Imperial College London

DrDavidGreen

Faculty of MedicineSchool of Public Health

Senior Research Fellow
 
 
 
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d.green

 
 
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Norfolk PlaceSt Mary's Campus

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Summary

 

Publications

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76 results found

Delgado-Saborit JM, Lim S, Hickman A, Baker C, Barratt B, Cai X, Font A, Heal MR, Lin C, Thornes JE, Woods M, Green Det al., 2022, Factors affecting occupational black carbon exposure in enclosed railway stations, Atmospheric Environment, Vol: 289, Pages: 1-14, ISSN: 1352-2310

Many rail services around the world continue to use diesel as the primary fuel source and enclosed railway stations have been identified as a possible hotspot for exposure to harmful diesel exhaust exposures. Little is known about the occupational exposure to air pollution for railway station workers due to their mobility around the station and variations in station design. A detailed understanding of the concentration of black carbon (BC), a diesel exhaust tracer, inside railway stations and the factors driving occupational exposures is required to minimize occupational exposure. Real-time personal exposure to BC was measured during 60 work-shifts encompassing different roles at three large enclosed railway stations of different design in London, Birmingham and Edinburgh (UK). Sampling was conducted by the train station workers over a period of 27 days between January 2017 to October 2018. Worker shift-mean BC exposures ranged 0.6–20.8 μg m−3 but 1-min peak exposures reached 773 μg m−3, with train dispatchers experiencing the highest BC exposures. Station design, job role, and frequency of diesel trains were the main drivers of occupational BC exposure. Elevated exposures for some station workers indicate that mitigation measures to reduce their exposure should be implemented to lower the risk of occupational health impacts. These could include improving ventilation and reducing engine emissions.

Journal article

Muxworthy A, Lam C, Green D, Cowan A, Maher B, Gonet Tet al., 2022, Magnetic characterisation of London’s airborne nanoparticulate matter, Atmospheric Environment, Vol: 287, Pages: 1-8, ISSN: 1352-2310

Iron-bearing particulate matter produced by vehicle emissions is known to be toxic. To better quantify potential health risks, we have conducted the first magnetic study of a time-series of London's inhalable particulate matter (<10 μm, PM10), captured by three monitoring stations in central London (Marylebone Road, Earl's Court Road and Oxford Street) through 2010 and 2012. We conducted room-temperature analysis on all the samples, and a limited number of samples were analysed at both high and low temperatures. The high-temperature measurements identified magnetite as the dominant magnetic phase. The low-temperature measurements revealed high numbers of nanoparticles, which, assuming magnetite, are in the grain-size range 1–4 nm. It is estimated that as much as ∼40% of the total magnetic signal at 10 K is from particles <4 nm, that are magnetically ‘invisible’ at room-temperature and are being routinely under-estimated in room temperature-based magnetic studies. From the low-temperature measurements, the total concentration of magnetite was estimated at ∼7.5%, significantly higher than previously reported. The room-temperature magnetic data were compared with other pollution data, e.g., NOX and PM10, and meteorological data. Mass-dependent terms like the saturation magnetisation were found to display a strong correlation with NOX and PM10, indicating a common source for these pollutants, i.e., vehicle emissions. Magnetic coercivity measurements, which are independent of abundance, and provide information on grain-size, were consistent across all three sampling localities, again suggesting a major dominant source. Relatively small variations in coercivity were correlated with meteorological events, e.g., temperature and precipitation, suggesting preferential removal of larger airborne grains, i.e., >50 nm.

Journal article

Chen G, Canonaco F, Tobler A, Aas W, Alastuey A, Allan J, Atabakhsh S, Aurela M, Baltensperger U, Bougiatioti A, De Brito JF, Ceburnis D, Chazeau B, Chebaicheb H, Daellenbach KR, Ehn M, El Haddad I, Eleftheriadis K, Favez O, Flentje H, Font A, Fossum K, Freney E, Gini M, Green DC, Heikkinen L, Herrmann H, Kalogridis A-C, Keernik H, Lhotka R, Lin C, Lunder C, Maasikmets M, Manousakas MI, Marchand N, Marin C, Marmureanu L, Mihalopoulos N, Močnik G, Nęcki J, O'Dowd C, Ovadnevaite J, Peter T, Petit J-E, Pikridas M, Matthew Platt S, Pokorná P, Poulain L, Priestman M, Riffault V, Rinaldi M, Różański K, Schwarz J, Sciare J, Simon L, Skiba A, Slowik JG, Sosedova Y, Stavroulas I, Styszko K, Teinemaa E, Timonen H, Tremper A, Vasilescu J, Via M, Vodička P, Wiedensohler A, Zografou O, Cruz Minguillón M, Prévôt ASHet al., 2022, European aerosol phenomenology - 8: Harmonised source apportionment of organic aerosol using 22 Year-long ACSM/AMS datasets, Environment International, Vol: 166, ISSN: 0160-4120

Organic aerosol (OA) is a key component of total submicron particulate matter (PM1), and comprehensive knowledge of OA sources across Europe is crucial to mitigate PM1 levels. Europe has a well-established air quality research infrastructure from which yearlong datasets using 21 aerosol chemical speciation monitors (ACSMs) and 1 aerosol mass spectrometer (AMS) were gathered during 2013-2019. It includes 9 non-urban and 13 urban sites. This study developed a state-of-the-art source apportionment protocol to analyse long-term OA mass spectrum data by applying the most advanced source apportionment strategies (i.e., rolling PMF, ME-2, and bootstrap). This harmonised protocol was followed strictly for all 22 datasets, making the source apportionment results more comparable. In addition, it enables quantification of the most common OA components such as hydrocarbon-like OA (HOA), biomass burning OA (BBOA), cooking-like OA (COA), more oxidised-oxygenated OA (MO-OOA), and less oxidised-oxygenated OA (LO-OOA). Other components such as coal combustion OA (CCOA), solid fuel OA (SFOA: mainly mixture of coal and peat combustion), cigarette smoke OA (CSOA), sea salt (mostly inorganic but part of the OA mass spectrum), coffee OA, and ship industry OA could also be separated at a few specific sites. Oxygenated OA (OOA) components make up most of the submicron OA mass (average = 71.1%, range from 43.7 to 100%). Solid fuel combustion-related OA components (i.e., BBOA, CCOA, and SFOA) are still considerable with in total 16.0% yearly contribution to the OA, yet mainly during winter months (21.4%). Overall, this comprehensive protocol works effectively across all sites governed by different sources and generates robust and consistent source apportionment results. Our work presents a comprehensive overview of OA sources in Europe with a unique combination of high time resolution (30-240 min) and long-term data coverage (9-36 months), providing essential information

Journal article

Fussell JC, Franklin M, Green DC, Gustafsson M, Harrison RM, Hicks W, Kelly FJ, Kishta F, Miller MR, Mudway IS, Oroumiyeh F, Selley L, Wang M, Zhu Yet al., 2022, A Review of road traffic-derived non-exhaust particles: emissions, physicochemical characteristics, health risks, and mitigation measures., Environmental Science and Technology (Washington), Vol: 56, ISSN: 0013-936X

Implementation of regulatory standards has reduced exhaust emissions of particulate matter from road traffic substantially in the developed world. However, nonexhaust particle emissions arising from the wear of brakes, tires, and the road surface, together with the resuspension of road dust, are unregulated and exceed exhaust emissions in many jurisdictions. While knowledge of the sources of nonexhaust particles is fairly good, source-specific measurements of airborne concentrations are few, and studies of the toxicology and epidemiology do not give a clear picture of the health risk posed. This paper reviews the current state of knowledge, with a strong focus on health-related research, highlighting areas where further research is an essential prerequisite for developing focused policy responses to nonexhaust particles.

Journal article

Stettler MEJ, Nishida RT, de Oliveira PM, Mesquita LCC, Johnson TJ, Galea ER, Grandison A, Ewer J, Carruthers D, Sykes D, Kumar P, Avital E, Obeysekara AIB, Doorly D, Hardalupas Y, Green DC, Coldrick S, Parker S, Boies AMet al., 2022, Source terms for benchmarking models of SARS-CoV-2 transmission via aerosols and droplets., R Soc Open Sci, Vol: 9, ISSN: 2054-5703

There is ongoing and rapid advancement in approaches to modelling the fate of exhaled particles in different environments relevant to disease transmission. It is important that models are verified by comparison with each other using a common set of input parameters to ensure that model differences can be interpreted in terms of model physics rather than unspecified differences in model input parameters. In this paper, we define parameters necessary for such benchmarking of models of airborne particles exhaled by humans and transported in the environment during breathing and speaking.

Journal article

Manousakas M, Furger M, Daellenbach KR, Canonaco F, Chen G, Tobler A, Rai P, Qi L, Tremper AH, Green D, Hueglin C, Slowik JG, El Haddad I, Prevot ASHet al., 2022, Source identification of the elemental fraction of particulate matter using size segregated, highly time-resolved data and an optimized source apportionment approach, Atmospheric Environment: X, Vol: 14, ISSN: 2590-1621

Source emissions with high covariance degrade the performance of multivariate models, and often highly-time resolved data is needed to accurately extract the contribution of different emissions. Here, we use highly time-resolved size segregated elemental composition data to apportion the sources of the elemental fraction of PM in Zürich (May 2019–May 2020). For data collection, we have used an ambient metals monitor, Xact 625i, equipped with a sampling inlet alternating between PM2.5 and PM10. By implementing interpolation and a newly proposed uncertainty estimation methodology, it was possible to obtain and use in PMF a combined dataset of PM2.5 and PMcoarse (PM10-2.5) having data from only one instrument. The combination of the inlet switching system, the instrument's high time resolution, and the use of advanced source apportionment approaches yielded improved source apportionment results in terms of the number of identified sources, as the model, additionally to the diurnal and seasonal variation of the dataset, also utilizes the variation from the size segregated data. Thirteen sources of elements were identified, i.e., sea salt (5.4%), biomass burning (7.2%), construction (4.3%), industrial (3.3%), light-duty vehicles (5.4%), Pb (0.7%), Zn (0.7%), dust (22.1%), transported dust (9.5%), sulfates (15.4%), heavy-duty vehicles (17%), railway (6.6%) and fireworks (2.4%). The Covid-19 lockdown effect in PM sources in the area was also quantified. High-intensity events disproportionally affect the PMF solution, and in many cases, they are getting discarded before analysis, removing thus valuable information from the dataset. In this study, a three-step source apportionment approach was used to get a well-resolved unmixed solution when firework data points were included in the analysis. This approach can also be used for other sources and/or events with very high contributions that distort source apportionment analysis. Optimized source apportionment techni

Journal article

Tremper A, Jephcote C, Gulliver J, Hibbs L, Green D, Font A, Priestman M, Hansell A, Fuller G, Tremper A, Jephcote C, Gulliver J, Hibbs L, Green D, Font A, Hansell A, Fuller G, Priestman Met al., 2022, Sources of particle number concentration and noise near London Gatwick Airport, Environment International, Vol: 161, ISSN: 0160-4120

There is increasing evidence of potential health impacts from both aircraft noise and aircraft-associated ultrafine particles (UFP). Measurements of noise and UFP are however scarce near airports and so their variability and relationship are not well understood. Particle number size distributions and noise levels were measured at two locations near Gatwick airport (UK) in 2018–19 with the aim to characterize particle number concentrations (PNC) and link PNC sources, especially UFP, with noise. Positive Matrix Factorization was used on particle number size distribution to identify these sources. Mean PNC (7500–12,000 p cm−3) were similar to those measured close to a highly trafficked road in central London. Peak PNC (94,000 p cm−3) were highest at the site closer to the runway. The airport source factor contributed 17% to the PNC at both sites and the concentrations were greatest when the respective sites were downwind of the runway. However, the main source of PNC was associated with traffic emissions. At both sites noise levels were above the recommendations by the WHO (World Health Organisation). Regression models of identified UFP sources and noise suggested that the largest source of noise (LAeq-1hr) above background was associated with sources of fresh traffic and urban UFP depending on the site. Noise and UFP correlations were moderate to low suggesting that UFP are unlikely to be an important confounder in epidemiological studies of aircraft noise and health. Correlations between UFP and noise were affected by meteorological factors, which need to be considered in studies of short-term associations between aircraft noise and health.

Journal article

Green D, 2022, Source attribution and quantification of atmospheric nickel concentrations in an industrial area in the United Kingdom (UK), Environmental Pollution, Vol: 293, Pages: 1-10, ISSN: 0269-7491

Pontardawe in South Wales, United Kingdom (UK), consistently has the highest concentrations of nickel (Ni) in PM10 in the UK and repeatedly breaches the 20 ng m−3 annual mean EU target value. Several local industries use Ni in their processes. To assist policy makers and regulators in quantifying the relative Ni contributions of these industries and developing appropriate emission reduction approaches, the hourly concentrations of 23 elements were measured using X-ray fluorescence alongside meteorological variables and black carbon during a four-week campaign in November–December 2015. Concentrations of Ni ranged between 0 and 2480 ng m−3 as hourly means. Positive Matrix Factorization (PMF) was used to identify sources contributing to measured elements. Cluster analysis of bivariate polar plots of those factors containing Ni in their profile was further used to quantify the industrial processes contributing to ambient PM10 concentrations. Two sources were identified to contribute to Ni concentrations, stainless-steel (which contributed to 10% of the Ni burden) and the Ni refinery (contributing 90%). From the stainless-steel process, melting activities were responsible for 66% of the stainless-steel factor contribution.

Journal article

Desouza CD, Marsh DJ, Beevers SD, Molden N, Green DCet al., 2021, A spatial and fleet disaggregated approach to calculating the NOX emissions inventory for non-road mobile machinery in London, Atmospheric Environment: X, Vol: 12, Pages: 1-8, ISSN: 2590-1621

The latest London atmospheric emissions inventory (2016), which is calculated using fuel consumption and construction employment, estimates that, the construction sector contributes 34% of the total PM10 emissions (the largest source), and 7% of the total NOX emissions (5th largest source). These contribute significantly to NO2 and PM2.5 pollution problems in London, which is a major concern for public health. Real-world emission factors from tail-pipe measurements were coupled to a register for construction machinery, to develop a novel ‘spatial and fleet disaggregated’ emissions inventory for the construction sector in London. This method estimated 1294 tonnes of NOX in 2018 and 1578 tonnes of NOX in 2019 from non-road mobile machinery in the construction sector, approximately 55% and 45% lower for 2018 and 2019 respectively, than the current (2016) London atmospheric emissions inventory (2850 tonnes). However, compared to the current London atmospheric emissions inventory, the new NOX emissions are higher in central London, under-estimating the importance of this source in central London. The fleet-disaggregated emissions inventory enables potential policy to be developed by focusing on high-emitters registered on the London database. As a demonstration, two emission abatement scenarios were modelled – first: by retrofitting older generators with a SCR-DPF system, a potential 53% reduction in overall NOX emissions was predicted from all NRMM; and second: by accelerating the excavator fleet-turnover – a more modest 2-tonne reduction in overall NOX emissions was predicted from all NRMM in London.

Journal article

Ciupek K, Quincey P, Green DC, Butterfield D, Fuller GWet al., 2021, Challenges and policy implications of long-term changes in mass absorption cross-section derived from equivalent black carbon and elemental carbon measurements in London and south-east England in 2014-2019, Environmental Science: Processes and Impacts, Vol: 23, Pages: 1949-1960, ISSN: 2050-7895

Determining the concentration of carbonaceous particles in ambient air is important for climate modelling, source attribution and air quality management. This study presents the difficulties associated with the interpretation of apparent long-term changes in the mass absorption cross section (MAC) of carbonaceous particles in London and south-east England based on equivalent black carbon (eBC) and elemental carbon (EC) measurements between 2014 and 2019. Although these two measurement techniques were used to determine the concentration of carbonaceous aerosols, the concentrations of eBC and EC changed at different rates at all sites, and exhibited different long-term trends. eBC measurements obtained using aethalometer instruments for traffic and urban background sites demonstrated consistent trends, showing decreases in concentrations of up to −12.5% y−1. The EC concentrations showed no change at the urban background location, a similar change to eBC at the traffic site and a significant upward trend of +10% y−1 was observed at the rural site. Despite these differences, the trends in the MAC values decreased at all sites in a similar way, with rates of change from −5.5% y−1 to −10.1% y−1. The different trends and magnitudes of change for the eBC and EC concentrations could lead to uncertainty in quantifying the efficacy of intervention measures and to different conclusions for policy making. This paper provides possible explanations of the observed decrease in MAC values over time.

Journal article

Weiss D, Resongle E, harrison R, Dietze V, Green D, Tremper A, Ochoa Ret al., 2021, Strong evidence for the continued contribution of lead deposited during the 20th century to the atmospheric environment of today, Proceedings of the National Academy of Sciences of USA, Vol: 118, ISSN: 0027-8424

Although leaded gasoline was banned at the end of the last century, lead (Pb) remains significantly enriched in airborne particles in large cities. The remobilization of historical Pb deposited in soils from atmospheric removal has been suggested as an important source providing evidence for the hypothetical long-term persistency of lead, and possibly other pollutants, in the urban environment. Here, we present data on Pb isotopic composition in airborne particles collected in London (2014 to 2018), which provide strong support that lead deposited via gasoline combustion still contributes significantly to the lead burden in present-day London. Lead concentration and isotopic signature of airborne particles collected at a heavily trafficked site did not vary significantly over the last decade, suggesting that sources remained unchanged. Lead isotopic composition of airborne particles matches that of road dust and topsoils and can only be explained with a significant contribution (estimate of 32 ± 10 to 43 ± 9% based on a binary mixing model) of Pb from leaded gasoline. The lead isotopes furthermore suggest significant contributions from nonexhaust traffic emissions, even though isotopic signatures of anthropogenic sources are increasingly overlapping. Lead isotopic composition of airborne particles collected at building height shows a similar signature to that collected at street level, suggesting effective mixing of lead within the urban street canyon. Our results have important implications on the persistence of Pb in urban environments and suggest that atmospheric Pb reached a baseline in London that is difficult to decrease further with present policy measures.

Journal article

Danko D, Bezdan D, Afshin EE, Ahsanuddin S, Bhattacharya C, Butler DJ, Chng KR, Donnellan D, Hecht J, Jackson K, Kuchin K, Karasikov M, Lyons A, Mak L, Meleshko D, Mustafa H, Mutai B, Neches RY, Ng A, Nikolayeva O, Nikolayeva T, Png E, Ryon KA, Sanchez JL, Shaaban H, Sierra MA, Thomas D, Young B, Abudayyeh OO, Alicea J, Bhattacharyya M, Blekhman R, Castro-Nallar E, Cañas AM, Chatziefthimiou AD, Crawford RW, De Filippis F, Deng Y, Desnues C, Dias-Neto E, Dybwad M, Elhaik E, Ercolini D, Frolova A, Gankin D, Gootenberg JS, Graf AB, Green DC, Hajirasouliha I, Hastings JJA, Hernandez M, Iraola G, Jang S, Kahles A, Kelly FJ, Knights K, Kyrpides NC, Łabaj PP, Lee PKH, Leung MHY, Ljungdahl PO, Mason-Buck G, McGrath K, Meydan C, Mongodin EF, Moraes MO, Nagarajan N, Nieto-Caballero M, Noushmehr H, Oliveira M, Ossowski S, Osuolale OO, Özcan O, Paez-Espino D, Rascovan N, Richard H, Rätsch G, Schriml LM, Semmler T, Sezerman OU, Shi L, Shi T, Siam R, Song LH, Suzuki H, Court DS, Tighe SW, Tong X, Udekwu KI, Ugalde JA, Valentine B, Vassilev DI, Vayndorf EM, Velavan TP, Wu J, Zambrano MM, Zhu J, Zhu S, Mason CE, International MetaSUB Consortiumet al., 2021, A global metagenomic map of urban microbiomes and antimicrobial resistance, Cell, Vol: 184, Pages: 3376-3393.e17, ISSN: 0092-8674

We present a global atlas of 4,728 metagenomic samples from mass-transit systems in 60 cities over 3 years, representing the first systematic, worldwide catalog of the urban microbial ecosystem. This atlas provides an annotated, geospatial profile of microbial strains, functional characteristics, antimicrobial resistance (AMR) markers, and genetic elements, including 10,928 viruses, 1,302 bacteria, 2 archaea, and 838,532 CRISPR arrays not found in reference databases. We identified 4,246 known species of urban microorganisms and a consistent set of 31 species found in 97% of samples that were distinct from human commensal organisms. Profiles of AMR genes varied widely in type and density across cities. Cities showed distinct microbial taxonomic signatures that were driven by climate and geographic differences. These results constitute a high-resolution global metagenomic atlas that enables discovery of organisms and genes, highlights potential public health and forensic applications, and provides a culture-independent view of AMR burden in cities.

Journal article

Leung MHY, Tong X, Bøifot KO, Bezdan D, Butler DJ, Danko DC, Gohli J, Green DC, Hernandez MT, Kelly FJ, Levy S, Mason-Buck G, Nieto-Caballero M, Syndercombe-Court D, Udekwu K, Young BG, Mason CE, Dybwad M, Lee PKHet al., 2021, Characterization of the public transit air microbiome and resistome reveals geographical specificity, Microbiome, Vol: 9, ISSN: 2049-2618

BACKGROUND: The public transit is a built environment with high occupant density across the globe, and identifying factors shaping public transit air microbiomes will help design strategies to minimize the transmission of pathogens. However, the majority of microbiome works dedicated to the public transit air are limited to amplicon sequencing, and our knowledge regarding the functional potentials and the repertoire of resistance genes (i.e. resistome) is limited. Furthermore, current air microbiome investigations on public transit systems are focused on single cities, and a multi-city assessment of the public transit air microbiome will allow a greater understanding of whether and how broad environmental, building, and anthropogenic factors shape the public transit air microbiome in an international scale. Therefore, in this study, the public transit air microbiomes and resistomes of six cities across three continents (Denver, Hong Kong, London, New York City, Oslo, Stockholm) were characterized. RESULTS: City was the sole factor associated with public transit air microbiome differences, with diverse taxa identified as drivers for geography-associated functional potentials, concomitant with geographical differences in species- and strain-level inferred growth profiles. Related bacterial strains differed among cities in genes encoding resistance, transposase, and other functions. Sourcetracking estimated that human skin, soil, and wastewater were major presumptive resistome sources of public transit air, and adjacent public transit surfaces may also be considered presumptive sources. Large proportions of detected resistance genes were co-located with mobile genetic elements including plasmids. Biosynthetic gene clusters and city-unique coding sequences were found in the metagenome-assembled genomes. CONCLUSIONS: Overall, geographical specificity transcends multiple aspects of the public transit air microbiome, and future efforts on a global scale are warranted to in

Journal article

Bressi M, Cavalli F, Putaud JP, Fröhlich R, Petit J-E, Aas W, Äijälä M, Alastuey A, Allan JD, Aurela M, Berico M, Bougiatioti A, Bukowiecki N, Canonaco F, Crenn V, Dusanter S, Ehn M, Elsasser M, Flentje H, Graf P, Green DC, Heikkinen L, Hermann H, Holzinger R, Hueglin C, Keernik H, Kiendler-Scharr A, Kubelová L, Lunder C, Maasikmets M, Makeš O, Malaguti A, Mihalopoulos N, Nicolas JB, O'Dowd C, Ovadnevaite J, Petralia E, Poulain L, Priestman M, Riffault V, Ripoll A, Schlag P, Schwarz J, Sciare J, Slowik J, Sosedova Y, Stavroulas I, Teinemaa E, Via M, Vodička P, Williams PI, Wiedensohler A, Young DE, Zhang S, Favez O, Minguillón MC, Prevot ASHet al., 2021, A European aerosol phenomenology - 7: High-time resolution chemical characteristics of submicron particulate matter across Europe, Atmospheric Environment: X, Vol: 10, Pages: 1-16, ISSN: 2590-1621

Similarities and differences in the submicron atmospheric aerosol chemical composition are analyzed from a unique set of measurements performed at 21 sites across Europe for at least one year. These sites are located between 35 and 62°N and 10° W – 26°E, and represent various types of settings (remote, coastal, rural, industrial, urban). Measurements were all carried out on-line with a 30-min time resolution using mass spectroscopy based instruments known as Aerosol Chemical Speciation Monitors (ACSM) and Aerosol Mass Spectrometers (AMS) and following common measurement guidelines. Data regarding organics, sulfate, nitrate and ammonium concentrations, as well as the sum of them called non-refractory submicron aerosol mass concentration ([NR-PM1]) are discussed. NR-PM1 concentrations generally increase from remote to urban sites. They are mostly larger in the mid-latitude band than in southern and northern Europe. On average, organics account for the major part (36–64%) of NR-PM1 followed by sulfate (12–44%) and nitrate (6–35%). The annual mean chemical composition of NR-PM1 at rural (or regional background) sites and urban background sites are very similar. Considering rural and regional background sites only, nitrate contribution is higher and sulfate contribution is lower in mid-latitude Europe compared to northern and southern Europe. Large seasonal variations in concentrations (μg/m³) of one or more components of NR-PM1 can be observed at all sites, as well as in the chemical composition of NR-PM1 (%) at most sites. Significant diel cycles in the contribution to [NR-PM1] of organics, sulfate, and nitrate can be observed at a majority of sites both in winter and summer. Early morning minima in organics in concomitance with maxima in nitrate are common features at regional and urban background sites. Daily variations are much smaller at a number of coastal and rural sites. Looking at NR-PM1 chemical composition as a func

Journal article

Hicks W, Beevers S, Tremper A, Stewart G, Priestman M, Kelly F, Lanoisellé M, Lowry D, Green Det al., 2021, Quantification of non-exhaust particulate matter traffic emissions and the impact of COVID-19 lockdown at London Marylebone Road, Atmosphere, Vol: 12, Pages: 1-19, ISSN: 2073-4433

This research quantifies current sources of non-exhaust particulate matter traffic emissions in London using simultaneous, highly time-resolved, atmospheric particulate matter mass and chemical composition measurements. The measurement campaign ran at Marylebone Road (roadside) and Honor Oak Park (background) urban monitoring sites over a 12-month period between 1 September 2019 and 31 August 2020. The measurement data has been used to determine the traffic increment (roadside – background) and covers a range of meteorological conditions, seasons and driving styles, as well as the influence of the COVID-19 ‘lockdown’ on non-exhaust concentrations. Non-exhaust PM10 concentrations are calculated using chemical tracer scaling factors for brake wear (barium), tyre wear (zinc) and resuspension (silicon) and as average vehicle fleet non-exhaust emission factors, using a CO2 ‘dilution approach’. The effect of lockdown, which saw a 32% reduction in traffic volume and a 15% increase in average speed on Marylebone Road, resulted in lower PM10 and PM2.5 traffic increments and brake wear concentrations, but similar tyre and resuspension concentrations, confirming that factors that determine non-exhaust emissions are complex. Brake wear was found to be the highest average non-exhaust emission source. In addition, results indicated that non-exhaust emission factors are dependent upon speed and road surface wetness conditions. Further statistical analysis incorporating a wider variability in vehicle mix, speeds and meteorological conditions, as well as advanced source apportionment of the PM measurement data, will be undertaken to enhance our understanding of these important vehicle sources.

Journal article

Analitis A, Barratt B, Green D, Beddows A, Samoli E, Schwartz J, Katsouyanni Ket al., 2020, Prediction of PM2.5 concentrations at the locations of monitoring sites measuring PM10 and NOx, using generalized additive models and machine learning methods: A case study in London, ATMOSPHERIC ENVIRONMENT, Vol: 240, ISSN: 1352-2310

Journal article

Font A, Tremper AH, Lin C, Priestman M, Marsh D, Woods M, Heal MR, Green DCet al., 2020, Air quality in enclosed railway stations: Quantifying the impact of diesel trains through deployment of multi-site measurement and random forest modelling, ENVIRONMENTAL POLLUTION, Vol: 262, ISSN: 0269-7491

Journal article

Desouza CD, Marsh DJ, Beevers SD, Molden N, Green DCet al., 2020, Real-world emissions from non-road mobile machinery in London, Atmospheric Environment, Vol: 223, ISSN: 1352-2310

The 2016 London atmospheric emissions inventory estimates that, the construction sector contributes 34% of the total PM10 and 7% of the total NOX – the largest and 5th largest sources, respectively. Recent on-road light duty diesel vehicle emission tests have shown significant differences between real-world NOX emissions compared with results from laboratory based regulatory tests. The aim of this study was therefore to quantify the ‘real-world’ tail-pipe NOX, CO2, and particle emissions, for 30 of the most commonly used construction machines in London under normal working conditions. The highest NOX emissions (g/kWh) were from theolder engines (Stage III-A ~4.88 g/kWh and III-B ~4.61 g/kWh), these were reduced significantly (~78%) in the newer (Stage IV ~1.05 g/kWh) engines due to more advanced engine management systems and exhaust after treatment. One Stage IV machine emitted NOX similar to a Stage III-B machine, the failure of this SCR was only detectable using PEMS as no warning was given by the machine. Higher NOX conformity factors were observed for Stage IV machines, due to the lower NOX emission standards, which these machines must adhere to. On average, Stage III-B machines (~525 g/kWh) emitted the lowest levels of CO2 emissions, compared to Stage III-A (~875 g/kWh) and Stage IV (~575 g/kWh) machines. Overall, a statistically significant (~41%) decrease was observed in the CO2 emissions (g/kWh) between Stage III-A and III-B machines, while no statistically significant difference was found between Stage III-B and IV machines. Particle mass measurements, which were only measured from generators, showed that generators of all engine sizes were within their respective Stage III-A emission standards. A 95% reduction in NOX and 2 orders of magnitude reduction in particle number was observed for a SCR-DPF retrofitted generator, compared to the same generator prior to exhaust gas after-treatment strategy.

Journal article

Zhang T, Wooster M, Green DC, Main Bet al., 2020, A Mathematical Approach to Merging Data from Different Trace Gas/Particulate Sensors Having Dissimilar (T90) Response Times: Application to Fire Emission Factor Determination, AEROSOL AND AIR QUALITY RESEARCH, Vol: 20, Pages: 281-290, ISSN: 1680-8584

Journal article

Rivas I, Beddows DCS, Amato F, Green DC, Järvi L, Hueglin C, Reche C, Timonen H, Fuller GW, Niemi JV, Pérez N, Aurela M, Hopke PK, Alastuey A, Kulmala M, Harrison RM, Querol X, Kelly FJet al., 2020, Source apportionment of particle number size distribution in urban background and traffic stations in four European cities, Environment International, Vol: 135, ISSN: 0160-4120

Ultrafine particles (UFP) are suspected of having significant impacts on health. However, there have only been a limited number of studies on sources of UFP compared to larger particles. In this work, we identified and quantified the sources and processes contributing to particle number size distributions (PNSD) using Positive Matrix Factorization (PMF) at six monitoring stations (four urban background and two street canyon) from four European cities: Barcelona, Helsinki, London, and Zurich. These cities are characterised by different meteorological conditions and emissions. The common sources across all stations were Photonucleation, traffic emissions (3 sources, from fresh to aged emissions: Traffic nucleation, Fresh traffic - mode diameter between 13 and 37 nm, and Urban - mode diameter between 44 and 81 nm, mainly traffic but influenced by other sources in some cities), and Secondary particles. The Photonucleation factor was only directly identified by PMF for Barcelona, while an additional split of the Nucleation factor (into Photonucleation and Traffic nucleation) by using NOx concentrations as a proxy for traffic emissions was performed for all other stations. The sum of all traffic sources resulted in a maximum relative contributions ranging from 71 to 94% (annual average) thereby being the main contributor at all stations. In London and Zurich, the relative contribution of the sources did not vary significantly between seasons. In contrast, the high levels of solar radiation in Barcelona led to an important contribution of Photonucleation particles (ranging from 14% during the winter period to 35% during summer). Biogenic emissions were a source identified only in Helsinki (both in the urban background and street canyon stations), that contributed importantly during summer (23% in urban background). Airport emissions contributed to Nucleation particles at urban background sites, as the highest concentrations of this source took place when the wind

Journal article

Barratt BM, Fuller GW, Kelly FJ, Priestman M, Tremper AH, Green DCet al., 2020, PM2.5 on the London Underground, Environment International, Vol: 134, ISSN: 0160-4120

Introduction: Despite the London Underground (LU) handling on average 2.8 million passenger journeys per day, the characteristics and potential health effects of the elevated concentrations of metal-rich PM2.5 found in this subway system are not well understood. Methods: Spatial monitoring campaigns were carried out to characterise the health-relevant chemical and physical properties of PM2.5 across the LU network, including diurnal and day-to-day variability and spatial distribution (above ground, depth below ground and subway line). Population-weighted station PM2.5 rankings were produced to understand the relative importance of concentrations at different stations and on different lines. Results: The PM2.5 mass in the LU (mean 88 μg m−3, median 28 μg m−3) was greater than at ambient background locations (mean 19 μg m−3, median 14 μg m−3) and roadside environments in central London (mean 22 μg m−3, median 14 μg m−3). Concentrations varied between lines and locations, with the deepest and shallowest submerged lines being the District (median 4 μg m−3) and Victoria (median 361 μg m−3 but up to 885 μg m−3). Broadly in agreement with other subway systems around the world, sampled LU PM2.5 comprised 47% iron oxide, 7% elemental carbon, 11% organic carbon, and 14% metallic and mineral oxides. Although a relationship between line depth and air quality inside the tube trains was evident, there were clear influences relating to the distance from cleaner outside air and the exchange with cabin air when the doors open. The passenger population-weighted exposure analysis demonstrated a method to identify stations that should be prioritised for remediation to improve air quality. Conclusion: PM2.5 concentrations in the LU are many times higher than in other London transport Environments. Failure to include this environment in epidemiological studies of the relationship between PM2.5 and health in

Journal article

Saunders BM, Smith JD, Smith TEL, Green DC, Barratt Bet al., 2019, Spatial variability of fine particulate matter pollution (PM2.5) on the London Underground network, URBAN CLIMATE, Vol: 30, ISSN: 2212-0955

Journal article

Freney E, Zhang Y, Croteau P, Amodeo T, Williams L, Truong F, Petit J-E, Sciare J, Sarda-Esteve R, Bonnaire N, Arumae T, Aurela M, Bougiatioti A, Mihalopoulos N, Coz E, Artinano B, Crenn V, Elste T, Heikkinen L, Poulain L, Wiedensohler A, Herrmann H, Priestman M, Alastuey A, Stavroulas I, Tobler A, Vasilescu J, Zanca N, Canagaratna M, Carbone C, Flentje H, Green D, Maasikmets M, Marmureanu L, Minguillon MC, Prevot ASH, Gros V, Jayne J, Favez Oet al., 2019, The second ACTRIS inter-comparison (2016) for Aerosol Chemical Speciation Monitors (ACSM): Calibration protocols and instrument performance evaluations, AEROSOL SCIENCE AND TECHNOLOGY, ISSN: 0278-6826

Journal article

Green DC, Fuller GW, 2019, Evaluation of tire wear contribution to PM2.5 in urban environments, Atmosphere, Vol: 10

Vehicle-related particulate matter (PM) emissions may arise from both exhaust andnon-exhaust mechanisms, such as brake wear, tire wear, and road pavement abrasion, each ofwhich may be emitted directly and indirectly through resuspension of settled road dust. Severalresearchers have indicated that the proportion of PM2.5 attributable to vehicle traffic will increasingly come from non-exhaust sources. Currently, very little empirical data is available to characterize tire and road wear particles (TRWP) in the PM2.5 fraction. As such, this study was undertaken to quantify TRWP in PM2.5 at roadside locations in urban centers including London, Tokyo and Los Angeles, where vehicle traffic is an important contributor to ambient air PM. The samples were analyzed using validated chemical markers for tire tread polymer based on a pyrolysis technique. Results indicated that TRWP concentrations in the PM2.5 fraction were low, with averages ranging from < 0.004 to 0.10 g/m3, representing an average contribution to total PM2.5 of 0.27%. The TRWP levels in PM2.5 were significantly different between the three cities, with significant differences between London and Los Angeles and Tokyo and Los Angeles. There was no significant correlation between TRWP in PM2.5 and traffic count. This study provides an initial dataset to understand potential human exposure to airborne TRWP and the potential contribution of this non-exhaust emission source to total PM2.5.

Journal article

Warren E, Charlton-perez C, Kotthaus S, Marenco F, Ryder C, Johnson B, Green D, Lean H, Ballard S, Grimmond Set al., 2019, Observed aerosol characteristics to improve forward-modelled attenuated backscatter in urban areas, ATMOSPHERIC ENVIRONMENT, ISSN: 1352-2310

Numerical weather prediction (NWP) models often parameterise aerosols to reduce computational needs, while aiming to accurately capture their impact adequately. Increasingly, aerosols are monitored in-situ directly and/or indirectly (e.g. by automatic lidars and ceilometers, ALC). ALC measure the aerosol optical characteristic of attenuated backscatter. This can also be estimated using forward models that combine forecast aerosol and relative humidity to parameterise aerosol physical and optical characteristics. The aerFO is one such forward model, designed to use Met Office NWP model output and parameterisations from the MURK visibility scheme. Given the aerFO-MURK scheme link, assessing the aerFO and its output could therefore be used to inform future developments of the MURK scheme. To identify which parameterised physical and optical aerosol characteristics in the scheme are the most critical in urban settings, aerFO is driven with different in-situ aerosol observations at a background site in central London. Estimated attenuated backscatter is then assessed against ALC observations. It is shown that the original MURK scheme parameterisation underestimates the variance of both dry mean volume radius and total number concentration. Representing both the accumulation and coarse mode aerosols in the aerFO reduces the median bias error of estimated attenuated backscatter by 69.1%. Providing more realistic temporal (monthly to hourly) variability of relative mass for different species leads to little improvement, compared to using monthly climatological means. Numerical experiments show that having more realistic estimates of number concentration is more important than providing more accurate values of the dry mean volume radius for the accumulation mode. Hence, improving the parameterisations for number concentration should be a main focus for further development of the MURK scheme. To estimate aerosol attenuated backscatter, the aerFO requires an extinction to back

Journal article

Tremper AH, Font A, Priestman M, Hamad SH, Chung T-C, Pribadi A, Brown RJC, Goddard SL, Grassineau N, Petterson K, Kelly FJ, Green DCet al., 2018, Field and laboratory evaluation of a high time resolution x-ray fluorescence instrument for determining the elemental composition of ambient aerosols, ATMOSPHERIC MEASUREMENT TECHNIQUES, Vol: 11, Pages: 3541-3557, ISSN: 1867-1381

Journal article

McEneff GL, Murphy B, Webb T, Wood D, Irlam R, Mills J, Green D, Barron LPet al., 2018, Sorbent film-coated passive samplers for explosives vapour detection Part A, Materials Optimisation and Integration with Analytical Technologies, Vol: 8, Pages: 1-13, ISSN: 2045-2322

A new thin-film passive sampler is presented as a low resource dependent and discrete continuous monitoring solution for explosives-related vapours. Using 15 mid-high vapour pressure explosives-related compounds as probes, combinations of four thermally stable substrates and six film-based sorbents were evaluated. Meta-aramid and phenylene oxide-based materials showed the best recoveries from small voids (~70%). Analysis was performed using liquid chromatography-high resolution accurate mass spectrometry which also enabled tentative identification of new targets from the acquired data. Preliminary uptake kinetics experiments revealed plateau concentrations on the device were reached between 3–5 days. Compounds used in improvised explosive devices, such as triacetone triperoxide, were detected within 1 hour and were stably retained by the sampler for up to 7 days. Sampler performance was consistent for 22 months after manufacture. Lastly, its direct integration with currently in-service explosives screening equipment including ion mobility spectrometry and thermal desorption mass spectrometry is presented. Following exposure to several open environments and targeted interferences, sampler performance was subsequently assessed and potential interferences identified. High-security building and area monitoring for concealed explosives using such cost-effective and discrete passive samplers can add extra assurance to search routines while minimising any additional burden on personnel or everyday site operation.

Journal article

McEneff GL, Richardson A, Webb T, Wood D, Murphy B, Irlam R, Mills J, Green D, Barron LPet al., 2018, Sorbent film-coated passive samplers for explosives vapour detection Part B, Deployment in Semi-Operational Environments and Alternative Applications, Vol: 8, Pages: 1-13, ISSN: 2045-2322

The application of new sorbent-film coated passive samplers for capture of bulk commercial and military explosives vapours in operationally relevant spaces such as luggage, rooms, vehicles and shipping containers is presented. Samplers were easily integrated with in-service detection technologies with little/no sample preparation required. Ethylene glycol dinitrate (EGDN) was detected within 4 h in a container holding a suitcase packed with 0.2 kg Perunit 28E. Within a 22,000 dm3 room, 1 kg of concealed Seguridad was detected within 24 h and in an adjoining room within 7 days. Exposed samplers also successfully captured components of 1 kg TNT after 72 h and 1 kg concealed Perunit 28E after 6 h in both a furnished room and a large, partially filled shipping container. For the latter, samplers captured detectable residues outside the container after 24 h and were stable during wet weather for 72 h. A one-week trial at three operationally relevant venues including a university, a theatre and a government building revealed a nuisance positive rate of <1.4% (n = 72). Finally, two alternative applications are presented for extraction of liquid samples and use a particulate contact swab showing flexibility for a range of different search activities.

Journal article

Ots R, Heal MR, Young DE, Williams LR, Allan JD, Nemitz E, Di Marco C, Detournay A, Xu L, Ng NL, Coe H, Herndon SC, Mackenzie IA, Green DC, Kuenen JJP, Reis S, Vieno Met al., 2018, Modelling carbonaceous aerosol from residential solid fuel burning with different assumptions for emissions, ATMOSPHERIC CHEMISTRY AND PHYSICS, Vol: 18, Pages: 4497-4518, ISSN: 1680-7316

Journal article

Wooster MJ, Gaveau DLA, Salim MA, Zhang T, Xu W, Green DC, Huijnen V, Murdiyarso D, Gunawan D, Borchard N, Schirrmann M, Main B, Sepriando Aet al., 2018, New Tropical Peatland Gas and Particulate Emissions Factors Indicate 2015 Indonesian Fires Released Far More Particulate Matter (but Less Methane) than Current Inventories Imply, REMOTE SENSING, Vol: 10

Journal article

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