hydrocarbons in urban air were investigated with respect to gas-particle partitioning and dependency on particle size. The relationship between the gas particle distributions of PAH and ambient temperature was described using the Langmuir adsorption concept, while the particle size dependency was demonstrated based on a Lundgren type mass distribution.

Concentrations of particulate and gaseous polycyclic aromatic hydrocarbons in London air following a reduction in the lead content of petrol in the United Kingdom.

The environmental importance of tropospheric polycyclic aromatic hydrocarbons (PAH) is reviewed. The impact of reducing lead on airborne PAH is indicated and the importance of monitoring both particulate and gaseous-phase PAH is demonstrated. A Brief description of a sampling regime performed from 1985 to 1987 is given. Sampling of 18 PAH was performed and particulate lead concentrations at the kerbside were measured concurrently. Measurements indicate that there is a pronounced seasonality in PAH concentrations and in the distribution of PAH between particulate and gaseous phases. On average, 47% of the PAH measured were in the gaseous phase, indicating the importance of measuring the volatile fraction. The dominance of the common variation of each PAH was also investigated using principal components analysis. An uneven spread of data prior to and following the reduction in lead content, hindered a thorough examination of the effect of this change on PAH concentrations. However, they appeared to indicate only a small change in PAH concentration and this was linked to an increase in aromatic content of the petrol, which was much less than expected.

The sources and behaviour of tropospheric anthropogenic volatile hydrocarbons

Abstract A review of literature regarding tropospheric anthropogenic volatile hydrocarbons is undertaken in order to assess trends in concentrations and the behaviour of these compounds in the troposphere. The impact of control legislation on vehicle emission levels is discussed. The volatile hydrocarbon composition of ambient air will usually reflect the location of sources, with high concentrations corresponding with urban and industrial areas. Once present in air volatile hydrocarbons perform important roles in oxidant and secondary aerosol formation. The impact upon the health of humans from exposure to tropospheric volatile hydrocarbons, especially aromatic compounds, is also an area of great importance. Volatile hydrocarbons are removed from tropospheric circulation by reaction and deposition processes.

Polycyclic aromatic hydrocarbons in central London air during 1991 and 1992

The results of monitoring for 18 polycyclic aromatic hydrocarbons (PAH) at Exhibition Road, London, UK during the period from January 1991 to September 1992 are presented. Although both particulate and gaseous PAH were analysed, the results are expressed as total PAH. The PAH measurements are complemented by the simultaneous monitoring of a range of air quality variables. These parameters have been subjected to correlation analysis and the dependence on motor vehicle emissions for many of the PAH species is inferred. The majority of the PAH displayed higher annual mean concentrations during 1991 than previous measurements taken at the same site in 1987. The impact of motor vehicle emission legislation, the increased use of unleaded petrol and the rise in the use of diesel powered motor vehicles are all discussed in the context of the presented results. A pollution event during December 1991 caused significantly increased PAH concentrations. A comparison with PAH data from another site in London indicates good agreement between the two sets of data.

The behaviour of heavy metals during wastewater treatment. I. Cadmium, chromium and copper.

Abstract Mechanisms of metal removal during sewage treatment are reviewed and the application of these mechanisms to cadmium, chromium and copper removals are discussed. Sampling was performed at Whitlingham sewage treatment works (Anglian Water), Norwich, to assess the removal mechanisms of these metals, with reference to partitioning between particulate and soluble phases. Mass balances were performed as a means of quality control. It was concluded that the metals were primarily associated with suspended solids. However, considerable solubilization of cadmium and copper occurred during activated sludge treatment, possibly due to the addition of anaerobic solids in the overflow from a waste activated sludge consolidation tank. Chromium was not affected in a similar manner, possibly due to a change in its valency state.

The behaviour of heavy metals during wastewater treatment. III, Mercury and arsenic

Abstract The removal mechanisms of mercury and arsenic during sewage treatment are reviewed and possible biotransformations of mercury are discussed. Sampling was performed at Whitlingham sewage treatment works (Anglian Water), Norwich. Removal mechanisms were assessed with reference to partitioning between particulate and soluble phases. Further sampling and analysis was performed to determine the importance of mercury methylation. It was concluded that mercury behaved differently in the two studies, possibly due to a change in crude sewage speciation and the introduction of a picket fence thickener in the waste activated sludge consolidation tank. In situ methylation of mercury was found, especially in the presence of bacterial solids. Arsenic removals during primary sedimentation were very high, with soluble and particulate removals on a similar level. Paradoxically arsenic removals during activated sludge treatment were extremely low.

Methodological aspects of measuring polycyclic aromatic hydrocarbons in the urban atmosphere

Abstract The environmental importance of atmospheric polycyclic aromatic hydrocarbons (PAH) is briefly discussed. A sampling regime, using filters and Tenax TA adsorbent, is outlined which enables the collection of 18 PAH in air, from both the particulate and gaseous phases. An extraction and clean up process is described, which prepares the sample for reversed phase high performance liquid chromatography (HPLC) by transferring the analyte to acetonitrile. Tests on the overall methodology indicate that the procedure provides a sensitive and accurate method for assessing levels of atmospheric PAH. An examination of the differing sampling efficiency between impaction and filtration was undertaken, which indicated the effect of sampling duration and temperature on sample integrity. Evidence of the impact of other gaseous pollutants on measured PAH concentrations was highlighted by stepwise multiple regression.

The behaviour of heavy metals during wastewater treatment II. Lead, nickel and zinc

Abstract Mechanisms of metal removal during sewage treatment are reviewed and the application of these mechanisms to lead, nickel and zinc removals are discussed. Sampling was performed at Whitlingham sewage treatment works (Anglian Water), Norwich, to assess the removal mechanisms of these metals, with reference to partitioning between particulate and soluble phases. Mass balances were performed as a means of quality control. It was concluded that lead was primarily associated with solids. However, it was solubilized during activated sludge treatment and this was possibly due to the addition of anaerobic solids in the overflow from a waste activated sludge consolidation tank. The soluble phases of nickel and zinc were not significantly affected by any of the processes in the works.