Publications by authors named "Roy M Harrison"

117 Publications

Chemical source profiles of fine particles for five different sources in Delhi.

Chemosphere 2021 Jul 9;274:129913. Epub 2021 Feb 9.

Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India.

Increasing emissions from sources such as construction and burning of biomass from crop residues, roadside and municipal solid waste have led to a rapid increase in the atmospheric concentrations of fine particulate matter (≤2.5 μm; PM) over many Indian cities. Analyses of their chemical profiles are important for receptor models to accurately estimate the contributions from different sources. We have developed chemical source profiles for five important pollutant sources - construction (CON), paved road dust (PRD), roadside biomass burning (RBB), solid waste burning (SWB), and crop residue burning (CPB) - during three intensive campaigns (winter, summer and post-monsoon) in and around Delhi. We obtained chemical characterisations of source profiles incorporating carbonaceous material such as organic carbon (OC) and elemental carbon (EC), water-soluble ions (F, Cl, NO, NO, SO, PO, Na and NH), and elements (Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br, Rb, Sr, Ba, and Pb). CON was dominated by the most abundant elements, K, Si, Fe, Al, and Ca. PRD was also dominated by crustal elements, accounting for 91% of the total analysed elements. RBB, SWB and CPB profiles were dominated by organic matter, which accounted for 94%, 86.2% and 86% of the total PM, respectively. The database of PM emission profiles developed from the sources investigated can be used to assist source apportionment studies for accurate quantification of the causes of air pollution and hence assist governmental bodies in formulating relevant countermeasures.
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http://dx.doi.org/10.1016/j.chemosphere.2021.129913DOI Listing
July 2021

On the nature of polycyclic aromatic hydrocarbons associated with sporting walkways dust: Concentrations, sources and relative health risk.

Sci Total Environ 2021 Mar 22;781:146540. Epub 2021 Mar 22.

Department of Environmental Sciences, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, P.O. Box 80208, Jeddah 21589, Saudi Arabia; Division of Environmental Health & Risk Management, School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom. Electronic address:

Sporting walkways (SW) are a new innovation which may prove popular in many cities. As there is currently no information on possible health risks associated with their use, concentrations of polycyclic aromatic hydrocarbons (PAHs) associated with deposited dust sampled on SW in Jeddah, Saudi Arabia, have been measured and interpreted in relation to sources and cancer risk. The average ∑PAHs (16 compounds) ranged between 1357 ng/g in residential areas and 3764 ng/g in central urban areas, with suburban areas between. The congener profile and diagnostic ratios of PAHs indicate a predominant source associated with petroleum combustion (pyrogenic source), most probably vehicular emissions. Carcinogenic potential is estimated from the sum of carcinogenic compound concentrations weighted by their individual potency relative to benzo(a)pyrene, and is found to be similar to household dust sampled in the same city, and lower than many other indoor and outdoor (road) dusts sampled across the world.
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http://dx.doi.org/10.1016/j.scitotenv.2021.146540DOI Listing
March 2021

Ubiquitous atmospheric contamination by tobacco smoke: Nicotine and a new marker for tobacco smoke-derived particulate matter, nicotelline.

Environ Int 2021 05 6;150:106417. Epub 2021 Feb 6.

Division of Cardiology, Clinical Pharmacology Program, Department of Medicine, University of California, San Francisco, CA 94143, United States.

Second Hand Smoke (SHS) has always been primarily linked with indoor pollution. To date nicotine was the favoured marker for SHS alongside measurements of particulate matter (PM) levels. As nicotine is mainly found in the gas-phase and reactive in the outdoor environment it is not ideal as a marker for the SHS-driven particulate component in PM. Nicotelline, a minor tobacco alkaloid that is stable, found almost exclusively in the particle phase and easy to quantify even at low concentrations, is being proposed as a better marker. It is the first study using bisulfate-treated quartz fiber filters to show that airborne nicotine (gas+particle phase) is directly proportional to airborne nicotelline in countries that have different climates. The analytical method developed has been validated to show that the use of untreated filters is suitable for the quantification of nicotelline even at low concentrations. Although nicotelline exhibits a seasonal and geographical variation, this is the first comprehensive study which demonstrates the ubiquitous presence of nicotelline in PM from outdoor air samples collected in the USA (0.1-285.6 pgm), UK (2.3-9.1 pgm), Hong Kong (3.8-109.3 pgm) and Malta (4.2-280.8 pgm). From the nicotelline apportionment factor of 1589 ng/mg of tobacco smoke PM we estimate the fraction of outdoor airborne PM derived from SHS to be in the range of 0.03-0.08%. While it is unlikely for tobacco smoke-related toxics in outdoor PM to be considered a major health hazard, in heavily polluted microenvironments this marker would be useful in tracing the presence of SHS and emerging Third Hand Smoke components that form or are found in airborne and settled PM that could induce serious health effects.
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http://dx.doi.org/10.1016/j.envint.2021.106417DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7987222PMC
May 2021

More mileage in reducing urban air pollution from road traffic.

Environ Int 2021 04 6;149:106329. Epub 2021 Feb 6.

Division of Environmental Health and Risk Management, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.

Road traffic emissions are considered a major contributor to urban air pollution, but clean air actions have led to a huge reduction in emissions per vehicle. This raises a pressing question on the potential to further reduce road traffic emissions to improve air quality. Here, we analysed ~11 million real-world data to estimate the contribution of road traffic to roadside and urban concentrations for several major cities. Our results confirm that road traffic remains a dominant source of nitrogen dioxide and a significant source of primary coarse particulate matter in the European cities. However, it now represents a relatively small component of overall PM at urban background locations in cities with strong controls on traffic emissions (including European cities and Beijing) and many roadside sites will exceed the WHO guideline (10 μg m annual mean) even when this source is eliminated. This suggests that further controls on traffic emissions, including the transition to a battery-electric fleet, are needed to reduce NO concentrations, but this will have limited benefit to reduce the concentration of fine particles, except in countries where the use of diesel particle filters is not mandatory. There are substantial differences between cities and the optimal solution will differ from one to another.
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http://dx.doi.org/10.1016/j.envint.2020.106329DOI Listing
April 2021

Abrupt but smaller than expected changes in surface air quality attributable to COVID-19 lockdowns.

Sci Adv 2021 01 13;7(3). Epub 2021 Jan 13.

School of Geography Earth and Environment Sciences, University of Birmingham, Birmingham B15 2TT, UK.

The COVID-19 lockdowns led to major reductions in air pollutant emissions. Here, we quantitatively evaluate changes in ambient NO, O, and PM concentrations arising from these emission changes in 11 cities globally by applying a deweathering machine learning technique. Sudden decreases in deweathered NO concentrations and increases in O were observed in almost all cities. However, the decline in NO concentrations attributable to the lockdowns was not as large as expected, at reductions of 10 to 50%. Accordingly, O increased by 2 to 30% (except for London), the total gaseous oxidant (O = NO + O) showed limited change, and PM concentrations decreased in most cities studied but increased in London and Paris. Our results demonstrate the need for a sophisticated analysis to quantify air quality impacts of interventions and indicate that true air quality improvements were notably more limited than some earlier reports or observational data suggested.
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http://dx.doi.org/10.1126/sciadv.abd6696DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7806219PMC
January 2021

Insights into air pollution chemistry and sulphate formation from nitrous acid (HONO) measurements during haze events in Beijing.

Faraday Discuss 2021 Mar 7;226:223-238. Epub 2020 Dec 7.

School of Geography, Earth and Environmental Sciences, University of Birmingham, UK.

Wintertime urban air pollution in many global megacities is characterised by episodic rapid increase in particulate matter concentrations associated with elevated relative humidity - so-called haze episodes, which have become characteristic of cities such as Beijing. Atmospheric chemistry within haze combines gas- and condensed-phase chemical processes, leading to the growth in secondary species such as sulphate aerosols. Here, we integrate observations of reactive gas phase species (HONO, OH, NO) and time-resolved aerosol composition, to explore observational constraints on the mechanisms responsible for sulphate growth during the onset of haze events. We show that HONO abundance is dominated by established fast gas-phase photochemistry, but the consideration of the additional formation potentially associated with condensed-phase oxidation of S species by aqueous NO leading to NO production and hence HONO release, improves agreement between observed and calculated gas-phase HONO levels. This conclusion is highly dependent upon aerosol pH, ionic strength and particularly the parameterisation employed for S(iv) oxidation kinetics, for which an upper limit is derived.
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http://dx.doi.org/10.1039/d0fd00100gDOI Listing
March 2021

An evaluation of source apportionment of fine OC and PM by multiple methods: APHH-Beijing campaigns as a case study.

Faraday Discuss 2021 Mar 26;226:290-313. Epub 2020 Nov 26.

School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK.

This study aims to critically evaluate the source apportionment of fine particles by multiple receptor modelling approaches, including carbon mass balance modelling of filter-based radiocarbon (C) data, Chemical Mass Balance (CMB) and Positive Matrix Factorization (PMF) analysis on filter-based chemical speciation data, and PMF analysis on Aerosol Mass Spectrometer (AMS-PMF) or Aerosol Chemical Speciation Monitor (ACSM-PMF) data. These data were collected as part of the APHH-Beijing (Atmospheric Pollution and Human Health in a Chinese Megacity) field observation campaigns from 10 November to 12 December in winter 2016 and from 22 May to 24 June in summer 2017. C analysis revealed the predominant contribution of fossil fuel combustion to carbonaceous aerosols in winter compared with non-fossil fuel sources, which is supported by the results from other methods. An extended Gelencsér (EG) method incorporating C data, as well as the CMB and AMS/ACSM-PMF methods, generated a consistent source apportionment for fossil fuel related primary organic carbon. Coal combustion, traffic and biomass burning POC were comparable for CMB and AMS/ACSM-PMF. There are uncertainties in the EG method when estimating biomass burning and cooking OC. The POC from cooking estimated by different methods was poorly correlated, suggesting a large uncertainty when differentiating this source type. The PM source apportionment results varied between different methods. Through a comparison and correlation analysis of CMB, PMF and AMS/ACSM-PMF, the CMB method appears to give the most complete and representative source apportionment of Beijing aerosols. Based upon the CMB results, fine aerosols in Beijing were mainly secondary inorganic ion formation, secondary organic aerosol formation, primary coal combustion and from biomass burning emissions.
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http://dx.doi.org/10.1039/d0fd00095gDOI Listing
March 2021

Airborne particulate matter.

Authors:
Roy M Harrison

Philos Trans A Math Phys Eng Sci 2020 Oct 28;378(2183):20190319. Epub 2020 Sep 28.

Division of Environmental Health and Risk Management, School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK.

Airborne particulate matter (PM) is a pollutant of concern not only because of its adverse effects on human health but because of its ability to reduce visibility and soil buildings and materials. It can be regarded as a suite of pollutants since PM covers a very wide range of particle sizes and also has a diverse chemical composition. Historically, much of the PM arose from coal burning and was measured as black smoke. However, in the second half of the twentieth century in developed countries, there was a reduction in black smoke emissions from coal burning and PM steadily became dominated by carbonaceous particles from road traffic exhaust and the secondary pollutants, ammonium salts and secondary organic carbon. This is exemplified by the composition of fine particles (referred to as PM) as measured in London, Delhi and Beijing. Steadily, as control strategies have addressed the more tractable sources of emissions, so sources previously regarded as unconventional have emerged and have been seen to make a significant contribution to airborne PM concentrations. Among these are non-exhaust particles from road traffic, cooking aerosol and wood smoke. The particle size distribution of airborne PM is hugely diverse, ranging from newly formed particles of a few nanometres in diameter through to particles of tens of micrometres in diameter. There has been a great deal of interest in ultrafine (nano) particles because of suspicions of enhanced toxicity, and as traffic emissions decrease as a source, so regional nucleation processes have become much bigger relative contributors to particle number, but not mass. This article is part of a discussion meeting issue 'Air quality, past present and future'.
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http://dx.doi.org/10.1098/rsta.2019.0319DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7536032PMC
October 2020

Neighbourhood-scale dispersion of traffic-induced ultrafine particles in central London: WRF large eddy simulations.

Environ Pollut 2020 Nov 20;266(Pt 3):115223. Epub 2020 Jul 20.

School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK; Department of Environmental Sciences, Center of Excellence in Environmental Studies, King Abdulaziz University, PO Box 80203, Jeddah, 21589, Saudi Arabia.

Traffic-generated ultrafine particles (UFPs) in the urban atmosphere have a high proportion of their composition comprised of semi-volatile compounds (SVOCs). The evaporation/condensation processes of these SVOCs can alter UFP number size distributions and play an important role in determining the fate of UFPs in urban areas. The neighbourhood-scale dispersion (over distances < 1 km) and evolution of traffic-generated UFPs for a real-world street network in central London was simulated by using the WRF-LES model (the large eddy simulation mode of the Weather Research and Forecasting modelling system) coupled with multicomponent microphysics. The neighbourhood scale dispersion of UFPs was significantly influenced by the spatial pattern of the real-world street emissions. Model output indicated the shrinkage of the peak diameter from the emitted profile to the downwind profile, due to an evaporation process during neighbourhood-scale dispersion. The dilution process and the aerosol microphysics interact with each other during the neighbourhood dispersion of UFPs, yielding model output that compares well with measurements made at a location downwind of an intense roadside source. The model captured the total SVOC concentrations well, with overestimations for gas concentrations and underestimations for particle concentrations, particularly of the lighter SVOCs. The contribution of the intense source, Marylebone Road (MR) in London, to concentrations at the downwind location (as estimated by a model scenario with emissions from MR only) is comparable with that of the rest of the street network (a scenario without emissions from MR), implying that both are important. An appreciable level of non-linearity is demonstrated for nucleation mode UFPs and medium range carbon SVOCs at the downwind receptor site.
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http://dx.doi.org/10.1016/j.envpol.2020.115223DOI Listing
November 2020

Source apportionment of fine organic carbon (OC) using receptor modelling at a rural site of Beijing: Insight into seasonal and diurnal variation of source contributions.

Environ Pollut 2020 Nov 26;266(Pt 1):115078. Epub 2020 Jun 26.

Division of Environmental Health and Risk Management, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom. Electronic address:

This study was designed to investigate the seasonal characteristics and apportion the sources of organic carbon during non-haze days (<75 μg m) and haze (≥75 μg m) events at Pinggu, a rural Beijing site. Time-resolved concentrations of carbonaceous aerosols and organic molecular tracers were measured during the winter of 2016 and summer 2017, and a Chemical Mass Balance (CMB) model was applied to estimate the average source contributions. The concentration of OC in winter is comparable with previous studies, but relatively low during the summer. The CMB model apportioned seven separate primary sources, which explained on average 73.8% on haze days and 81.2% on non-haze days of the organic carbon in winter, including vegetative detritus, biomass burning, gasoline vehicles, diesel vehicles, industrial coal combustion, residential coal combustion and cooking. A slightly lower percentage of OC was apportioned in the summer campaign with 64.5% and 78.7% accounted for. The other unapportioned OC is considered to consist of secondary organic carbon (SOC). During haze episodes in winter, coal combustion and SOC were the dominant sources of organic carbon with 23.3% and 26.2%, respectively, followed by biomass burning emissions (20%), whereas in summer, industrial coal combustion and SOC were important contributors. Diurnal contribution cycles for coal combustion and biomass burning OC showed a peak at 6-9 pm, suggesting domestic heating and cooking were the main sources of organic aerosols in this rural area. Backward trajectory analysis showed that high OC concentrations were measured when the air mass was from the south, suggesting that the organic aerosols in Pinggu were affected by both local emissions and regional transport from central Beijing and Hebei province during haze episodes. The source apportionment by CMB is compared with the results of a Positive Matrix Factorization (PMF) analysis of ACSM data for non-refractory PM, showing generally good agreement.
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http://dx.doi.org/10.1016/j.envpol.2020.115078DOI Listing
November 2020

Contribution of Water-Soluble Organic Matter from Multiple Marine Geographic Eco-Regions to Aerosols around Antarctica.

Environ Sci Technol 2020 07 21;54(13):7807-7817. Epub 2020 Jun 21.

Institute of Marine Sciences, Passeig Marítim de la Barceloneta, 37-49, Barcelona E-08003, Spain.

We present shipborne measurements of size-resolved concentrations of aerosol components across ocean waters next to the Antarctic Peninsula, South Orkney Islands, and South Georgia Island, evidencing aerosol features associated with distinct eco-regions. Nonmethanesulfonic acid Water-Soluble Organic Matter (WSOM) represented 6-8% and 11-22% of the aerosol PM mass originated in open ocean (OO) and sea ice (SI) regions, respectively. Other major components included sea salt (86-88% OO, 24-27% SI), non sea salt sulfate (3-4% OO, 35-40% SI), and MSA (1-2% OO, 11-12% SI). The chemical composition of WSOM encompasses secondary organic components with diverse behaviors: while alkylamine concentrations were higher in SI air masses, oxalic acid showed higher concentrations in the open ocean air. Our online single-particle mass spectrometry data exclude a widespread source from sea bird colonies, while the secondary production of oxalic acid and sulfur-containing organic species via cloud processing is suggested. We claim that the potential impact of the sympagic planktonic ecosystem on aerosol composition has been overlooked in past studies, and multiple eco-regions act as distinct aerosol sources around Antarctica.
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http://dx.doi.org/10.1021/acs.est.0c00695DOI Listing
July 2020

Behaviour of traffic emitted semi-volatile and intermediate volatility organic compounds within the urban atmosphere.

Sci Total Environ 2020 Jun 20;720:137470. Epub 2020 Feb 20.

Division of Environmental Health and Risk Management, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom. Electronic address:

Particulate matter originated from traffic has attracted major interest over the last few years. The semi-volatile organic component of the particles may evaporate with dispersion away from the emission source, creating vapour which may oxidise to form secondary organic aerosol. Air samples were collected from a street canyon, the adjacent park and an urban background site during the winter-spring period in central London, UK. Emissions of semi-volatile organic compounds (SVOCs) and intermediate volatility organic compounds (IVOCs) ranging from C to C in both the gas phase and particle phase were measured by using thermal desorption coupled to comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (TD-GC × GC-ToF-MS). Main compound groups identified and quantified were grouped alkanes (n-alkanes and branched alkanes), monocyclic alkanes, bicyclic alkanes and monocyclic aromatics. The carbon preference index (CPI) of n-alkanes was estimated to distinguish the emission sources. Pearson correlations between I/SVOCs and traffic tracers (black carbon, NO and benzene) in different locations were compared to analyse the influence of this emission source. The results indicate that while the major emission source at the roadside site is traffic, the lower correlations at background sites are indicative of other source contributions and/or differential reactivity of compounds. Gas-particle phase partitioning of n-alkanes is evaluated and compared between sites. The potential influence of gas phase I/SVOCs upon OH reactivity and secondary organic aerosol (SOA) formation is estimated and found to be relatively small.
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http://dx.doi.org/10.1016/j.scitotenv.2020.137470DOI Listing
June 2020

Long-term trends in PM mass and particle number concentrations in urban air: The impacts of mitigation measures and extreme events due to changing climates.

Environ Pollut 2020 Aug 2;263(Pt A):114500. Epub 2020 Apr 2.

International Laboratory for Air Quality and Health, Queensland University of Technology, Brisbane, Queensland, Australia. Electronic address:

Urbanisation and industrialisation led to the increase of ambient particulate matter (PM) concentration. While subsequent regulations may have resulted in the decrease of some PM matrices, the simultaneous changes in climate affecting local meteorological conditions could also have played a role. To gain an insight into this complex matter, this study investigated the long-term trends of two important matrices, the particle mass (PM) and particle number concentrations (PNC), and the factors that influenced the trends. Mann-Kendall test, Sen's slope estimator, the generalised additive model, seasonal decomposition of time series by LOESS (locally estimated scatterplot smoothing) and the Buishand range test were applied. Both PM and PNC showed significant negative monotonic trends (0.03-0.6 μg m. yr and 0.40-3.8 × 10 particles. cm. yr, respectively) except Brisbane (+0.1 μg m. yr and +53 particles. cm. yr, respectively). For the period covered in this study, temperature increased (0.03-0.07 °C.yr) in all cities except London; precipitation decreased (0.02-1.4 mm. yr) except in Helsinki; and wind speed was reduced in Brisbane and Rochester but increased in Helsinki, London and Augsburg. At the change-points, temperature increase in cold cities influenced PNC while shifts in precipitation and wind speed affected PM. Based on the LOESS trend, extreme events such as dust storms and wildfires resulting from changing climates caused a positive step-change in concentrations, particularly for PM. In contrast, among the mitigation measures, controlling sulphur in fuels caused a negative step-change, especially for PNC. Policies regarding traffic and fleet management (e.g. low emission zones) that were implemented only in certain areas or in a progressive uptake (e.g. Euro emission standards), resulted to gradual reductions in concentrations. Therefore, as this study has clearly shown that PM and PNC were influenced differently by the impacts of the changing climate and by the mitigation measures, both metrics must be considered in urban air quality management.
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http://dx.doi.org/10.1016/j.envpol.2020.114500DOI Listing
August 2020

Source apportionment of particle number size distribution in urban background and traffic stations in four European cities.

Environ Int 2020 02 4;135:105345. Epub 2019 Dec 4.

MRC-PHE Centre for Environment and Health, Environmental Research Group, King's College London, 150 Stamford Street, London SE1 9NH, UK.

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 NO 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 was blowing from the airport direction in all cities.
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http://dx.doi.org/10.1016/j.envint.2019.105345DOI Listing
February 2020

Surface ozone climatology of South Eastern Brazil and the impact of biomass burning events.

J Environ Manage 2019 Dec 11;252:109645. Epub 2019 Oct 11.

School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom.

In the austral spring, biomass fires affect a vast area of South America each year. We combined in situ ozone (O) data, measured in the states of São Paulo and Paraná, Brazil, in the period 2014-2017, with aerosol optical depth, co-pollutants (NOx, PM and PM) and air backtrajectories to identify sources, transport and geographical patterns in the air pollution data. We applied cluster analysis to hourly O data and split the investigation area of approximately 290,000 km into five groups with similar features in terms of diurnal, weekly, monthly and seasonal O concentrations. All groups presented a peak in September and October, associated with the fire activities and enhanced photochemistry. The highest mean O concentrations were measured inland whilst, besides having lower concentrations, the coastal group was also associated with the smallest diurnal and seasonal variations. The latter was attributed to lower photochemical activity due to frequently occurring overcast weather situation. The mean annual regional contribution of O over the area was 61 μg/m, with large seasonal and intersite variabilities (from 35 to 84 μg/m). The long-range transport of smoke contributed with between 23 and 41% of the total O during the pollution events. A pollution outbreak in September 2015 caused many-fold increases in O, PM and PM across the investigation area, which exceeded the World Health Organisation recommendations. We show that the regional transport of particulates and gas due to biomass burning overlays the local emissions in already highly polluted cities. Such an effect can outweigh local measures to curb anthropogenic air pollution in cities.
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http://dx.doi.org/10.1016/j.jenvman.2019.109645DOI Listing
December 2019

Characterization of Gas and Particulate Phase Organic Emissions (C-C) from a Diesel Engine and the Effect of Abatement Devices.

Environ Sci Technol 2019 Oct 10;53(19):11345-11352. Epub 2019 Sep 10.

Department of Environmental Sciences/Center of Excellence in Environmental Studies , King Abdulaziz University , P.O. Box 80203, Jeddah 21589 , Saudi Arabia.

Particulate and vapor phase emissions in the diluted exhaust of a light-duty diesel engine designed for Euro 5 application have been sampled. The engine was operated in three modes, and samples were collected from the exhaust without aftertreatment but also with aftertreatment by an exhaust oxidation catalyst and particle filter. The samples were analyzed by two-dimensional gas chromatography with time-of-flight mass spectral detection. The results show overall removal efficiencies for the organic compound mass by the combination of oxidation catalyst and particle filter of 50, 56, and 74% for the high-speed/high-load, low-speed/low-load, and high-speed/low-load conditions respectively. The results are clearly indicative of substantial repartitioning of the particulate and vapor components within the abatement devices and show an apparently reduced efficiency for the removal of high-molecular-weight alkanes under high-speed/high-load conditions relative to lower-molecular-weight compounds, although this may be due to alkane formation by thermocracking of other species. A notable feature is the presence of oxygenated compounds in the emissions, which are not present in the fuel. These are increased under high-speed/high-load conditions, and the results suggest the formation in the aftertreatment devices as well as in the combustion process.
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http://dx.doi.org/10.1021/acs.est.9b03053DOI Listing
October 2019

Ultrafine particles and PM in the air of cities around the world: Are they representative of each other?

Environ Int 2019 08 21;129:118-135. Epub 2019 May 21.

Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, CA 90089, USA.

Can mitigating only particle mass, as the existing air quality measures do, ultimately lead to reduction in ultrafine particles (UFP)? The aim of this study was to provide a broader urban perspective on the relationship between UFP, measured in terms of particle number concentration (PNC) and PM (mass concentration of particles with aerodynamic diameter < 2.5 μm) and factors that influence their concentrations. Hourly average PNC and PM were acquired from 10 cities located in North America, Europe, Asia, and Australia over a 12-month period. A pairwise comparison of the mean difference and the Kolmogorov-Smirnov test with the application of bootstrapping were performed for each city. Diurnal and seasonal trends were obtained using a generalized additive model (GAM). The particle number to mass concentration ratios and the Pearson's correlation coefficient were calculated to elucidate the nature of the relationship between these two metrics. Results show that the annual mean concentrations ranged from 8.0 × 10 to 19.5 × 10 particles·cm and from 7.0 to 65.8 μg·m for PNC and PM, respectively, with the data distributions generally skewed to the right, and with a wider spread for PNC. PNC showed a more distinct diurnal trend compared with PM, attributed to the high contributions of UFP from vehicular emissions to PNC. The variation in both PNC and PM due to seasonality is linked to the cities' geographical location and features. Clustering the cities based on annual median concentrations of both PNC and PM demonstrated that a high PNC level does not lead to a high PM, and vice versa. The particle number-to-mass ratio (in units of 10 particles·μg) ranged from 0.14 to 2.2, >1 for roadside sites and <1 for urban background sites with lower values for more polluted cities. The Pearson's r ranged from 0.09 to 0.64 for the log-transformed data, indicating generally poor linear correlation between PNC and PM. Therefore, PNC and PM measurements are not representative of each other; and regulating PM does little to reduce PNC. This highlights the need to establish regulatory approaches and control measures to address the impacts of elevated UFP concentrations, especially in urban areas, considering their potential health risks.
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http://dx.doi.org/10.1016/j.envint.2019.05.021DOI Listing
August 2019

Diesel exhaust nanoparticles and their behaviour in the atmosphere.

Proc Math Phys Eng Sci 2018 Dec 19;474(2220):20180492. Epub 2018 Dec 19.

School of Geography, Earth and Environmental Sciences, School of Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.

Diesel engine emissions are by far the largest source of nanoparticles in many urban atmospheres, in which they dominate the particle number count, and may present a significant threat to public health. This paper reviews knowledge of the composition and atmospheric properties of diesel exhaust particles, and exemplifies research in this field through a description of the FASTER project (Fundamental Studies of the Sources, Properties and Environmental Behaviour of Exhaust Nanoparticles from Road Vehicles) which studied the size distribution-and, in unprecedented detail, the chemical composition-of nanoparticles sampled from diesel engine exhaust. This information has been systematized and used to inform the development of computational modules that simulate the behaviour of the largely semi-volatile content of the nucleation mode particles, including consequent effects on the particle size distribution, under typical atmospheric conditions. Large-eddy model studies have informed a simpler characterization of flow around the urban built environment, and include aerosol processes. This modelling and engine-laboratory work have been complemented by laboratory measurements of vapour pressures, and the execution of two field measurement campaigns in London. The result is a more robust description of the dynamical behaviour on the sub-kilometre scale of diesel exhaust nanoparticles and their importance as an urban air pollutant.
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http://dx.doi.org/10.1098/rspa.2018.0492DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6304020PMC
December 2018

Comparison of Machine Learning Approaches with a General Linear Model To Predict Personal Exposure to Benzene.

Environ Sci Technol 2018 10 14;52(19):11215-11222. Epub 2018 Sep 14.

Division of Environmental Health and Risk Management School of Geography, Earth and Environmental Sciences , University of Birmingham , Edgbaston, Birmingham , B15 2TT , United Kingdom.

Machine learning techniques (MLTs) offer great power in analyzing complex data sets and have not previously been applied to non-occupational pollutant exposure. MLT models that can predict personal exposure to benzene have been developed and compared with a standard model using a linear regression approach (GLM). The models were tested against independent data sets obtained from three personal exposure measurement campaigns. A correlation-based feature subset (CFS) selection algorithm identified a reduced attribute set, with common attributes grouped under the use of paints in homes, upholstery materials, space heating, and environmental tobacco smoke as the attributes suitable to predict the personal exposure to benzene. Personal exposure was categorized as low, medium, and high, and for big data sets, both the GLM and MLTs show high variability in performance to correctly classify greater than 90 percentile concentrations, but the MLT models have a higher score when accounting for divergence of incorrectly classified cases. Overall, the MLTs perform at least as well as the GLM and avoid the need to input microenvironment concentrations.
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http://dx.doi.org/10.1021/acs.est.8b03328DOI Listing
October 2018

Regions of open water and melting sea ice drive new particle formation in North East Greenland.

Sci Rep 2018 04 17;8(1):6109. Epub 2018 Apr 17.

Arctic Research Centre, Department of Environmental Science, Aarhus University, 4000, Roskilde, Denmark.

Atmospheric new particle formation (NPF) and growth significantly influences the indirect aerosol-cloud effect within the polar climate system. In this work, the aerosol population is categorised via cluster analysis of aerosol number size distributions (9-915 nm, 65 bins) taken at Villum Research Station, Station Nord (VRS) in North Greenland during a 7 year record (2010-2016). Data are clustered at daily averaged resolution; in total, we classified six categories, five of which clearly describe the ultrafine aerosol population, one of which is linked to nucleation events (up to 39% during summer). Air mass trajectory analyses tie these frequent nucleation events to biogenic precursors released by open water and melting sea ice regions. NPF events in the studied regions seem not to be related to bird colonies from coastal zones. Our results show a negative correlation (r = -0.89) between NPF events and sea ice extent, suggesting the impact of ultrafine Arctic aerosols is likely to increase in the future, given the likely increased sea ice melting. Understanding the composition and the sources of Arctic aerosols requires further integrated studies with joint multi-component ocean-atmosphere observation and modelling.
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http://dx.doi.org/10.1038/s41598-018-24426-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5904185PMC
April 2018

Modelling traffic-induced multicomponent ultrafine particles in urban street canyon compartments: Factors that inhibit mixing.

Environ Pollut 2018 Jul 20;238:186-195. Epub 2018 Mar 20.

School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK; Department of Environmental Sciences/Center of Excellence in Environmental Studies, King Abdulaziz University, PO Box 80203, Jeddah, 21589, Saudi Arabia.

This study implements a two-box model coupled with ultrafine particle (UFP) multicomponent microphysics for a compartmentalised street canyon. Canyon compartmentalisation can be described parsimoniously by three parameters relating to the features of the canyon and the atmospheric state outside the canyon, i.e. the heterogeneity coefficient, the vortex-to-vortex exchange velocity, and the box height ratio. The quasi-steady solutions for the two compartments represent a balance among emissions, microphysical aerosol dynamics (i.e. evaporation/condensation of semi-volatiles, SVOCs), and exchange processes, none of which is negligible. This coupled two-box model can capture significant contrasts in UFP number concentrations and a measure of the volatility of the multi-SVOC-particles in the lower and upper canyon. Modelled ground-level UFP number concentrations vary across nucleation, Aitken, and accumulation particle modes as well-defined monotonic functions of canyon compartmentalisation parameters. Compared with the two-box model, a classic one-box model (without canyon compartmentalisation) leads to underestimation of UFP number concentrations by several tens of percent typically. By quantifying the effects of canyon compartmentalisation, this study provides a framework for understanding how canyon geometry and the presence of street trees, street furniture, and architectural features interact with the large-scale atmospheric flow to determine ground-level pollutant concentrations.
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http://dx.doi.org/10.1016/j.envpol.2018.03.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5971220PMC
July 2018

Novel insights on new particle formation derived from a pan-european observing system.

Sci Rep 2018 01 24;8(1):1482. Epub 2018 Jan 24.

National Centre for Atmospheric Science Division of Environmental Health & Risk Management School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom.

The formation of new atmospheric particles involves an initial step forming stable clusters less than a nanometre in size (<~1 nm), followed by growth into quasi-stable aerosol particles a few nanometres (~1-10 nm) and larger (>~10 nm). Although at times, the same species can be responsible for both processes, it is thought that more generally each step comprises differing chemical contributors. Here, we present a novel analysis of measurements from a unique multi-station ground-based observing system which reveals new insights into continental-scale patterns associated with new particle formation. Statistical cluster analysis of this unique 2-year multi-station dataset comprising size distribution and chemical composition reveals that across Europe, there are different major seasonal trends depending on geographical location, concomitant with diversity in nucleating species while it seems that the growth phase is dominated by organic aerosol formation. The diversity and seasonality of these events requires an advanced observing system to elucidate the key processes and species driving particle formation, along with detecting continental scale changes in aerosol formation into the future.
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http://dx.doi.org/10.1038/s41598-017-17343-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5784154PMC
January 2018

Vertical variation of PM mass and chemical composition, particle size distribution, NO, and BTEX at a high rise building.

Environ Pollut 2018 Apr 4;235:339-349. Epub 2018 Jan 4.

Division of Environmental Health and Risk Management, School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom.

Substantial efforts have been made in recent years to investigate the horizontal variability of air pollutants at regional and urban scales and epidemiological studies have taken advantage of resulting improvements in exposure assessment. On the contrary, only a few studies have investigated the vertical variability and their results are not consistent. In this study, a field experiment has been conducted to evaluate the variation of concentrations of different particle metrics and gaseous pollutants on the basis of floor height at a high rise building. Two 15-day monitoring campaigns were conducted in the urban area of Bologna, Northern Italy, one of the most polluted areas in Europe. Measurements sites were operated simultaneously at 2, 15, 26, 44 and 65 m a.g.l. Several particulate matter metrics including PM mass and chemical composition, particle number concentration and size distribution were measured. Time integrated measurement of NO and BTEX were also included in the monitoring campaigns. Measurements showed relevant vertical gradients for most traffic related pollutants. A monotonic gradient of PM was found with ground-to-top differences of 4% during the warm period and 11% during the cold period. Larger gradients were found for UFP (∼30% during both seasons) with a substantial loss of particles from ground to top in the sub-50 nm size range. The largest drops in concentrations for chemical components were found for Elemental Carbon (-27%), iron (-11%) and tin (-36%) during winter. The ground-to-top decline of concentrations for NO and benzene during winter was equal to 74% and 35%, respectively. In conclusion, our findings emphasize the need to include vertical variations of urban air pollutants when evaluating population exposure and associated health effects, especially in relation to some traffic related pollutants and particle metrics.
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http://dx.doi.org/10.1016/j.envpol.2017.12.090DOI Listing
April 2018

Antarctic sea ice region as a source of biogenic organic nitrogen in aerosols.

Sci Rep 2017 07 20;7(1):6047. Epub 2017 Jul 20.

Institut de Ciències del Mar, CSIC, Pg. Marítim de la Barceloneta 37-49, 08003, Barcelona, Catalonia, Spain.

Climate warming affects the development and distribution of sea ice, but at present the evidence of polar ecosystem feedbacks on climate through changes in the atmosphere is sparse. By means of synergistic atmospheric and oceanic measurements in the Southern Ocean near Antarctica, we present evidence that the microbiota of sea ice and sea ice-influenced ocean are a previously unknown significant source of atmospheric organic nitrogen, including low molecular weight alkyl-amines. Given the keystone role of nitrogen compounds in aerosol formation, growth and neutralization, our findings call for greater chemical and source diversity in the modelling efforts linking the marine ecosystem to aerosol-mediated climate effects in the Southern Ocean.
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http://dx.doi.org/10.1038/s41598-017-06188-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5519629PMC
July 2017

Arctic sea ice melt leads to atmospheric new particle formation.

Sci Rep 2017 06 12;7(1):3318. Epub 2017 Jun 12.

Centre for Atmospheric Science Division of Environmental Health & Risk Management School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom.

Atmospheric new particle formation (NPF) and growth significantly influences climate by supplying new seeds for cloud condensation and brightness. Currently, there is a lack of understanding of whether and how marine biota emissions affect aerosol-cloud-climate interactions in the Arctic. Here, the aerosol population was categorised via cluster analysis of aerosol size distributions taken at Mt Zeppelin (Svalbard) during a 11 year record. The daily temporal occurrence of NPF events likely caused by nucleation in the polar marine boundary layer was quantified annually as 18%, with a peak of 51% during summer months. Air mass trajectory analysis and atmospheric nitrogen and sulphur tracers link these frequent nucleation events to biogenic precursors released by open water and melting sea ice regions. The occurrence of such events across a full decade was anti-correlated with sea ice extent. New particles originating from open water and open pack ice increased the cloud condensation nuclei concentration background by at least ca. 20%, supporting a marine biosphere-climate link through sea ice melt and low altitude clouds that may have contributed to accelerate Arctic warming. Our results prompt a better representation of biogenic aerosol sources in Arctic climate models.
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http://dx.doi.org/10.1038/s41598-017-03328-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5468288PMC
June 2017

Efficacy of Recent Emissions Controls on Road Vehicles in Europe and Implications for Public Health.

Sci Rep 2017 04 25;7(1):1152. Epub 2017 Apr 25.

School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.

Road traffic is a major source of urban air pollution responsible for substantial premature mortality. Until recently, attention has focussed primarily on exhaust emissions of particulate matter from traffic as a causal factor. From analysis of air quality measurement data from the UK and France, we demonstrate that road traffic exhaust has a far greater impact on concentrations of nitrogen dioxide than of PM. PM and carbonaceous particle concentrations have been declining appreciably since 2010/11 due to the use of diesel particle filters, but little change is seen in nitrogen dioxide over the period from 1995 to 2015. It is shown that the effect of NO from road traffic upon premature mortality was ten-fold greater than that of PM even before the widespread use of diesel particle filters, and is now considerably larger. The overwhelming contribution of diesel compared to gasoline-fuelled vehicles to emissions of both PM and NO emphasises the importance of further controls on emissions from diesels.
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http://dx.doi.org/10.1038/s41598-017-01135-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5430659PMC
April 2017