UK Atmosphere Research Articles

Impacts of the 2014–2015 Holuhraun eruption on the UK atmosphere

Abstract. Volcanic emissions, specifically from Iceland, pose a pan-European risk and are on the UK National Risk Register due to potential impacts on aviation, public health, agriculture, the environment and the economy, from both effusive and explosive activity. During the 2014–2015 fissure eruption at Holuhraun in Iceland, the UK atmosphere was significantly perturbed. This study focuses one major incursion in September 2014, affecting the surface concentrations of both aerosols and gases across the UK, with sites in Scotland experiencing the highest sulfur dioxide (SO2) concentrations. The perturbation event observed was confirmed to originate from the fissure eruption using satellite data from GOME2B and the chemical transport model, EMEP4UK, which was used to establish the spatial distribution of the plume over the UK during the event of interest. At the two UK European Monitoring and Evaluation Program (EMEP) supersite observatories (Auchencorth Moss, SE Scotland, and Harwell, SE England) significant alterations in sulfate (SO42−) content of PM10 and PM2.5 during this event, concurrently with evidence of an increase in ultrafine aerosol most likely due to nucleation and growth of aerosol within the plume, were observed. At Auchencorth Moss, higher hydrochloric acid (HCl) concentrations during the September event (max = 1.21 µg m−3, cf. annual average 0.12 µg m−3 in 2013), were assessed to be due to acid displacement of chloride (Cl−) from sea salt (NaCl) to form HCl gas rather than due to primary emissions of HCl from Holuhraun. The gas and aerosol partitioning at Auchencorth Moss of inorganic species by thermodynamic modelling confirmed the observed partitioning of HCl. Using the data from the chemical thermodynamic model, ISORROPIA-II, there is evidence that the background aerosol, which is typically basic at this site, became acidic with an estimated pH of 3.8 during the peak of the event.Volcano plume episodes were periodically observed by the majority of the UK air quality monitoring networks during the first 4 months of the eruption (August–December 2014), at both hourly and monthly resolution. In the low-resolution networks, which provide monthly SO2 averages, concentrations were found to be significantly elevated at remote “clean” sites in NE Scotland and SW England, with record-high SO2 concentrations for some sites in September 2014. For sites which are regularly influenced by anthropogenic emissions, taking into account the underlying trends, the eruption led to statistically unremarkable SO2 concentrations (return probabilities > 0.1, ∼ 10 months). However, for a few sites, SO2 concentrations were clearly much higher than has been previously observed (return probability < 0.005, > 3000 months). The Holuhraun Icelandic eruption has resulted in a unique study providing direct evidence of atmospheric chemistry perturbation of both gases and aerosols in the UK background atmosphere. The measurements can be used to both challenge and verify existing atmospheric chemistry of volcano plumes, especially those originating from effusive eruptions, which have been underexplored due to limited observations available in the literature. If all European data sets were collated this would allow improved model verification and risk assessments for future volcanic eruptions of this type.

Gaseous chemistry and aerosol mechanism developments for version 3.5.1 of the online regional model, WRF-Chem

Abstract. We have made a number of developments to the Weather, Research and Forecasting model coupled with Chemistry (WRF-Chem), with the aim of improving model prediction of trace atmospheric gas-phase chemical and aerosol composition, and of interactions between air quality and weather. A reduced form of the Common Reactive Intermediates gas-phase chemical mechanism (CRIv2-R5) has been added, using the Kinetic Pre-Processor (KPP) interface, to enable more explicit simulation of VOC degradation. N2O5 heterogeneous chemistry has been added to the existing sectional MOSAIC aerosol module, and coupled to both the CRIv2-R5 and existing CBM-Z gas-phase schemes. Modifications have also been made to the sea-spray aerosol emission representation, allowing the inclusion of primary organic material in sea-spray aerosol. We have worked on the European domain, with a particular focus on making the model suitable for the study of nighttime chemistry and oxidation by the nitrate radical in the UK atmosphere. Driven by appropriate emissions, wind fields and chemical boundary conditions, implementation of the different developments are illustrated, using a modified version of WRF-Chem 3.4.1, in order to demonstrate the impact that these changes have in the Northwest European domain. These developments are publicly available in WRF-Chem from version 3.5.1 onwards.

Atmospheric polybrominated diphenyl ethers (PBDEs) in the United Kingdom

The occurrence of PBDEs has been studied in the atmosphere of four sites in the United Kingdom over a period of ten years. The concentrations have exhibited a sharp decrease after 2001–2003. This is evident in the urban sites of Manchester and London and at the semi-rural site of Hazelrigg. The average ΣPBDE half-lives for these three sites were 3.4, 2.0 and 3.5 years respectively. ΣPBDEs concentrations in the UK (in 2010 ΣPBDEs < 10 pg m−3) are among the lowest reported in literature. Comparison of concentrations to estimated emissions and employment of PBDE profiles suggest that PBDEs in the UK atmosphere originate from primary emissions from products that contain mainly the penta-BDE technical mixture. The detection of BDE-183 in the majority of samples hints that octa-bromodiphenylether has also been used extensively in the UK, however to a smaller extent than the penta- product.

Processes affecting concentrations of fine particulate matter (PM2.5) in the UK atmosphere

PM2.5 is now subject to a limit value and exposure-reduction targets across the European Union. This has led to a rapid expansion in PM2.5 monitoring across Europe and this paper reviews data collected in the United Kingdom in 2009. The expected gradient between rural, urban background and roadside sites is observed, although the roadside increment is generally rather small except for heavily trafficked street canyon locations. PM2.5:PM10 ratios decline from around 0.8 in southeast England to below 0.6 in Scotland consistent with a higher contribution of secondary particulate matter in southeast England. Average diurnal profiles of PM2.5 differ around the UK but have a common feature in a nocturnal minimum and a peak during the morning rush hour. Central and southern UK sites also show an evening peak following a concentration reduction during the mid afternoon which is not seen at northern UK sites and is attributed to evaporation of semi-volatile components, particularly ammonium nitrate. Concentrations of PM2.5 are typically highest in the winter months and lowest in the mid-summer consistent with better mixing and volatilisation of semi-volatile components in the warmer months of the year. Directional analysis shows a stronger association of PM2.5 with easterly winds associated with air masses from the European mainland than with the direction of local traffic sources.

Properties of coarse particles in the atmosphere of the United Kingdom

Abstract The recent rapid expansion of PM2.5 monitoring alongside PM10 has allowed estimation of concentrations of coarse particles (PM2.5–10) by difference. This has been carried out for sites using comparable measurement techniques for both metrics, and the properties of the hourly average concentration data have been evaluated. In the UK atmosphere, coarse particles generally represent well under half of PM10 mass. The ratio of PMcoarse to PM10 averages 0.29 ± 0.14 (n = 43) for FDMS measurements and 0.38 ± 0.30 (n = 12) for TEOM measurements and does not show a very consistent pattern according to site type. The values are mostly higher for TEOM measurements than for FDMS which is explicable in terms of semi-volatile losses predominantly from fine particles in the TEOM. Sites where PMcoarse/PM10 exceeds 0.5 generally have a marine or industrial influence. Correlations between hourly PM2.5 and PM10 are generally very high (mean R = 0.80 for FDMS data and mean R = 0.85 for TEOM data) whilst those between PMcoarse and PM2.5 are very much lower (mean R = 0.09 for FDMS measurements and mean R = 0.41 for TEOM measurement sites). When inter-site correlations are examined between sites of similar characteristics within 30 km of one another, the inter-site correlation of PM2.5 (R = 0.56–0.87) is very much higher than that of PMcoarse (R = 0.25–0.60). Coefficients of Divergence indicate lower spatial homogeneity for PMcoarse than for PM2.5. When hourly data are used to construct pollution roses, it is typical for PM2.5 and PM10 to show a similar pattern dominated either by long-range transport or local traffic sources while PMcoarse can show quite a different pattern indicative of a different range of contributory sources. Plots of particle concentration versus wind speed show a monotonic decline of concentration with increasing wind speed for PM2.5, but an initial decline and an increase at higher wind speeds for PMcoarse. There are relatively few datasets allowing an examination of temporal trend but those available for 4.5–10 years generally show no significant trend with time for fine or coarse particles, or for PM10. Weekday/weekend and diurnal concentration patterns for coarse and fine particles show a strong anthropogenic influence on PMcoarse and a larger weekday/weekend difference for PMcoarse than PM2.5. It is concluded that coarse and fine particles show very different behaviour as a result of their different sources and properties. The lower spatial homogeneity of coarse particles may be a contributory factor in why they appear to be less toxic than fine particles in epidemiological studies.

Temporal Trends and Controlling Factors for Polychlorinated Biphenyls in the UK Atmosphere (1991−2008)

Long-term air monitoring data sets are needed for persistent organic pollutants (POPs), to assess the effectiveness of source abatement measures and the factors controlling ambient levels. The Toxic Organic Micro-Pollutants (TOMPS) program in the United Kingdom started in 1991, generating a data set for polychlorinated biphenyls (PCBs). The history and volumes of production, usage, and subsequent restrictions on PCBs in the UK are well-characterized relative to many countries, providing a valuable case study on the effectiveness of controls and the factors influencing ambient levels and trends of these "model POPs". PCB air concentrations (congeners PCB 28, 52, 90/101, 118, 138, 153, and 180) from six rural and urban monitoring sites are presented. Most show a statistically significant decrease in PCBs levels over time, consistent with estimates of emissions, helping to validate emissions inventories. Times for a 50% decline in concentrations (sometimes called clearance rates) averaged 4.7 ± 1.6 years for all congeners at all sites. The trends at different sites and for different congeners were not statistically different from each other. Concentration differences between sites are correlated with local population density (i.e., the degree of urbanization), which supports approaches to modeling of primary emissions on the national and regional scale. The data set indicates that ambient levels and underlying trends of PCBs continue to reflect the controlling influence of diffuse primary sources from the ongoing stock of PCBs in urban environments. Production and use restrictions came into force in the UK over 40 years ago; trends since monitoring began in the early 1990s should be seen as part of a continuing decline in ambient levels since that time.

Continuous Monitoring of PCDD/Fs in the UK Atmosphere: 1991−2008

This study summarizes the key findings of a long-term (1991-2008) monitoring program to measure polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in urban and rural ambient air in the UK. Air concentrations are reported for 6 sites-3 urban (London, Manchester, and Middlesbrough) and 3 rural/semirural (Hazelrigg, High Muffles, and Stoke Ferry). Nearly 310 samples have been analyzed, each for a 3-month period. Annually averaged urban concentrations in the early 1990s were typically a few 100s fg (TEQ) m(-3) and <50 fg m(-3) in the mid-2000s. Applying first-order kinetics to the whole urban time series gave T1/2 (atmospheric half-lives) in London and Manchester of 3.2-5.9 and 4.1-5.9 years, respectively. Estimated national annual atmospheric emissions trends broadly correlated with the trends in urban ambient concentrations, suggesting that the inventory has captured the broad mixture of sources. However, rural air concentrations (in the low 10s fg m(-3)) show no discernible change since 1996, while recent urban concentrations are close to those in rural areas. Other UK trend data infer the declines in the 1990s followed previous declines in the 1980s from peak levels in the 1950-1970s, all before routine monitoring began. Winter concentrations are generally a factor of 2-3 higher than summer concentrations, implicating diffuse combustion sources (e.g., domestic space heating). These observations taken together suggest that most major readily controllable primary/point sources were reduced by the early/mid-1990s in the UK and that current ambient levels in both rural and urban areas may remain at broadly similar levels in the foreseeable future, unless there are major changes in energy requirements and generation options, fuel usage, and policy drivers.

A comparison of the isotopic composition of lead in rainwater, surface vegetation and tree bark at the long-term monitoring site, Glensaugh, Scotland, in 2007

The lead concentrations and isotopic ratios ( 206Pb/ 207Pb, 208Pb/ 206Pb, 208Pb/ 207Pb) of 31 rainwater (September 2006–December 2007) and 11 surface vegetation (moss, lichen, heather) samples (October 2007) from the rural upland catchment of Glensaugh in northeast Scotland and of nine bark samples (October 2007) from trees, predominantly Scots pine, in or near Glensaugh were determined. The mean 206Pb/ 207Pb ratios for rainwater in 2006 and 2007 were similar to those previously determined for 2000 to 2003 at Glensaugh, yielding an average mean annual value of 1.151 ± 0.005 (± 1 SD) for the period from 2000, when an outright ban on leaded petrol came into force in the UK, to 2007. The mean 206Pb/ 207Pb ratio (1.146 ± 0.004; n = 7) for surface vegetation near the top (430–450 m) of the catchment was not significantly different (Student's t test) from that of rainwater (1.148 ± 0.017; n = 24) collected over the 12-month period prior to vegetation sampling, but both were significantly different, at the 0.1% (i.e. p < 0.001) and 1% ( p < 0.01) level, respectively, from the corresponding mean value (1.134 ± 0.006; n = 9) for the outermost layer of tree bark. When considered in conjunction with similar direct evidence for 2002 and indirect evidence (e.g. grass, atmospheric particulates, dated peat) for recent decades in the Glensaugh area, these findings confirm that the lead isotopic composition of surface vegetation, including that of suitably located moss, reflects that of the atmosphere while that of the outermost layer of Scots pine bark is affected by non-contemporaneous lead. The nature and relative extent of the different contributory sources of lead to the current UK atmosphere in the era of unleaded petrol, however, are presently not well characterised on the basis of lead isotopic measurements.

Chemical speciation of PM2.5 particles at urban background and rural sites in the UK atmosphere

Fine particle (PM(2.5)) samples have been collected at two sites in the UK West Midlands, representing urban background (EROS) and rural (CPSS) locations. Chemical quantification has been carried out for major anions, metal species, total OC and EC, and for individual organic marker species including n-alkanes, hopanes, PAHs, organic acids and sterols. Concentration levels of each chemical group are presented and the patterns of individual species used to infer predominant sources of atmospheric fine particles from atmospheric measurements. Temporal and spatial variations are also discussed. The annual mean PM(2.5) concentrations were 11.6 and 10.5 microg m(-3), with large daily variations (2.7-37.1 microg m(-3)) at the two sites. Elevated PM(2.5) was mostly attributed to higher sulfate > OC > nitrate in summer and OC > nitrate > EC in winter. The mean levels of soil/dust related metals, Al > Si > Fe > Ca > Ti, were mostly different from other European sites due to differences in sampling site, local geology or climate, but comparable with earlier UK data. Trace metals, Zn > Cu > Pb > Mn > Ni, mostly showed lower concentrations compared with concentrations measured at the UK national metals network sites, except for Cu and Pb. The concentrations of PAHs were in a similar range to those previously measured within the UK, with an elevation at the urban site and in winter due to increased combustion activities, particularly for the two natural gas-related Oxy-PAHs. n-Alkanes showed a higher contribution in winter (low carbon preference index: 1.5-1.6) from anthropogenic emissions but in summer (high carbon preference index: 2.7-2.9) from biogenic sources, which are appreciable at our rural site (C(max) = 29). Similar levels of hopanes were observed at the urban (0.08-0.24 ng m(-3)) and the rural (0.07-0.23 ng m(-3)) site, with higher winter values at EROS as expected but opposite for CPSS. The concentrations of organic acids ranged from 0.19-10.2 ng m(-3) at EROS and 0.26-6.0 ng m(-3) at CPSS, with mixed patterns of seasonal variation (W/S: 0.54-2.0) for individual aliphatic and aromatic carboxylic acids, except the two resin acids which exhibited much higher levels in winter (W/S: 1.7-3.3) as expected due to higher wood smoke emissions. Cholesterol showed very low annual mean concentrations (0.13-0.16 ng m(-3)) confirming that meat cooking is not an important source at our sites.

Source apportionment of fine particles at urban background and rural sites in the UK atmosphere

Airborne fine particulate matter (PM 2.5) has been collected at two sites in the West Midlands conurbation, UK, representing urban background and rural locations. Chemical analyses have been carried out for major anions, trace metals, total OC and EC, and for individual organic marker species including n-alkanes, hopanes, PAHs, organic acids and sterols. Source apportionment has been conducted using both a pragmatic mass closure model and the US EPA chemical mass balance (CMB) model. The pragmatic mass closure model is well able to account for the measured PM 2.5 mass in terms of chemical/source components, and the chemical mass balance model has been used to apportion the carbonaceous component of the aerosol. The dominant components of PM 2.5 at both sites are secondary inorganic (sulphate and nitrate) and carbonaceous particles. The CMB model shows the latter to arise mainly from road traffic sources, with smaller contributions from vegetative detritus, wood smoke, natural gas, coal, and dust/soil. The CMB model also identifies an important component of the organic aerosol not associated with these primary sources, which correlates very strongly with secondary organic aerosol estimated from the OC/EC ratio. The split between different automotive source types does not relate well to UK emission inventories, and may indicate that CMB source profiles from North American studies and different carbon analysis protocols may lead to erroneous conclusions.

PCDD/F and “Dioxin-like” PCB emissions from iron ore sintering plants in the UK

Investigations have been carried out at the three Corus UK sinter plants over the period 2002–2004 to characterise the emissions of both 2,3,7,8-PCDD/Fs and WHO-12 PCBs, to estimate annual mass releases of these organic micro-pollutants using the I-TEF and WHO-TEF schemes, and to investigate the formation of PCBs in the iron ore sintering process. Results showed that the sintering of iron ore produces a characteristic WHO-12 PCB and PCDD/F congener pattern that is substantially the same for all UK sinter plants. With regard to WHO-12 PCBs, the most abundant congeners were typically PCBs 118 (6–9 ng N m −3), 105 (2–4 ng N m −3) and 77 (2–3 ng N m −3). All other WHO-12 PCBs were also detected at concentrations around 1 ng N m −3. All sinter plants investigated exhibited very similar TEQ concentrations. WHO-12 PCB emissions were in the range 0.042–0.111 ng WHO-TEQ N m −3, whereas PCDD/F emissions ranged from 0.39 to 1.62 ng WHO-TEQ N m −3. PCDF congeners were the main contributors to the overall TEQ in sintering emissions (ca. 85%). Amongst WHO-12 PCBs, PCB 126 was the only noteworthy contributor to total TEQ (ca. 5–7%), a similar contribution to that from PCDDs. Based on the measurements that Corus UK has undertaken at these three sinter plants, annual mass releases of WHO-12 PCBs and PCDD/Fs have been calculated. For UK sinter plants, a total mass release of 29.5 g WHO-TEQ per annum [WHO-12 PCBs + PCDD/Fs] has been estimated, representing 9% of the total PCDD/F emissions to the UK atmosphere. Measurements were also carried out at a UK sinter plant to determine the windleg emission profile of WHO-12 PCBs. Results showed that WHO-12 PCBs were formed in the same regions of the sinter strand as 2,3,7,8-PCDD/Fs, indicating that there was a strong correlation between the formation of WHO-12 PCBs and PCDD/Fs in the iron ore sintering process.

A congener-specific PCDD/F emissions inventory for the UK: do current estimates account for the measured atmospheric burden?

Considerable effort has been expended in the UK and elsewhere to quantify and rank PCDD/F primary sources and emissions to the environment, principally the atmosphere, so that cost-effective source reduction measures can be taken. Here, we predict a congener-specific emissions inventory for primary and secondary nondioxin-regulated sources to the UK atmosphere, estimated to have ranged from 3 to 22 kg in 1996. The inventory profile is dominated by OCDD (∼30–40%), 1,2,3,4,6,7,8-HpCDD (∼15–19%) and 1,2,3,4,6,7,8-HpCDF (∼14–19%). Congeners 2,3,4,7,8-PeCDF and 1,2,3,7,8-PeCDD dominate the ΣTEQ composition. Mass balance modelling suggests that the predicted congener pattern in UK air (based on the emission inventory) is similar to observed measurements, with absolute concentrations being estimated within a factor of 2 for most congeners. Calculations taking into account atmospheric weathering processes and long range (advective) transport suggest that PCDD/F sources to ambient air are primarily ongoing and that atmospheric mixing will mask individual emission source profiles/identities. This supports measured evidence for the consistency of PCDD/F air profiles observed around the UK throughout the year.

Occurrence of C 10–C 13 polychlorinated n-alkanes in the atmosphere of the United Kingdom

Short-chain (C 10–C 13) polychlorinated n-alkanes (PCAs) have been measured in the air in the United Kingdom at 2 week intervals over a period of 12 months. The mean concentration of PCAs over the sampling period was 320±320 pg m −3 (arithmetic mean±1 S.D.) with a geometric mean of 160 pg m −3. Hexa- and hepta-chlorinated dodecane congeners are the predominant PCA components in the UK atmosphere. Analyses of gas phase and particulate phase PCAs indicate that 95% of the PCA content of the atmosphere is in the gas phase. No seasonal trend or dependence on temperature was observed. The data can be divided into 2 significantly different ( P<0.01) populations: one group of incidences of lower concentrations of 150±110 pg m −3 and one of higher concentrations of 800±170 pg m −3. The incidences of elevated concentrations could not be related to increased air temperature or other meteorological factors on the time-scale employed and suggest that atmospheric PCA concentrations in the UK may be dominated by episodic incidences of advective transport of contaminated air masses and/or releases to the environment from regional primary point sources rather than by temperature-dependent transport processes. Levels of PCAs in the UK atmosphere are similar to values obtained at a semi-rural location in Canada and at least an order of magnitude higher than in the Canadian Arctic atmosphere. These data represent the first detailed study on the occurrence of PCAs in the atmosphere and show that PCAs can be a major component of the persistent organic pollutant burden of the atmosphere which has the potential of undergoing long-range atmospheric transport processes.

Major component contributions to PM 10 composition in the UK atmosphere

Physical and chemical characteristics of PM 10, including chloride, nitrate, sulphate, and black smoke, have been measured on a seasonal basis at four coastal, rural, and urban sites across the UK. Weekly campaigns with 6 h sample resolution were conducted, and the results related to meteorological conditions and air mass back trajectories. Seasonal and location- specific mean values are reported, along with an indication of diurnal characteristics. Although the urban site reflected generally higher values for the anthropogenic pollutants, long-range transport of primary and secondary particles was significant. The data have been analysed using a four-component multi-linear regression model including black smoke as a surrogate for primary combustion particles, secondary particles (sulphate and nitrate), chloride, and a constant which describes “other”, mainly coarse mode particles. Regression coefficients have been calculated on a site and seasonal basis. “Other” particles were higher during the summer and in the urban environment with an overall mean value of 5 μg m −3. Secondary nitrate and sulphate were strongly related to meteorological conditions and less to location. Overall, the four-component model accounts quite well ( r 2=0.76 for all data) for PM 10 mass and for some sites and seasons gives an excellent fit to the data. Addition of dummy variables representing season, urban/rural location and time of sampling gives an improvement in fit, with r 2=0.84 . Application of the coefficients derived from the “all data” model shows secondary particles contributing 28–35% of site-mean PM 10, primary combustion particles from 20 to 57%, sodium chloride, 11–34% and “other”, mainly crustal particles, 3–21%. It is felt that this probably underestimates the crustal contribution, but the reasons are unclear.

Measuring and modelling the vertical distribution of semi-volatile organic compounds in soils. II: model development

A dynamic air-soil exchange model which divides the soil into multiple soil layers has been developed and used to simulate the vertical distribution of PCBs in an undisturbed grassland soil. An historical emission profile for PCBs to the UK atmosphere was used to deduce concentrations in the air compartment. Model simulations were tuned by varying the most uncertain model input parameters, namely soil turnover rates by bioturbation and emission estimates. Comparison of model output and reported PCB concentration profiles agreed within a factor of six. Insights were gained into the relative importance of the soil transport processes and specifically bioturbation was shown to be the dominant transport mechanism for PCBs in this soil. It was concluded that the model is sufficiently accurate for incorporation into regional mass balance models, although vertical layering of the soil may be unnecessary in models describing the long-term air-soil interaction of organic compounds.

Temperature dependence of PCBs in the UK atmosphere

A thermodynamic approach was taken to assess the state of equilibrium between air and the Earth’s surface for PCBs at a variety of sites located in urban and rural areas. The Clausius–Clapeyron equation was applied to atmospheric PCB data, relating PCB partial vapour pressure (ln P) to inverse temperature (1/K); essentially representing the temperature controlled transition between condensed phases and the atmospheric gas phase. The slopes of the resulting plots ranged from −3100 to −8272 for a range of congeners at two city sites, significantly steeper than those generated at two rural locations, where there was little or no correlation between ln P and temperature. It was inferred that advection and variable meteorological conditions mask any localised, temperature dependent, air–surface exchange at these rural locations when weekly or two weekly integrated samples were taken. At a third rural site, close to Lancaster University, an intensive highly time-resolved sampling regime, carried out during very stable meteorological conditions resulted in highly correlated plots ( r 2>0.6), with slopes ranging from −7151 to −14 148 for different congeners. By reducing meteorological variables in this manner localised temperature controlled air–surface exchange became evident. Enthalpies of phase change generated from the temperature coefficients were similar to literature values for the enthalpy of vapourisation and the enthalpy of phase change from octanol to air. This suggests that, under these stable conditions, equilibrium was achieved as a function of either vapour pressure ( P ° L) or the octanol–air partition coefficient ( K OA).

A study of the spatial distribution of PCBs in the UK atmosphere using pine needles

Past and current polychlorinated biphenyl (PCB) inputs to the environment, mainly in industrialized countries, continue to determine a global re-distribution of these contaminants. In order to better understand PCB transport and distribution phenomena, a number of large-scale distribution studies have been recently published in the literature. In this paper a nationwide survey of 28 pine needle samples taken across the UK is presented. Mean PCB concentrations of a number of latitudinal bands (transects) revealed the presence of a decreasing concentration gradient from southern England to northern Scotland of a factor of ∼7. The pine needle data also provide evidence to suggest: 1) that there has been a decrease in the PCB concentration of the atmosphere in the southern UK; and 2) there is a relationship between regional mean needle PCB concentrations and population densities. Calculated air concentrations from the pine needle results were compared with measured literature data of a similar area to test the possibility of using bioconcentration factors (BCF) based on n-octanol: air partition coefficients (Koa) to predict air-leaf equilibrium of semivolatile organic compounds. A more detailed analysis, in accordance with some literature data, has revealed that uncertainties arise when leaf-air uptake of molecules with high Koa values (Log Koa > 8–9) is modelled.

An updated inventory of potential PCDD and PCDF emission sources in the UK

This study updates previous estimates of emissions to the UK atmosphere of polychlorinated dibenzo- p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Following a systematic screening of a range of industrial processes operating in the UK for the potential to release PCDD Fs to atmosphere, 23 industrial processes were shortlisted for further consideration as potential emitters. To these processes were added six non-industrial sources of PCDD F emissions; domestic coal and wood combustion, crematoria, traffic, natural fires and accidental fires. For each shortlisted process emission factors were identified. Emission factors were combined with the quantity of material treated or produced to generate an estimate of the annual quantity of PCDD Fs released to atmosphere. The total estimated current emissions to atmosphere ranged from 560 to 1100 g I-TEQ year −1, with industrial processes contributing 535–955 g I-TEQ year −1, an average of approximately 90% of the total inventory. Emissions from MSW incineration plants were dominant, contributing an average of 70% to the total emissions from industrial sources. Emissions from coal combustion, sinter plants, iron and steel plants, non-ferrous metals operations and incineration of clinical waste collectively contributed an average of 25% to total industrial emissions in roughly equal proportions. The effect of tightening emission controls was also examined. Assuming a situation when current regulations concerning PCDD F emissions are fully implemented, a reduction in emissions from 560–1100 g I-TEQ year −1 to 110–350 g I-TEQ year −1 is envisaged. The largest reduction is effected through the imposition of a 1 ng I-TEQ m −3 emission limit on MSW and clinical waste incinerators: the contribution from these sources falls from the present range of 60–85% to approximately 6–18% of total emissions.

The chemical composition of airborne particles in the UK atmosphere

Published data collected over the past fifteen years relating to the elemental and ionic composition and chemical speciation of both inorganic and organic components of airborne particles collected at (predominantly urban) United Kingdom sites have been reviewed. Whilst there have been no studies of total composition and few consistent studies of major components, there are high quality long-term survey data on trace metals and some specific organic compounds. The available data are described and, where possible, a view on “typical” composition presented.

Polynuclear aromatic hydrocarbons in the United Kingdom environment: A preliminary source inventory and budget

This paper presents the first attempt to quantify the production, cycling, storage and loss of PAHs in the UK environment. Over 53 000 tonnes of ∑PAHs (sum of 12 individual compounds) are estimated to reside in the contemporary UK environment, with soil being the major repository. If soils at contaminated sites are included, this estimate increases dramatically. Emission of PAHs to the UK atmosphere from primary combustion sources are estimated to be greater than 1000 tonnes ∑PAHs per annum, with over 95% coming from domestic coal combustion, unregulated fires and vehicle emissions. It is estimated that approximately 210 tonnes of ∑PAH are delivered to terrestrial surfaces each year via atmospheric deposition. Therefore, inputs of PAHs to the UK atmosphere outweigh the outputs by a factor of over 4. This may be explained by enhanced particulate deposition near point sources, PAH degradation in the atmosphere and transport away from the UK with prevailing winds. Disposal of waste residues is estimated to contribute a further 1000 tonnes of ∑PAH per year to the terrestrial environment. It is illustrated that the use of creosote has the potential to release considerable quantities of PAHs to the UK environment. Temporal trends in PAH cycling are then considered. There is good evidence to suggest that air concentrations and fluxes to the UK surface are now lower than at any time throughout this century. Nonetheless, the UK ∑PAH burden is still increasing at the present time, principally through retention by soils. However, there are marked differences in the behaviour of individual compounds: there is evidence, for example, that phenanthrene concentrations in soils have declined since the 1960s, although soil concentrations of benzo[a]pyrene and other heavier PAHs have continued to increase through this century. Volatilisation of low molecular weight PAHs accumulated in soils over previous decades may be making an important contribution to the current atmospheric burden. The major uncertainties identified by data on this budget are: (1) the lack of PAH concentrations in some environmental matrices; (2) the possible importance of contaminated soils as a major repository and source of PAHs; (3) the lack of emission data (especially vapour phase releases) for some PAH sources; (4) the importance of biodegradation and volatilisation as loss mechanisms for low molecular weight PAHs in soils; and (5) the importance of creosote use in the PAH cycle.