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    ABSTRACT: This paper develops the idea of bivariate polar plots as a method for source detection and characterisation. Bivariate polar plots provide a graphical method for showing the joint wind speed, wind direction dependence of air pollutant concentrations. Bivariate polar plots provide an effective graphical means of discriminating different source types and characteristics. In the current work we apply k-means clustering techniques directly to bivariate polar plots to identify and group similar features. The technique is analogous to clustering applied to back trajectories at the regional scale. When applied to data from a monitoring site with high source complexity it is shown that the technique is able to identify important clusters in ambient monitoring data that additional analysis shows to exhibit different source characteristics. Importantly, this paper links identified clusters to known emission characteristics to confirm the inferences made in the analysis. The approaches developed should have wide application to the analysis of air pollution monitoring data and have been made freely available as part of the openair R package.
    Environmental Modelling and Software 01/2013; 40:325 - 329.
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    ABSTRACT: In this paper we have compared detailed road traffic NOx emissions with the equivalent trends in ambient roadside NOx measurements. This was undertaken separately in Great Britain and London, for all of the major roads, and by road type and location. The emissions trends were created using different emissions factors, those used in UK emissions inventories (Base case), the Swiss-German handbook (HBEFA), and those created from recent remote sensing measurements in the UK (RSD). An alternative assumption for use of Selective Catalytic Reduction (SCR) in the articulated Heavy Goods Vehicle (HGV) fleet was also tested. For all scenarios traffic flows, speeds and vehicle age were kept constant. Comparison between the emissions scenarios in Great Britain showed that by 2009, NOx emissions estimates from road traffic could be as much as 25% greater than current UK estimates and 31% greater in London. The RSD emissions inventory gave the smallest downward trend in NOx emissions, from 2004 to 2009, of between 3 and 4%/year and this compared with a reduction of ∼6%/year from the Base Case and HBEFA scenarios. All scenarios compared poorly with roadside NOx measurement trends from UK sites, which typically reduce by between 1% and 2%/year. We have shown that the differences in NOx emissions trends were driven, partially at least, by the relative contribution from light duty diesel vehicles. An analysis from 2700 NOx measurement sites throughout Europe has shown that this problem is unlikely to be limited to the UK, and identifies a difficulty in meeting EU limit values for NO2, obligations under the National Emission Ceilings Directive (NECD, 2001) and the Gothenburg Protocol (UNECE, 1999) and for forecasting future changes in PM2.5.
    Atmospheric Environment 07/2012; 54:107–116.
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    ABSTRACT: The eruption of the Icelandic volcano Eyjafjallajökull in April 2010 resulted in an unprecedented flight-ban at many European airports for many days. While much of the scientific interest in the eruption was related to the chemical and physical properties of the ash cloud and how it dispersed, a secondary effect was the reduction in aviation emissions at airports around Europe and elsewhere. In this study we aim to quantify the impact the flight-ban had on concentrations of nitrogen oxides at measurement sites close to London Heathrow Airport. A technique based on boosted regression trees is used to build an explanatory model of NOx and NO2 concentrations based on hourly meteorological and aircraft emissions data in the 3-years preceding the flight-ban. We show that the airport closure resulted in an unambiguous effect on NOx and NO2 concentrations close to the airport, even though the ban only lasted six days. Furthermore, we estimate the annual impact airport emissions have on mean concentrations of NOx and NO2 for different years and compare these estimates with a detailed dispersion modelling study and previous work that was based on the analysis of monitoring site data. For the receptor most affected by the flight-ban approximately 200 m south of the airport we estimate the airport contributes about 13.5 μg m−3 NOx (≈23% of the total measured NOx concentration), which is similar in magnitude to detailed dispersion modelling estimates of 12.0 μg m−3, but approximately twice that of other estimates based on the analysis of ambient measurements. Other measurement sites showed more mixed results due to the prevailing meteorology at the time of the ban, which affected the extent to which these sites were affected by the flight-ban. The techniques developed and applied in this paper would have application to other short-term interventions that affect air quality.
    Atmospheric Environment 01/2012; 54:328-336.
  • Atmospheric Environment 07/2011; 45(23):3911-3912.
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    ABSTRACT: Adverse cardiorespiratory health is associated with exposure to ambient particulate matter (PM). The highest PM concentrations in London occur in proximity to waste transfer stations (WTS), sites that experience high numbers of dust-laden, heavy-duty diesel vehicles transporting industrial and household waste. Our goal was to quantify the contribution of WTS emissions to ambient PM mass concentrations and oxidative potential. PM with a diameter < 10 microm (PM10) samples were collected daily close to a WTS. PM10 mass concentrations measurements were source apportioned to estimate local versus background sources. PM oxidative potential was assessed using the extent of antioxidant depletion from a respiratory tract lining fluid model. Total trace metal and bioavailable iron concentrations were measured to determine their contribution to PM oxidative potential. Elevated diurnal PM10 mass concentrations were observed on all days with WTS activity (Monday-Saturday). Variable PM oxidative potential, bioavailable iron, and total metal concentrations were observed on these days. The contribution of WTS emissions to PM at the sampling site, as predicted by microscale wind direction measurements, was correlated with ascorbate (r = 0.80; p = 0.030) and glutathione depletion (r = 0.76; p = 0.046). Increased PM oxidative potential was associated with aluminum, lead, and iron content. PM arising from WTS activity has elevated trace metal concentrations and, as a consequence, increased oxidative potential. PM released by WTS activity should be considered a potential health risk to the nearby residential community.
    Environmental Health Perspectives 04/2010; 118(4):493-8.
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    ABSTRACT: London currently has the highest nitrogen dioxide (NO2) concentration recorded for any European city and for particulate matter (PM) it has some of the worst hot spots. Therefore overall, for these two pollutants, London is the worst in the UK and amongst the worst in Europe. Exposure to elevated concentrations of air pollutants such as PM and NO2 has well-established heath effects and most countries now have strict guidelines for air quality. London's air quality problems are driven largely by traffic. This, along with the high density of people in an urban area results in air quality guidelines being exceeded on a regular basis and large numbers of people being affected. In an attempt to combat London's air quality problems the Mayor of London introduced a series of measures to decrease traffic emissions. These included both a restriction on the number of vehicles entering central London each day--the Congestions Charging Scheme (CCS), and the discouragement of the most polluting heavy goods vehicles from entering--the London Low Emission Zone (LEZ). Together, it is hoped that these measures will lead to an improvement in air quality and provide a direct health benefit to Londoners. Research underway is charting the progress of this real world experiment.
    Biomarkers 07/2009; 14 Suppl 1:5-11.
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    ABSTRACT: We modelled exposure to traffic particles using a latent variable approach and investigated whether long-term exposure to traffic particles is associated with an increase in the occurrence of acute myocardial infarction (AMI) using data from a population-based coronary disease registry. Cases of individually validated AMI were identified between 1995 and 2003 as part of the Worcester Heart Attack Study. Population controls were selected from Massachusetts, USA, resident lists. NO(2) and PM(2.5) filter absorbance were measured at 36 locations throughout the study area. The air pollution data were used to estimate exposure to traffic particles using a semiparametric latent variable regression model. Conditional logistic models were used to estimate the association between exposure to traffic particles and occurrence of AMI. Modelled exposure to traffic particles was highest near the city of Worcester. Cases of AMI were more exposed to traffic and traffic particles compared to controls. An interquartile range increase in modelled traffic particles was associated with a 10% (95% CI 4% to 16%) increase in the odds of AMI. Accounting for spatial dependence at the census tract, but not block group, scale substantially attenuated this association. These results provide some support for an association between long-term exposure to traffic particles and risk of AMI. The results were sensitive to the scale selected for the analysis of spatial dependence, an issue that requires further investigation. The latent variable model captured variation in exposure, although on a relatively large spatial scale.
    Occupational and environmental medicine 07/2009; 66(12):797-804.
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    ABSTRACT: EU Directives stipulate that PM10 should be measured using the gravimetric reference method as laid out in EN12341 [CEN, 1998. Air Quality – Determination of the PM10 Fraction of Suspended Particulate Matter – Reference Method and Field Test Procedure to Demonstrate Reference Equivalence of Measurement Methods. European Committee for Standardisation], or an equivalent method as demonstrated using EC guidance [EC, 2005. Demonstration of Equivalence of Ambient Air Monitoring Methods. European Commission Working Group on Guidance for the Demonstration of Equivalence]. There is however a conflict between the requirement to measure PM10 using the gravimetric reference method and the need for rapid public reporting, and many member states, including the UK, rely on non-gravimetric techniques to measure PM10. In the UK the majority of PM10 measurements are made using the Tapered Element Oscillating Microbalance (TEOM), which does not meet the equivalence criteria [Harrison, D., 2006. UK Equivalence Programme for Monitoring of Particulate Matter. Defra, London]. The implied need to upgrade or replace TEOMs with an equivalent automated measurement technique has significant cost implications. The model described in this paper was based on analysis of daily mean measurements of PM10 by the Filter Dynamics Measurement System (FDMS) and the TEOM at UK sites. It uses the FDMS measurement of the volatile component of PM10 (referred to here as FDMS purge) to correct for differences in the sensitivity to volatile PM10 between the TEOM and the EU gravimetric reference method. The model equation for the correction of TEOM PM10 measurements is: TEOMVCM = TEOM − 1.87 FDMS purge due to the regional homogeneity of volatile PM, the FDMS purge concentration may be measured at a site distant to the TEOM, allowing the possibility of using a single FDMS instrument to correct PM10 measurements made by several TEOMs in a defined geographical area. The model was assessed against the criteria for the EC Working Group's Guidance for the Demonstration of Equivalence of Ambient Air Monitoring Methods [EC, 2005. Demonstration of Equivalence of Ambient Air Monitoring Methods. European Commission Working Group on Guidance for the Demonstration of Equivalence]. The model satisfies the equivalence criteria using remote FDMS purge measurements for distances up to 200 km (in 22 out of 23 data sets). These data provide strong evidence that the model is a viable tool for correcting measurements from TEOM instruments on the national and local government networks.
    Atmospheric Environment - ATMOS ENVIRON. 01/2009; 43(13):2132-2141.
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    ABSTRACT: To alleviate traffic congestion in Central London, the Mayor introduced the Congestion Charging Scheme (CCS) in February 2003. We modelled the impact of the CCS on levels of traffic pollutants, life expectancy and socioeconomic inequalities. Annual average NO(2) and PM(10) were modelled using an emission-dispersion model. We assumed the meteorology and vehicle fleet remained constant during the pre- and post-CCS periods to isolate changes due to traffic flow. Air pollution concentrations were linked to small area socioeconomic, population and mortality data. Associated changes in life expectancy were predicted using life table analysis and exposure-response coefficients from the literature. Before the introduction of the CCS, annual average NO(2) was 39.9 microg/m(3) and PM(10) was 26.2 microg/m(3) across Greater London. Concentrations were 54.7 microg/m(3) for NO(2) and 30.3 microg/m(3) for PM(10) among census wards within or adjacent to the charging zone. Absolute and relative reductions in concentrations following the introduction of the CCS were greater among charging zone wards compared to remaining wards. Predicted benefits in the charging zone wards were 183 years of life per 100,000 population compared to 18 years among the remaining wards. In London overall, 1888 years of life were gained. More deprived areas had higher air pollution concentrations; these areas also experienced greater air pollution reductions and mortality benefits compared to the least deprived areas. The CCS, a localised scheme targeting traffic congestion, appears to have modest benefit on air pollution levels and associated life expectancy. Greater reductions in air pollution in more deprived areas are likely to make a small contribution to reducing socioeconomic inequalities in air pollution impacts.
    Occupational and environmental medicine 03/2008; 65(9):620-7.
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    ABSTRACT: The clinical severity of sickle-cell disease (SCD) is dependent on genetic and environmental variables. Environmental factors have been poorly studied. We have investigated possible links between air pollution and acute pain in SCD. We retrospectively studied the numbers of daily admissions with acute sickle-cell pain to King's College Hospital, London, in relation to local daily air quality measurements. We analysed 1047 admissions over 1400 d (1st January 1998-31st October 2001). Time series analysis was performed using the cross-correlation function (CCF). CCF showed a significant association between increased numbers of admissions and low levels of nitric oxide (NO), low levels of carbon monoxide (CO) and high levels of ozone (O(3)). There was no association with sulphur dioxide (SO(2)), nitrogen dioxide or PM(10) (dust). The significant results were further examined using quartile analysis. This confirmed that high levels of O(3) and low levels of CO were associated with increased numbers of hospital admissions. Low NO levels were also associated with increased admissions but did not reach statistical significance on quartile analysis. Our study suggests air quality has a significant effect on acute pain in SCD and that patients should be counselled accordingly. The potential beneficial effect of CO and NO is intriguing and requires further investigation.
    British Journal of Haematology 04/2007; 136(6):844-8.
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