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Air ions are electrically charged particles in air. They are ubiquitous in the natural environment and affect the Earth's radiation budget by accelerating the formation and growth of new aerosol particles. Despite this, few datasets exist exploring these effects in the urban environment. A neutral cluster and air ion spectrometer was deployed in Leipzig, Germany, to measure the number size distribution of charged particles from 0.8 to 42 nm, between 27 July and 25 August 2022. Following previous analyses, charged particles were classified into small (0.8–1.6 nm), intermediate (1.6–7.5 nm), and large (7.5–22 nm) fractions by mass diameter, and their mean concentrations (sum of positive and negative polarities) during the campaign were 405, 71.6, and 415 cm -3 , respectively. The largest peaks in intermediate and large ions were explained by new particle formation (NPF), with intermediate ions correlating well with sulfuric acid dimer. Smaller morning and evening peaks were coincident with black carbon concentrations and attributed to primary emissions. NPF events, observed on 30 % of days, coincided with intense solar radiation and elevated sulfuric acid dimer. Small charged particles were primarily associated with radioactive decay and highest during the early hours, and they are unrelated to primary emissions or NPF. The apparent contributions of charged particles to 3 and 7.5 nm particle formation rates were 5.7 % and 12.7 %, respectively, with mean growth rates of 4.0 nm h -1 between 3–7.5 nm and 5.2 nm h -1 between 7.5 and 22 nm. The ratio of charged to total particle formation rates at 3 nm suggests a minor role for charged particles in NPF. We conclude that NPF is a primary source of > 3 nm ions in our data, with primary emissions being the major source in the absence of NPF. [ABSTRACT FROM AUTHOR]

Lockdown restrictions in response to the COVID-19 pandemic led to the curtailment of many activities and reduced emissions of primary air pollutants. Here, we applied positive matrix factorisation to particle size distribution (PSD) data from six monitoring sites (three urban background and three roadside) between four European cities (Helsinki, Leipzig, Budapest, and London) to evaluate how particle number concentrations (PNCs) and their sources changed during the respective 2020 lockdown periods compared to the reference years 2014–2019. A number of common factors were resolved between sites, including nucleation, road traffic semi-volatile fraction (road traffic svf), road traffic solid fraction (road traffic sf), diffuse urban (wood smoke + aged traffic), ozone-associated secondary aerosol (O 3 -associated SA), and secondary inorganic aerosol (SIA). Nucleation, road traffic, and diffuse urban factors were the largest contributors to mean PNCs during the reference years and respective lockdown periods. However, SIA factors were the largest contributors to particle mass concentrations, irrespective of environment type. Total mean PNCs were lower at two of the urban-background and all roadside sites during lockdown. The response of nucleation and road traffic svf factors to lockdown restrictions was highly variable, although road traffic sf factors were consistently lower at roadside sites. The responses of diffuse urban factors were largely consistent and were mostly lower at urban-background sites. Secondary aerosols (O 3 -associated SA and SIA) exhibited extensive reductions in their mean PNCs at all sites. These variegated responses to lockdowns across Europe point to a complex network of sources and aerosol sinks contributing to PSDs. [ABSTRACT FROM AUTHOR]

Antarctica and the Southern Ocean (SO) are the most pristine areas of the globe and represent ideal places to investigate aerosol–climate interactions in an unperturbed atmosphere. In this study, we present submicrometer aerosol (PM 1) source apportionment for two sample sets collected in parallel at the British Antarctic Survey stations of Signy and Halley during the austral summer of 2018–2019. Water-soluble organic matter (WSOM) is a major aerosol component at both sites (37 % and 29 % of water-soluble PM 1 , on average, at Signy and Halley, respectively). Remarkable differences between pelagic (open-ocean) and sympagic (influenced by sea ice) air mass histories and related aerosol sources are found. The application of factor analysis techniques to series of spectra obtained by means of proton-nuclear magnetic resonance (H-NMR) spectroscopy on the samples allows the identification of five organic aerosol (OA) sources: two primary organic aerosol (POA) types, characterized by sugars, polyols, and degradation products of lipids and associated with open-ocean and sympagic/coastal waters, respectively; two secondary organic aerosol (SOA) types, one enriched in methanesulfonic acid (MSA) and dimethylamine (DMA) and associated with pelagic waters and the other characterized by trimethylamine (TMA) and linked to sympagic environments; and a fifth component of unclear origin, possibly associated with the atmospheric aging of primary emissions. Overall, our results strongly indicate that the emissions from sympagic and pelagic ecosystems affect the variability in the submicrometer aerosol composition in the study area, with atmospheric circulation establishing marked latitudinal gradients only for some of the aerosol components (e.g., the sympagic components) while distributing the others (e.g., pelagic and/or aged components) both in maritime and inner Antarctic regions. [ABSTRACT FROM AUTHOR]

In order to reduce the uncertainty of aerosol radiative forcing in global climate models, we need to better understand natural aerosol sources which are important to constrain the current and pre-industrial climate. Here, we analyze Particle Number Size Distributions (PNSD) collected during a year (2015) across four coastal and inland Antarctic research bases (Halley, Marambio, Concordia/Dome C and King Sejong). We find that the four Antarctic locations have striking differences in PNSD, stressing multiple aerosol sources and processes likely exist. We utilise k-means cluster analysis to separate the PNSD data into six main categories. Nucleation and Bursting PNSDs occur 28-48% of the time between sites, most commonly at coastal sites Marambio and King Sejong where air masses mostly come from the west and travel over extensive regions of sea ice, marginal ice, and open ocean, and likely arise from new particle formation. Aitken high, Aitken low, and bimodal PNSDs occur 37-68% of the time, most commonly at Concordia/Dome C on the Antarctic Plateau, and likely arise from atmospheric transport and aging from aerosol originating likely in both coastal boundary layer and free troposphere. Pristine PNSDs with low aerosol concentrations occur 12-45% of the time, most common at Halley located at low altitudes and far from the coastal melting ice, and influenced by air masses from the west. The Antarctic Atmospheric circulation has a strong control on the air mass origin type. Most of the time Marambio and King Sejong stations are affected by Easterly air masses, whereas Halley gets air masses mainly from the Weddell sea marginal and consolidated pack ice. Not only the sea spray primary aerosols and gas to particle secondary aerosols sources, but also the different air masses impacting the research stations should be kept in mind when deliberating upon different aerosol precursors sources across research stations. We provide evidence that both primary and secondary components from pelagic and sympagic regions strongly contribute to the annual seasonal cycle of Antarctic aerosols which add insight on the possible sources of aerosol production/activity in the whole Antarctic region. Our simultaneous aerosol measurements stress the importance of the variation in atmospheric biogeochemistry across the Antarctic region. [ABSTRACT FROM AUTHOR]

Antarctica and the Southern Ocean are the most pristine areas of the globe and represent ideal places to investigate aerosol-climate interactions in an unperturbed atmosphere. In this study, we present PM1 (Particulate Matter < 1µm) source apportionment for two sample sets collected in parallel at two British Antarctic Survey (BAS) stations, namely Signy and Halley, during the austral summer 2018–2019. We find that Water Soluble Organic Matter (WSOM) is a major aerosol component at both sites (average 25–33 %). Remarkable differences between pelagic (open ocean) and sympagic (influenced by sea ice) air mass histories and related aerosol sources are found. The application of non-negative factor analysis techniques to H-NMR spectra of the samples allows the identification of five Organic Aerosol (OA) sources: two primary (POA) types, two secondary (SOA) types, and a fifth component of unclear origin possibly associated with the atmospheric ageing of primary emissions and dominating at Halley. Overall, the concentrations of primary and secondary organic aerosols are prevalently dictated by the emissions in sympagic and pelagic marine regions, with atmospheric circulation causing to establish marked latitudinal gradients only for some of such aerosol components. Our results strongly indicate that various sources and aerosols processes are controlling the Antarctic aerosol population, with the emissions from sympagic and pelagic ecosystems affecting the variability of submicron aerosol composition both in maritime areas as in inner Antarctic regions. [ABSTRACT FROM AUTHOR]

The Arctic is a rapidly changing ecosystem, with complex ice–ocean–atmosphere feedbacks. An important process is new particle formation (NPF), from gas-phase precursors, which provides a climate forcing effect. NPF has been studied comprehensively at different sites in the Arctic, ranging from those in the High Arctic and those at Svalbard to those in the continental Arctic, but no harmonised analysis has been performed on all sites simultaneously, with no calculations of key NPF parameters available for some sites. Here, we analyse the formation and growth of new particles from six long-term ground-based stations in the Arctic (Alert, Villum, Tiksi, Zeppelin Mountain, Gruvebadet, and Utqiaġvik). Our analysis of particle formation and growth rates in addition to back-trajectory analysis shows a summertime maxima in the frequency of NPF and particle formation rate at all sites, although the mean frequency and particle formation rates themselves vary greatly between sites, with the highest at Svalbard and lowest in the High Arctic. The summertime growth rate, condensational sinks, and vapour source rates show a slight bias towards the southernmost sites, with vapour source rates varying by around an order of magnitude between the northernmost and southernmost sites. Air masses back-trajectories during NPF at these northernmost sites are associated with large areas of sea ice and snow, whereas events at Svalbard are associated with more sea ice and ocean regions. Events at the southernmost sites are associated with large areas of land and sea ice. These results emphasise how understanding the geographical variation in surface type across the Arctic is key to understanding secondary aerosol sources and providing a harmonised analysis of NPF across the Arctic. [ABSTRACT FROM AUTHOR]

The Arctic environment is rapidly changing due to accelerated warming in the region. The warming trend is driving a decline in sea ice extent, which thereby enhances feedback loops in the surface energy budget in the Arctic. Arctic aerosols play an important role in the radiative balance and hence the climate response in the region, yet direct observations of aerosols over the Arctic Ocean are limited. In this study, we investigate the annual cycle in the aerosol particle number size distribution (PNSD), particle number concentration (PNC), and black carbon (BC) mass concentration in the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. This is the first continuous, year-long data set of aerosol PNSD ever collected over the sea ice in the central Arctic Ocean. We use a k -means cluster analysis, FLEXPART simulations, and inverse modeling to evaluate seasonal patterns and the influence of different source regions on the Arctic aerosol population. Furthermore, we compare the aerosol observations to land-based sites across the Arctic, using both long-term measurements and observations during the year of the MOSAiC expedition (2019–2020), to investigate interannual variability and to give context to the aerosol characteristics from within the central Arctic. Our analysis identifies that, overall, the central Arctic exhibits typical seasonal patterns of aerosols, including anthropogenic influence from Arctic haze in winter and secondary aerosol processes in summer. The seasonal pattern corresponds to the global radiation, surface air temperature, and timing of sea ice melting/freezing, which drive changes in transport patterns and secondary aerosol processes. In winter, the Norilsk region in Russia/Siberia was the dominant source of Arctic haze signals in the PNSD and BC observations, which contributed to higher accumulation-mode PNC and BC mass concentrations in the central Arctic than at land-based observatories. We also show that the wintertime Arctic Oscillation (AO) phenomenon, which was reported to achieve a record-breaking positive phase during January–March 2020, explains the unusual timing and magnitude of Arctic haze across the Arctic region compared to longer-term observations. In summer, the aerosol PNCs of the nucleation and Aitken modes are enhanced; however, concentrations were notably lower in the central Arctic over the ice pack than at land-based sites further south. The analysis presented herein provides a current snapshot of Arctic aerosol processes in an environment that is characterized by rapid changes, which will be crucial for improving climate model predictions, understanding linkages between different environmental processes, and investigating the impacts of climate change in future Arctic aerosol studies. [ABSTRACT FROM AUTHOR]

Knowledge of air pollution sources is important in policymaking and air pollution mitigation. Until recently, source apportion analyses were limited and only possible with the use of expensive regulatory-grade instruments. In the present study we applied a two-step positive matrix factorisation (PMF) receptor analysis at a background site in Birmingham, UK using data acquired by low-cost sensors (LCSs). The application of PMF allowed for the identification of the sources that affect the local air quality, clearly separating different sources of particulate matter (PM) pollution. Furthermore, the method allowed for the contribution of different air pollution sources to the overall air quality at the site to be estimated, thereby providing pollution source apportionment. The use of data from regulatory-grade (RG) instruments further confirmed the reliability of the results, as well as further clarifying the particulate matter composition and origin. Compared with the results from a previous analysis, in which a k -means clustering algorithm was used, a good consistency between the k means and PMF results was found in pinpointing and separating the sources of pollution that affect the site. The potential and limitations of each method when used with low-cost sensor data are highlighted. The analysis presented in this study paves the way for more extensive use of LCSs for atmospheric applications, receptor modelling and source apportionment. Here, we present the infrastructure for understanding the factors that affect air quality at a significantly lower cost than previously possible. This should provide new opportunities for regulatory and indicative monitoring for both scientific and industrial applications. [ABSTRACT FROM AUTHOR]

The Arctic environment is rapidly changing due to accelerated warming in the region. The warming trend is driving a decline in sea ice extent, which thereby enhances feedback loops in the surface energy budget in the Arctic. Arctic aerosols play an important role in the radiative balance, and hence the climate response, in the region; yet direct observations of aerosols over the Arctic Ocean are limited. In this study, we investigate the annual cycle in the aerosol particle number size distribution (PNSD), particle number concentration (PNC), and black carbon (BC) mass concentration in the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. This is the first continuous, year-long dataset of aerosol PNSD ever collected over the sea ice in the central Arctic Ocean. We use a k-means cluster analysis, FLEXPART simulations, and inverse modeling to evaluate seasonal patterns and the influence of different source regions on the Arctic aerosol population. Furthermore, we compare the aerosol observations to land-based sites across the Arctic, using both long-term measurements and observations during the year of the MOSAiC expedition (2019 - 2020), to investigate interannual variability and to give context to the aerosol characteristics from within the central Arctic. Our analysis identifies that, overall, the central Arctic exhibits typical seasonal patterns of aerosols, including anthropogenic influence from Arctic Haze in winter and secondary aerosol processes in summer. The seasonal pattern corresponds with the global radiation, surface air temperature, and the timing of sea ice melting/freezing, which drives changes in transport patterns and secondary aerosol processes. In winter, the Norilsk region in Russia/Siberia was the dominant source of Arctic Haze signal in the PNSD and BC observations, which contributed to higher accumulation mode PNC and BC mass concentration in the central Arctic than at land-based observatories. We also show that the wintertime Arctic Oscillation (AO) phenomenon, which was reported to achieve a record-breaking positive phase during January - March 2020, explains the unusual timing and magnitude of Arctic Haze across the Arctic region compared to longer-term observations. In summer, the PNC of nucleation and Aitken mode aerosol is enhanced, but concentrations were notably lower in the central Arctic over the ice pack than at land-based sites further south. The analysis presented herein provides a current snapshot of Arctic aerosol processes in an environment that is characterized by rapid changes, which will be crucial for improving climate model predictions, understanding linkages between different environmental processes, and investigating the impacts of climate change in future Arctic aerosol studies. [ABSTRACT FROM AUTHOR]

The Arctic is a rapidly changing ecosystem, with complex ice-ocean-atmosphere feedbacks. An important process new particle formation (NPF) from gas phase precursors, which provide a climate forcing effect. NPF has been studied comprehensively at different sites in the Arctic ranging from those in the high Arctic, those at Svalbard, and those in the continental Arctic, but no harmonized analysis has been performed on all sites simultaneously, with no calculations of key NPF parameters available for some sites. Here, we analyse the formation and growth of new particles from six long-term ground-based stations in the Arctic (Alert, Villum, Tiksi, Mt. Zeppelin, Gruvebadet. & Utqiagvik). Our analysis of particle formation and growth rates, as well as back trajectory analysis shows summertime maxima in frequency of NPF and particle formation rate at all sites, although the mean frequency and particle formation rates themselves vary greatly between sites, highest at Svalbard, and lowest in the high Arctic. Growth rate, condensational sinks and vapour source rates show a slight bias towards the southernmost sites, with vapour source rates varying by around an order of magnitude between the northernmost and southernmost sites. Air masse back trajectories during NPF at these northernmost sites are associated with large areas of sea ice and snow, whereas events at Svalbard are associated with more sea ice and ocean regions. Events at the southernmost sites are associated with large areas of land, and sea ice. These results emphasize how understanding the geographical variation in surface type across the Arctic is key to understanding secondary aerosol sources, and provide harmonised analysis of NPF across the Arctic. [ABSTRACT FROM AUTHOR]

Delhi is one of the world's most polluted cities, with very high concentrations of airborne particulate matter. However, little is known about the factors controlling the characteristics of wide-range particle number size distributions. Here, new measurements are reported from three field campaigns conducted in winter and pre-monsoon and post-monsoon seasons at the Indian Institute of Technology campus in the south of the city. Particle number size distributions were measured simultaneously, using a scanning mobility particle sizer and a GRIMM optical particle monitor, covering 15 nm to >10 µm diameter. The merged, wide-range size distributions were categorized into the following five size ranges: nucleation (15–20 nm), Aitken (20–100 nm), accumulation (100 nm–1 µm), large fine (1–2.5 µm), and coarse (2.5–10 µm) particles. The ultrafine fraction (15–100 nm) accounts for about 52 % of all particles by number (PN 10 is the total particle number from 15 nm to 10 µm) but just 1 % by PM 10 volume (PV 10 is the total particle volume from 15 nm to 10 µm). The measured size distributions are markedly coarser than most from other parts of the world but are consistent with earlier cascade impactor data from Delhi. Our results suggest substantial aerosol processing by coagulation, condensation, and water uptake in the heavily polluted atmosphere, which takes place mostly at nighttime and in the morning hours. Total number concentrations are highest in winter, but the mode of the distribution is largest in the post-monsoon (autumn) season. The accumulation mode particles dominate the particle volume in autumn and winter, while the coarse mode dominates in summer. Polar plots show a huge variation between both size fractions in the same season and between seasons for the same size fraction. The diurnal pattern of particle numbers is strongly reflective of a road traffic influence upon concentrations, especially in autumn and winter, although other sources, such as cooking and domestic heating, may influence the evening peak. There is a clear influence of diesel traffic at nighttime, when it is permitted to enter the city, and also indications in the size distribution data of a mode < 15 nm, which is probably attributable to CNG/LPG vehicles. New particle formation appears to be infrequent and is, in this dataset, limited to 1 d in the summer campaign. Our results reveal that the very high emissions of airborne particles in Delhi, particularly from traffic, determine the variation in particle number size distributions. [ABSTRACT FROM AUTHOR]

Delhi is one of the world's most polluted cities, with very high concentrations of airborne particulate matter. However, little is known on the factors controlling the characteristics of particle number size distributions. Here, new measurements are reported from three field campaigns conducted in winter, pre-monsoon and post-monsoon seasons on the Indian Insitute of Technology campus in the south of the city. Particle number size distributions were measured simultaneously using a Scanning Mobility Particle Sizer and a Grimm optical particle monitor, covering 15 nm to >10 µm diameter. The merged, wide-range size distributions were categorised into five size ranges: nucleation (15-20 nm), Aitken (20-100 nm), accumulation (100 nm-1 µm), large fine (1-2.5 µm) and coarse (2.5-10 µm) particles. The ultrafine fraction (15-100 nm) accounts for about 52 % of all particles by number (PN10), but just 1 % by PM10 volume (PV10). The measured size distributions are markedly coarser than most from other parts of the world, but are consistent with earlier cascade impactor data from Delhi. Our results suggest substantial aerosol processing by coagulation, condensation and water uptake in the heavily polluted atmosphere, which takes place mostly at nighttime and in the morning hours. Total number concentrations are highest in winter, but the mode of the distribution is largest in the post-monsoon (autumn) season. The accumulation mode particles dominate the particle volume in autumn and winter, while the coarse mode dominates in summer. Polar plots show a huge variation between both size fractions in the same season and between seasons for the same size fraction. The diurnal pattern of particle numbers is strongly reflective of a road traffic influence upon concentrations, especially in autumn and winter. There is a clear influence of diesel traffic at nighttime when it is permitted to enter the city, and also indications in the size distribution data of a mode <15 nm, probably attributable to CNG/LPG vehicles. New particle formation appears to be infrequent, and in this dataset is limited to one day in the summer campaign. Our results reveal that the very high emissions of airborne particles in Delhi, particularly from traffic, determine the variation of particle number size distributions. [ABSTRACT FROM AUTHOR]

The Indian megacity of Delhi suffers from some of the poorest air quality in the world. While ambient NO 2 and particulate matter (PM) concentrations have received considerable attention in the city, high ground-level ozone (O 3) concentrations are an often overlooked component of pollution. O 3 can lead to significant ecosystem damage and agricultural crop losses, and adversely affect human health. During October 2018, concentrations of speciated non-methane hydrocarbon volatile organic compounds (C 2 –C 13), oxygenated volatile organic compounds (o-VOCs), NO, NO 2 , HONO, CO, SO 2 , O 3 , and photolysis rates, were continuously measured at an urban site in Old Delhi. These observations were used to constrain a detailed chemical box model utilising the Master Chemical Mechanism v3.3.1. VOCs and NO x (NO + NO 2) were varied in the model to test their impact on local O 3 production rates, P(O3) , which revealed a VOC-limited chemical regime. When only NO x concentrations were reduced, a significant increase in P(O3) was observed; thus, VOC co-reduction approaches must also be considered in pollution abatement strategies. Of the VOCs examined in this work, mean morning P(O3) rates were most sensitive to monoaromatic compounds, followed by monoterpenes and alkenes, where halving their concentrations in the model led to a 15.6 %, 13.1 %, and 12.9 % reduction in P(O3) , respectively. P(O3) was not sensitive to direct changes in aerosol surface area but was very sensitive to changes in photolysis rates, which may be influenced by future changes in PM concentrations. VOC and NO x concentrations were divided into emission source sectors, as described by the Emissions Database for Global Atmospheric Research (EDGAR) v5.0 Global Air Pollutant Emissions and EDGAR v4.3.2_VOC_spec inventories, allowing for the impact of individual emission sources on P(O3) to be investigated. Reducing road transport emissions only, a common strategy in air pollution abatement strategies worldwide, was found to increase P(O3) , even when the source was removed in its entirety. Effective reduction in P(O3) was achieved by reducing road transport along with emissions from combustion for manufacturing and process emissions. Modelled P(O3) reduced by ∼ 20 ppb h -1 when these combined sources were halved. This study highlights the importance of reducing VOCs in parallel with NO x and PM in future pollution abatement strategies in Delhi. [ABSTRACT FROM AUTHOR]

New particle formation (NPF) events occur almost everywhere in the world and can play an important role as a particle source. The frequency and characteristics of NPF events vary spatially, and this variability is yet to be fully understood. In the present study, long-term particle size distribution datasets (minimum of 3 years) from 13 sites of various land uses and climates from across Europe were studied, and NPF events, deriving from secondary formation and not traffic-related nucleation, were extracted and analysed. The frequency of NPF events was consistently found to be higher at rural background sites, while the growth and formation rates of newly formed particles were higher at roadsides (though in many cases differences between the sites were small), underlining the importance of the abundance of condensable compounds of anthropogenic origin found there. The growth rate was higher in summer at all rural background sites studied. The urban background sites presented the highest uncertainty due to greater variability compared to the other two types of site. The origin of incoming air masses and the specific conditions associated with them greatly affect the characteristics of NPF events. In general, cleaner air masses present higher probability for NPF events, while the more polluted ones show higher growth rates. However, different patterns of NPF events were found, even at sites in close proximity (< 200 km), due to the different local conditions at each site. Region-wide events were also studied and were found to be associated with the same conditions as local events, although some variability was found which was associated with the different seasonality of the events at two neighbouring sites. NPF events were responsible for an increase in the number concentration of ultrafine particles of more than 400 % at rural background sites on the day of their occurrence. The degree of enhancement was less at urban sites due to the increased contribution of other sources within the urban environment. It is evident that, while some variables (such as solar radiation intensity, relative humidity, or the concentrations of specific pollutants) appear to have a similar influence on NPF events across all sites, it is impossible to predict the characteristics of NPF events at a site using just these variables, due to the crucial role of local conditions. [ABSTRACT FROM AUTHOR]

Understanding aerosol–cloud–climate interactions in the Arctic is key to predicting the climate in this rapidly changing region. Whilst many studies have focused on submicrometer aerosol (diameter less than 1 µ m), relatively little is known about the supermicrometer aerosol (diameter above 1 µ m). Here, we present a cluster analysis of multiyear (2015–2019) aerodynamic volume size distributions, with diameter ranging from 0.5 to 20 µ m, measured continuously at the Gruvebadet Observatory in the Svalbard archipelago. Together with aerosol chemical composition data from several online and offline measurements, we apportioned the occurrence of the coarse-mode aerosols during the study period (mainly from March to October) to anthropogenic (two sources, 27 %) and natural (three sources, 73 %) origins. Specifically, two clusters are related to Arctic haze with high levels of black carbon, sulfate and accumulation mode (0.1–1 µ m) aerosol. The first cluster (9 %) is attributed to ammonium sulfate-rich Arctic haze particles, whereas the second one (18 %) is attributed to larger-mode aerosol mixed with sea salt. The three natural aerosol clusters were open-ocean sea spray aerosol (34 %), mineral dust (7 %) and an unidentified source of sea spray-related aerosol (32 %). The results suggest that sea-spray-related aerosol in polar regions may be more complex than previously thought due to short- and long-distance origins and mixtures with Arctic haze, biogenic and likely blowing snow aerosols. Studying supermicrometer natural aerosol in the Arctic is imperative for understanding the impacts of changing natural processes on Arctic aerosol. [ABSTRACT FROM AUTHOR]

Measurement and source apportionment of atmospheric pollutants are crucial for the assessment of air quality and the implementation of policies for their improvement. In most cases, such measurements use expensive regulatory-grade instruments, which makes it difficult to achieve wide spatial coverage. Low-cost sensors may provide a more affordable alternative, but their capability and reliability in separating distinct sources of particles have not been tested extensively yet. The present study examines the ability of a low-cost optical particle counter (OPC) to identify the sources of particles and conditions that affect particle concentrations at an urban background site in Birmingham, UK. To help evaluate the results, the same analysis is performed on data from a regulatory-grade instrument (SMPS, scanning mobility particle sizer) and compared to the outcomes from the OPC analysis. The analysis of the low-cost sensor data manages to separate periods and atmospheric conditions according to the level of pollution at the site. It also successfully identifies a number of sources for the observed particles, which were also identified using the regulatory-grade instruments. The low-cost sensor, due to the particle size range measured (0.35 to 40 µ m), performed rather well in differentiating sources of particles with sizes greater than 1 µ m, though its ability to distinguish their diurnal variation, as well as to separate sources of smaller particles, at the site was limited. The current level of source identification demonstrated makes the technique useful for background site studies, where larger particles with smaller temporal variations are of significant importance. This study highlights the current capability of low-cost sensors in source identification and differentiation using clustering approaches. Future directions towards particulate matter source apportionment using low-cost OPCs are highlighted. [ABSTRACT FROM AUTHOR]

The Indian megacity of Delhi suffers from some of the poorest air quality in the world. While ambient NO2 and particulate matter (PM) concentrations have received considerable attention in the city, high ground level ozone (O3) concentrations are an often overlooked component of pollution. O3 can lead to significant ecosystem damage, agricultural crop losses, and adversely affect human health. During October 2018, concentrations of speciated non-methane hydrocarbons volatile organic compounds (C2 -- C13), oxygenated volatile organic compounds (o-VOCs), NO, NO2, HONO, CO, SO2, O3, and photolysis rates, were continuously measured at an urban site in Old Delhi. These observations were used to constrain a detailed chemical box model utilising the Master Chemical Mechanism v3.3.1. VOCs and NOx (NO + NO2) were varied in the model to test their impact on local O3 production rates, P(O3), which revealed a VOC-limited chemical regime. When only NOx concentrations were reduced, a significant increase in P(O3) was observed, thus VOC co-reduction approaches must also be considered in pollution abatement strategies. Of the VOCs examined in this work, mean morning P(O3) rates were most sensitive to monoaromatic compounds, followed by monoterpenes and alkenes, where halving their concentrations in the model led to a 15.6 %, 13.1 % and 12.9 % reduction in P(O3), respectively. P(O3) was not sensitive to direct changes in aerosol surface area but was very sensitive to changes in photolysis rates, which may be influenced by future changes in PM concentrations. VOC and NOx concentrations were divided into emission source sectors, as described by the EDGAR v5.0 Global Air Pollutant Emissions and EDGAR v4.3.2_VOC_spec inventories, allowing for the impact of individual emission sources on P(O3) to be investigated. Reducing road transport emissions only, a common strategy in air pollution abatement strategies worldwide, was found to increase P(O3), even when the source was removed in its entirety. Effective reduction in P(O3) was achieved by reducing road transport along with emissions from combustion for manufacturing and process emissions. Modelled P(O3) reduced by ~ 20 ppb h-1 when these combined sources were halved. This study highlights the importance of reducing VOCs in parallel with NOx and PM in future pollution abatement strategies in Delhi. [ABSTRACT FROM AUTHOR]

Atmospheric aerosols contribute some of the greatest uncertainties to estimates of global radiative forcing and have significant effects on human health. New particle formation (NPF) is the process by which new aerosols of sub-2 nm diameter form from gas-phase precursors and contributes significantly to particle numbers in the atmosphere, accounting for approximately 50 % of cloud condensation nuclei globally. Here, we study summertime NPF in urban Barcelona in north-eastern Spain utilising particle counting instruments down to 1.9 nm and a Nitrate Chemical Ionisation Atmospheric Pressure interface Time of Flight Mass Spectrometer (CI-APi-ToF). The rate of formation of new particles is seen to increase linearly with sulfuric acid concentration, although particle formation rates fall short of chamber studies of H2SO4 –DMA– H2O while exceeding those of H2SO4 –BioOxOrg– H2O nucleation, although a role of highly oxygenated molecules (HOMs) cannot be ruled out. The sulfuric acid dimer : monomer ratio is significantly lower than that seen in experiments involving sulfuric acid and dimethylamine (DMA) in chambers, indicating that stabilisation of sulfuric acid clusters by bases is weaker in this dataset than in chambers, either due to rapid evaporation due to high summertime temperatures or limited pools of stabilising amines. Such a mechanism cannot be verified in these data, as no higher-order H2SO4 –amine clusters nor H2SO4 –HOM clusters were measured. The high concentrations of HOMs arise from isoprene, alkylbenzene, monoterpene and polycyclic aromatic hydrocarbon (PAH) oxidation, with alkylbenzenes providing greater concentrations of HOMs due to significant local sources. The concentration of these HOMs shows a dependence on temperature. The organic compounds measured primarily fall into the semivolatile organic compound (SVOC) volatility class arising from alkylbenzene and isoprene oxidation. Low-volatility organic compounds (LVOCs) largely arise from oxidation of alkylbenzenes, PAHs and monoterpenes, whereas extremely low-volatility organic compounds (ELVOCs) arise from primarily PAH and monoterpene oxidation. New particle formation without growth past 10 nm is also observed, and on these days oxygenated organic concentrations are lower than on days with growth by a factor of 1.6, and thus high concentrations of low-volatility oxygenated organics which primarily derive from traffic-emitted volatile organic compounds (VOCs) appear to be a necessary condition for the growth of newly formed particles in Barcelona. These results are consistent with prior observations of new particle formation from sulfuric acid–amine reactions in both chambers and the real atmosphere and are likely representative of the urban background of many European Mediterranean cities. A role for HOMs in the nucleation process cannot be confirmed or ruled out, and there is strong circumstantial evidence of the participation of HOMs across multiple volatility classes in particle growth. [ABSTRACT FROM AUTHOR]

The Southern Ocean and Antarctic region currently best represent one of the few places left on our planet with conditions similar to the preindustrial age. Currently, climate models have a low ability to simulate conditions forming the aerosol baseline; a major uncertainty comes from the lack of understanding of aerosol size distributions and their dynamics. Contrasting studies stress that primary sea salt aerosol can contribute significantly to the aerosol population, challenging the concept of climate biogenic regulation by new particle formation (NPF) from dimethyl sulfide marine emissions. We present a statistical cluster analysis of the physical characteristics of particle size distributions (PSDs) collected at Halley (Antarctica) for the year 2015 (89 % data coverage; 6–209 nm size range; daily size resolution). By applying the Hartigan–Wong k -mean method we find eight clusters describing the entire aerosol population. Three clusters show pristine average low particle number concentrations (< 121–179 cm -3) with three main modes (30, 75–95 and 135–160 nm) and represent 57 % of the annual PSD (up to 89 %–100 % during winter and 34 %–65 % during summer based on monthly averages). Nucleation and Aitken mode PSD clusters dominate summer months (September–January, 59 %–90 %), whereas a clear bimodal distribution (43 and 134 nm, respectively; Hoppel minimum at mode 75 nm) is seen only during the December–April period (6 %–21 %). Major findings of the current work include: (1) NPF and growth events originate from both the sea ice marginal zone and the Antarctic plateau, strongly suggesting multiple vertical origins, including the marine boundary layer and free troposphere; (2) very low particle number concentrations are detected for a substantial part of the year (57 %), including summer (34 %–65 %), suggesting that the strong annual aerosol concentration cycle is driven by a short temporal interval of strong NPF events; (3) a unique pristine aerosol cluster is seen with a bimodal size distribution (75 and 160 nm, respectively), strongly associated with high wind speed and possibly associated with blowing snow and sea spray sea salt, dominating the winter aerosol population (34 %–54 %). A brief comparison with two other stations (Dome C – Concordia – and King Sejong Station) during the year 2015 (240 d overlap) shows that the dynamics of aerosol number concentrations and distributions are more complex than the simple sulfate–sea-spray binary combination, and it is likely that an array of additional chemical components and processes drive the aerosol population. A conceptual illustration is proposed indicating the various atmospheric processes related to the Antarctic aerosols, with particular emphasis on the origin of new particle formation and growth. [ABSTRACT FROM AUTHOR]

Particle nucleation is one of the main sources of atmospheric particulate matter by number, with new particles having great relevance for human health and climate. Highly oxidized multifunctional organic molecules (HOMs) have been recently identified as key constituents in the growth and, sometimes, in initial formation of new particles. While there have been many studies of HOMs in atmospheric chambers, flow tubes, and clean environments, analyses of data from polluted environments are scarce. Here, measurements of HOMs and particle size distributions down to small molecular clusters are presented alongside volatile organic compounds (VOCs) and trace-gas data from a campaign in June 2017, in Beijing. Many gas-phase HOMs have been characterized and their temporal trends and behaviours analysed in the context of new particle formation. The HOMs identified have a degree of oxidation comparable to that seen in other, cleaner, environments, likely due to an interplay between the higher temperatures facilitating rapid hydrogen abstractions and the higher concentrations of NOx and other RO2⚫ terminators ending the autoxidation sequence more rapidly. Our data indicate that alkylbenzenes, monoterpenes, and isoprene are important precursor VOCs for HOMs in Beijing. Many of the C5 and C10 compounds derived from isoprene and monoterpenes have a slightly greater degree of average oxidation state of carbon compared to those from other precursors. Most HOMs except for large dimers have daytime peak concentrations, indicating the importance of OH⚫ chemistry in the formation of HOMs, as O3 tends to be lower on days with higher HOM concentrations; similarly, VOC concentrations are lower on the days with higher HOM concentrations. The daytime peaks of HOMs coincide with the growth of freshly formed new particles, and their initial formation coincides with the peak in sulfuric acid vapours, suggesting that the nucleation process is sulfuric-acid-dependent, with HOMs contributing to subsequent particle growth. [ABSTRACT FROM AUTHOR]

Aerosols are an integral part of the Arctic climate system due to their direct interaction with radiation and indirect interaction through cloud formation. Understanding aerosol size distributions and their dynamics is crucial for the ability to predict these climate relevant effects. When of favourable size and composition, both long-range-transported – and locally formed particles – may serve as cloud condensation nuclei (CCN). Small changes of composition or size may have a large impact on the low CCN concentrations currently characteristic of the Arctic environment. We present a cluster analysis of particle size distributions (PSDs; size range 8–500 nm) simultaneously collected from three high Arctic sites during a 3-year period (2013–2015). Two sites are located in the Svalbard archipelago: Zeppelin research station (ZEP; 474 m above ground) and the nearby Gruvebadet Observatory (GRU; about 2 km distance from Zeppelin, 67 m above ground). The third site (Villum Research Station at Station Nord, VRS; 30 m above ground) is 600 km west-northwest of Zeppelin, at the tip of north-eastern Greenland. The GRU site is included in an inter-site comparison for the first time. K -means cluster analysis provided eight specific aerosol categories, further combined into broad PSD classes with similar characteristics, namely pristine low concentrations (12 %–14 % occurrence), new particle formation (16 %–32 %), Aitken (21 %–35 %) and accumulation (20 %–50 %). Confined for longer time periods by consolidated pack sea ice regions, the Greenland site GRU shows PSDs with lower ultrafine-mode aerosol concentrations during summer but higher accumulation-mode aerosol concentrations during winter, relative to the Svalbard sites. By association with chemical composition and cloud condensation nuclei properties, further conclusions can be derived. Three distinct types of accumulation-mode aerosol are observed during winter months. These are associated with sea spray (largest detectable sizes, >400 nm), Arctic haze (main mode at 150 nm) and aged accumulation-mode (main mode at 220 nm) aerosols. In contrast, locally produced particles, most likely of marine biogenic origin, exhibit size distributions dominated by the nucleation and Aitken mode during summer months. The obtained data and analysis point towards future studies, including apportioning the relative contribution of primary and secondary aerosol formation processes and elucidating anthropogenic aerosol dynamics and transport and removal processes across the Greenland Sea. In order to address important research questions in the Arctic on scales beyond a singular station or measurement events, it is imperative to continue strengthening international scientific cooperation. [ABSTRACT FROM AUTHOR]

New particle formation (NPF) events have different patterns of development depending on the conditions of the area in which they occur. In this study, particle size distributions in the range of 16.6–604 nm (7 years of data) were analysed and NPF events occurring at three sites of differing characteristics – rural Harwell (HAR), urban background North Kensington (NK), urban roadside Marylebone Road (MR), London, UK – were extracted and studied. The different atmospheric conditions in each study area not only have an effect on the frequency of the events, but also affect their development. The frequency of NPF events is similar at the rural and urban background locations (about 7 % of days), with a high proportion of events occurring at both sites on the same day (45 %). The frequency of NPF events at the urban roadside site is slightly less (6 % of days), and higher particle growth rates (average 5.5 nm h -1 at MR compared to 3.4 and 4.2 nm h -1 at HAR and NK respectively) must result from rapid gas-to-particle conversion of traffic-generated pollutants. A general pattern is found in which the condensation sink increases with the degree of pollution of the site, but this is counteracted by increased particle growth rates at the more polluted location. A key finding of this study is that the role of the urban environment leads to an increment of 20 % in N16–20 nm in the urban background compared to that of the rural area in NPF events occurring at both sites. The relationship of the origin of incoming air masses is also considered and an association of regional events with cleaner air masses is found. Due to lower availability of condensable species, NPF events that are associated with cleaner atmospheric conditions have lower growth rates of the newly formed particles. The decisive effect of the condensation sink in the development of NPF events and the survivability of the newly formed particles is underlined, and influences the overall contribution of NPF events to the number of ultrafine particles in an area. The other key factor identified by this study is the important role that pollution, both from traffic and other sources in the urban environment (such as heating or cooking), plays in new particle formation events. [ABSTRACT FROM AUTHOR]

Some air pollution datasets contain multiple variables with a range of measurement units, and combined analysis using positive matrix factorization (PMF) can be problematic but can offer benefits through the greater information content. In this work, a novel method is devised and the source apportionment of a mixed unit dataset (PM 10 mass and number size distribution, NSD) is achieved using a novel two-step approach to PMF. In the first step the PM 10 data are PMF-analysed using a source apportionment approach in order to provide a solution which best describes the environment and conditions considered. The time series G values (and errors) of the PM 10 solution are then taken forward into the second step, where they are combined with the NSD data and analysed in a second PMF analysis. This results in NSD data associated with the apportioned PM 10 factors. We exemplify this approach using data reported in the study of Beddows et al. (2015), producing one solution which unifies the two separate solutions for PM 10 and NSD data datasets together. We also show how regression of the NSD size bins and the G time series can be used to elaborate the solution by identifying NSD factors (such as nucleation) not influencing the PM 10 mass. [ABSTRACT FROM AUTHOR]

Particle number size distributions have been measured simultaneously by scanning mobility particle sizers (SMPSs) at five sites in central London for a 1 month campaign in January–February 2017. These measurements were accompanied by condensation particle counters (CPCs) to measure total particle number count at four of the sites and Aethalometers measuring black carbon (BC) at five sites. The spatial distribution and inter-relationships of the particle size distribution and SMPS total number counts with CPC total number counts and black carbon measurements have been analysed in detail as well as variations in the size distributions. One site (Marylebone Road) was in a street canyon with heavy traffic, one site (Westminster University) was on a rooftop adjacent to the Marylebone Road sampler, and a further sampler was located at Regent's University within a major park to the north of Marylebone Road. A fourth sampler was located nearby at 160 m above ground level on the BT tower and a fifth sampler was located 4 km to the west of the main sampling region at North Kensington. Consistent with earlier studies it was found that the mode in the size distribution had shifted to smaller sizes at the Regent's University (park) site, the mean particle shrinkage rate being 0.04 nm s -1 with slightly lower values at low wind speeds and some larger values at higher wind speeds. There was evidence of complete evaporation of the semi-volatile nucleation mode under certain conditions at the elevated BT Tower site. While the SMPS total count and black carbon showed typical traffic-dominated diurnal profiles, the CPC count data typically peaked during night-time as did CPC/SMPS and CPC/BC ratios. This is thought to be due to the presence of high concentrations of small particles (2.5–15 nm diameter) probably arising from condensational growth from traffic emissions during the cooler night-time conditions. Such behaviour was most marked at the Regent's University and Westminster University sites and less so at Marylebone Road, while at the elevated BT Tower site the ratio of particle number (CPC) to black carbon peaked during the morning rush hour and not at night-time, unlike the other sites. An elevation in nucleation mode particles associated with winds from the west and WSW sector was concluded to result from emissions from London Heathrow Airport, despite a distance of 22 km from the central London sites. [ABSTRACT FROM AUTHOR]

The vertical profile of new particle formation (NPF) events was studied by comparing the aerosol size number distributions measured aloft and at surface level in a suburban environment in Madrid, Spain, using airborne instruments. The horizontal distribution and regional impact of the NPF events was investigated with data from three urban, urban background, and suburban stations in the Madrid metropolitan area. Intensive regional NPF episodes followed by particle growth were simultaneously recorded at three stations in and around Madrid during a field campaign in July 2016. The urban stations presented larger formation rates compared to the suburban station. Condensation and coagulation sinks followed a similar evolution at all stations, with higher values at urban stations. However, the total number concentration of particles larger than 2.5 nm was lower at the urban station and peaked around noon, when black carbon (BC) levels are at a minimum. The vertical soundings demonstrated that ultrafine particles (UFPs) are formed exclusively inside the mixed layer. As convection becomes more effective and the mixed layer grows, UFPs are detected at higher levels. The morning soundings revealed the presence of a residual layer in the upper levels in which aged particles (nucleated and grown on previous days) prevail. The particles in this layer also grow in size, with growth rates significantly smaller than those inside the mixed layer. Under conditions with strong enough convection, the soundings revealed homogeneous number size distributions and growth rates at all altitudes, which follow the same evolution at the other stations considered in this study. This indicates that UFPs are detected quasi-homogenously in an area spanning at least 17 km horizontally. The NPF events extend over the full vertical extension of the mixed layer, which can reach as high as 3000m in the area, according to previous studies. On some days a marked decline in particle size (shrinkage) was observed in the afternoon, associated with a change in air masses. Additionally, a few nocturnal nucleation-mode bursts were observed at the urban stations, for which further research is needed to elucidate their origin. [ABSTRACT FROM AUTHOR]

NPF events have different patterns of development depending on the conditions of the area in which they occur. In this study, NPF events occurring at three sites of differing characteristics (rural Harwell (HAR), urban background North Kensington (NK), urban roadside Marylebone Road (MR), London, UK) were studied (seven years of data). The different atmospheric conditions in each study area not only have an effect on the frequency of the events, but also affect their development. The frequency of NPF events is similar at the rural and urban background locations (about 7% of days), with a high proportion of events occurring at both sites on the same day (45%). The frequency of NPF events at the urban roadside site is slightly less (6% of days), and higher particle growth rates (average 5.5nmh−1 at MR compared to 3.4nmh−1 and 4.2nmh−1 at HAR and NK respectively) must result from rapid gas to particle conversion of traffic-generated pollutants. A general pattern is found in which the condensation sink increases with the degree of pollution of the site, but this is counteracted by increased particle growth rates at the more polluted location. A key finding of this study is that the role of the urban environment leads to an increment of 20% in N16–20nm in the urban background compared to that of the rural area in NPF events occurring at both sites. The relationship of the origin of incoming air masses is also considered and an association of regional events with cleaner air masses is found. Due to lower availability of condensable species, NPF events that are associated with cleaner atmospheric conditions have lower growth rates of the newly formed particles. The decisive effect of the condensation sink in the development of NPF events and the survivability of the newly formed particles is underlined, and influences the overall contribution of NPF events to the number of ultrafine particles in an area. The other key factor identified by this study is the important role that urban pollution plays in new particle formation events. [ABSTRACT FROM AUTHOR]

Atmospheric new particle formation (NPF) is an important phenomenon in terms of global particle number concentrations. Here we investigated the frequency of NPF, formation rates of 10 nm particles, and growth rates in the size range of 10-25 nm using at least 1 year of aerosol number size-distribution observations at 36 different locations around the world. The majority of these measurement sites are in the Northern Hemisphere. We found that the NPF frequency has a strong seasonal variability. At the measurement sites analyzed in this study, NPF occurs most frequently in March-May (on about 30% of the days) and least frequently in December-February (about 10% of the days). The median formation rate of 10 nm particles varies by about 3 orders of magnitude (0.01-10 cm-3 s-1) and the growth rate by about an order of magnitude (1-10 nm h-1). The smallest values of both formation and growth rates were observed at polar sites and the largest ones in urban environments or anthropogenically influenced rural sites. The correlation between the NPF event frequency and the particle formation and growth rate was at best moderate among the different measurement sites, as well as among the sites belonging to a certain environmental regime. For a better understanding of atmospheric NPF and its regional importance, we would need more observational data from different urban areas in practically all parts of the world, from additional remote and rural locations in North America, Asia, and most of the Southern Hemisphere (especially Australia), from polar areas, and from at least a few locations over the oceans. [ABSTRACT FROM AUTHOR]

Particle number size distributions have been measured simultaneously by Scanning Mobility Particle Sizers (SMPS) at five sites in Central London for a one month campaign in January-February 2017. These measurements were accompanied by condensation particle counters (CPC) to measure total particle number count at four of the sites and aethalometers measuring Black Carbon (BC) at five sites. The spatial distribution and inter-relationships of the particle size distribution and SMPS total number counts with CPC total number counts and Black Carbon measurements have been analysed in detail as well as variations in the size distributions. One site (Marylebone Road) was in a heavily-trafficked street canyon, one site (Westminster University) was on a rooftop adjacent to the Marylebone Road sampler, a further sampler was located at Regent's University within a major park to the north of Marylebone Road. A fourth sampler was located nearby at 160 m above ground level on the BT tower and a fifth sampler was located 4 km to the west of the main sampling region at North Kensington. Consistent with earlier studies it was found that the mode in the size distribution had shifted to smaller sizes at the Regent's University (park) site, the mean particle shrinkage rate being 0.04 nm s-1 with slightly lower values at low wind speeds and some larger values at higher wind speeds. There was evidence of complete evaporation of the semi-volatile nucleation mode under certain conditions at the elevated BT Tower site. Whereas SMPS total count and Black Carbon showed typical traffic-dominated diurnal profiles, the CPC count data typically peaked during nighttime as did CPC/SMPS and CPC/BC ratios. This is thought to be due to the presence of high concentrations of small particles (2.5-15 nm diameter) probably arising from condensational growth from traffic emissions during the cooler nighttime conditions. Such behaviour was most marked at the Regent's University and Westminster University sites and less so at Marylebone Road, while at the elevated BT Tower site the ratio of particle number (CPC) to Black Carbon peaked during the morning rush hour and not at nighttime, unlike the other sites. An elevation in nucleation mode particles associated with winds from the West and WSW sector was concluded to result from emissions from London Heathrow Airport, despite a distance of 22 km from the Central London sites. [ABSTRACT FROM AUTHOR]

Some air pollution datasets contain multiple variables with a range of measurement units, and combined analysis by Positive Matrix Factorization (PMF) is problematic, but can offer benefits from the greater information content. In this work, a novel method is devised and the source apportionment of a mixed unit data set (PM10 mass and Number Size Distribution NSD) is achieved using a novel two-step approach to PMF. In the first step the PM10 data is PMF analysed using a source apportionment approach in order to provide a solution which best describes the environment and conditions considered. The time series G values (and errors) of the PM10 solution are then taken forward into the second step where they are combined with the NSD data and analysed in a second PMF analysis. This results in apportioned NSD data associated with the PM10 factors. We exemplify this approach using data reported in the study of Beddows et al. (2015), producing one solution which unifies the two separate solutions for PM10 and NSD data datasets together. We also show how regression of the NSD size bins and the G time series can be used to elaborate the solution by identifying NSD factors (such as nucleation) not influencing the PM10 mass. [ABSTRACT FROM AUTHOR]

Understanding aerosol size distributions is crucial to our ability to predict aerosol number concentrations. When of favourable size and composition, both long range transported particles as well as locally formed ones may serve as Cloud Condensation Nuclei (CCN); small changes may have a large impact on the low CCN concentrations currently characteristic of the Arctic environment. Here, we present a cluster analysis of particle size distributions (PSD, size range 8-500 nm) simultaneously collected from three high Arctic sites across Europe during a three year period (2013-2015). Two sites are located in the Svalbard archipelago: Zeppelin research station (474 m above ground), and the nearby Gruvebadet Observatory (about 2 km distance from Zepplelin, 67 m above ground). The third site (Villum Research Station - Station Nord, 30 m above ground) is 600 km to the west-northwest of Zeppelin, at the tip of north-eastern Greenland. An inter-site comparison exercise is carried out for the first time including the Gruvebadet site. K-means analysis provided eight specific aerosol categories, further combined into broad PSD with similar characteristics, namely: pristine low concentrations (12-14 %), new particle formation (16-32 %), Aitken (21-35 %) and accumulation (20-50 %). Confined for longer time periods by consolidated pack sea ice regions, the Greenland site shows PSD with lower ultrafine mode aerosol concentrations during summer, but higher accumulation mode aerosol concentrations during winter relative to the Svalbard sites. By association with chemical composition and Cloud Condensation Nuclei properties, further conclusions can be derived. Three distinct types of accumulation mode aerosol are observed during winter months, associated with sea spray (largest detectable sizes), Arctic haze (main mode at 150 nm) and aged accumulation mode (main mode at 220 nm) aerosols. In contrast, locally produced and most likely of marine biogenic origin particles exhibit size distributions dominated by the nucleation and Atiken mode aerosol during summer months. The obtained data and analysis set now the stage for future studies; including apportioning the relative contribution of primary and secondary aerosol formation processes to the aerosol size distribution in high Arctic, and elucidating anthropogenic aerosol dynamics, transport and removal processes across the Greenland sea. In a region of enormous importance for future climate on Earth, it is imperative to continue strengthening international scientific cooperation, in order to address important research questions on scales beyond singular station or measurement events. [ABSTRACT FROM AUTHOR]

The international airport of Heathrow is a major source of nitrogen oxides, but its contribution to the levels of sub-micrometre particles is unknown and is the objective of this study. Two sampling campaigns were carried out during warm and cold seasons at a site close to the airfield (1.2 km). Size spectra were largely dominated by ultrafine particles: nucleation particles (< 30 nm) were found to be ~ 10 times higher than those commonly measured in urban background environments of London. Five clusters and six factors were identified by applying k means cluster analysis and positive matrix factorisation (PMF), respectively, to particle number size distributions; their interpretation was based on their modal structures, wind directionality, diurnal patterns, road and airport traffic volumes, and on the relationship with weather and other air pollutants. Airport emissions, fresh and aged road traffic, urban accumulation mode, and two secondary sources were then identified and apportioned. The fingerprint of Heathrow has a characteristic modal structure peaking at < 20 nm and accounts for 30-35 % of total particles in both the seasons. Other main contributors are fresh (24-36 %) and aged (16-21 %) road traffic emissions and urban accumulation from London (around 10 %). Secondary sources accounted for less than 6 % in number concentrations but for more than 50 % in volume concentration. The analysis of a strong regional nucleation event showed that both the cluster categorisation and PMF contributions were affected during the first 6h of the event. In 2016, the UK government provisionally approved the construction of a third runway; therefore the direct and indirect impact of Heathrow on local air quality is expected to increase unless mitigation strategies are applied successfully. [ABSTRACT FROM AUTHOR]

Major airports are often located within or close to large cities; their impacts on the deterioration of air quality at ground level are amply recognised. The international airport of Heathrow is a major source of nitrogen oxides in the Greater London area, but its contribution to the levels of submicrometre particles is unknown, and is the objective of this study. Two sampling campaigns were carried out during warm and cold seasons at a site close to the airfield (1.2 km). Size spectra were largely dominated by ultrafine particles: nucleation particles (< 30 nm) were found to be ~ 10 times higher than those commonly measured in urban background environments of London. A set of chemometric tools was used to discern the pollution arising from aircraft operations and those from other sources within the city or from the traffic generated by the airport. Five clusters and 6 factors were identified by applying k-means cluster analysis and positive matrix factorization (PMF) respectively to particle number size distributions; their interpretation was based on their modal structures, wind directionality, diurnal patterns, road and airport traffic volumes and on the relationship with weather and other air pollutants. Airport emissions, fresh and aged road traffic, urban accumulation mode and two secondary sources were then identified and apportioned. The comparison of cluster and PMF analyses allowed extraction of further information. The analysis of a strong regional nucleation event was also performed to detect its effect upon concentrations. The fingerprint of Heathrow has a characteristic modal structure peaking at < 20 nm and accounts for 30-35 % of total particles in both the seasons. Other main contributors are fresh (24-36 %) and aged (16-21 %) road traffic emissions and urban accumulation from London (around 10 %). Secondary sources accounted for less than 6 % in number concentrations but for more than 50 % in volume concentration. In 2016, the UK government provisionally approved the construction of a third runway; therefore the direct and indirect impact of Heathrow on local air quality is expected to increase unless mitigation strategies are applied successfully. [ABSTRACT FROM AUTHOR]

The aerosol time-of-flight mass spectrometer (ATOFMS) provides size-resolved information on the chemical composition of single particles with high time resolution. Within SAPUSS (Solving Aerosol Problems by Using Synergistic Strategies), continuous ATOFMS measurements of ambient particles were made simultaneously at two urban locations: urban background (UB) site and roadside (RS) site in the city of Barcelona (Spain) from 17 September to 18 October 2010. Two different instrumental configurations were used: ATOFMS (TSI 3800) with a converging nozzle inlet (high efficiency at about 800-2000 nm) at the UB site and ATOFMS (TSI 3800-100) with an aerodynamic lens inlet (high efficiency at about 300-700 nm) at the RS site. This is the first time, to our knowledge, that two ATOFMS instruments have been deployed in the same field study. The different instrument configurations had an impact on the observed particle types at the two sites. Nevertheless, 10 particle types were detected at both locations, including local and regional elemental carbon (22.7-58.9% of total particles), fresh and aged sea salt (1.0-14.6%), local and regional nitrate-containing aerosols (3-11.6%), local lead-containing metallic particles (0.1-0.2%), and transported Fe-nitrate particles (0.8-2.5%). The ATOFMS at the UB also characterized four particle types: calcium-containing dust (0.9%), Saharan dust (1.3%), vanadium-containing particles (0.9%), and vegetative debris (1.7%). By contrast, the high statistical counts of fine particles detected at the RS allowed identification of eight particle types. Four of these contained organic nitrogen of primary and secondary origin, which highlights the complex nature of the sources and processes that contribute to this aerosol chemical component. Aminium salts were found related to coarse sulfate-rich particle types, suggesting heterogeneous reaction mechanisms for their formation. The other four particle types mainly containing organic carbon were found spiking at different types of the day, also showing a complex single-particle mixing state relationship between organic carbon and nitrate. This ATOFMS study clearly shows that the composition of atmospheric fine particles in Barcelona, and likely other Mediterranean urban areas, is complex, with a wide range of local and regional sources combining with chemical processing to produce at least 22 different particle types exhibiting different temporal behaviour. The advantage of using two ATOFMS instruments is also demonstrated, with the nozzle-skimmer configuration enabling detection of coarse dust particles and the aerodynamic lens configuration allowing better identification of particles rich in organic carbon and amines. Overall, we find that organic nitrogen is a considerable fraction of the single particles detected, especially at the traffic-dominated RS site. Further studies are needed, especially at high time resolution, to better understand the sources and properties of particulate organic nitrogen. [ABSTRACT FROM AUTHOR]

The Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) provides size resolved information on the chemical composition of single particles with high time resolution. Within SAPUSS (Solving Aerosol Problems by Using Synergistic Strategies), continuous ATOFMS measurements of ambient particles were made simultaneously at two urban locations: urban background (UB) site and road side (RS) site in the city of Barcelona (Spain) from 17th September to 18th October 2010. Two different instrumental configurations were used: ATOFMS (TSI 3800) with a converging nozzle inlet (high efficiency at about 800-2000nm) at the UB site and ATOFMS (TSI 3800-100) with an aerodynamic lens inlet (high efficiency at about 300-700nm) at the RS site. This is the first time, to our knowledge, that two ATOFMS instruments have been deployed in the same field study. The different instrument configurations had an impact on the observed particle types at the two sites. Nevertheless, ten particle types were detected at both locations, including local and regional elemental carbon (22.7-58.9% of total particles), fresh and aged sea salt (1.0-14.6%), local and regional nitrate -containing aerosols (3-11.6%), local lead-containing metallic particles (0.1-0.2%) and transported Fe-nitrate particles (0.8-2.5%). The ATOFMS at the UB also characterised four particle types: calcium-containing dust (0.9%), Saharan dust (1.3%), vanadium-containing particles (0.9%) and vegetative debris (1.7%). By contrast, the high statistical counts of fine particles detected at the RS allowed identification of eight particle types. Four of these contained amines of primary and secondary origin. Aminium salts were found related to coarse sulphate rich particle types, suggesting heterogeneous reaction mechanisms for their formation. The other four particle types mainly containing organic carbon were found spiking at different types of the day, showing a complex single particle mixing state relationship between organic carbon and nitrate. This ATOFMS study clearly shows that the composition of atmospheric fine particles in Barcelona, and likely other Mediterranean urban areas, is complex, with a wide range of local and regional sources combining with chemical processing to produce at least twenty-two different particle types exhibiting different temporal behaviour. The advantage of using two ATOFMS instruments is also demonstrated, with the nozzle-skimmer configuration enabling detection of coarse dust particles and the aerodynamic lens configuration allowing better identification of particles rich in organic carbon and amines. [ABSTRACT FROM AUTHOR]

There is a paucity of quantitative knowledge on the contributions of non-exhaust (abrasion and re-suspension) sources to traffic emissions. Abrasive emissions can be broadly categorised as tyre wear, brake wear and road dust/road surface wear. Current research often considers road dust and tyre dust as externally mixed particles, the former mainly composed of mineral matter and the latter solely composed of mainly organic matter and some trace elements. The aim of this work was to characterise tyre wear from both laboratory and field studies by using Aerosol Time-Of-Flight Mass Spectrometry (ATOFMS). Real-time single particle chemical composition was obtained from a set of rubber tyres rotating on a metal surface. Bimodal particle number size distributions peaking at 35 nm and 85 nm were obtained from SMPS/APS measurements over the range 6-20,000 nm. ATOFMS mass spectra of tyre wear in the particle size range 200-3000 nm diameter show peaks due to exo-sulphur compounds, nitrate, Zn and ions of high molecular weight (m/z > 100) attributed to organic polymers. Two large ATOFMS datasets collected from a number of outdoor studies were examined. The former was constituted of 48 road dust samples collected on the roads of London. The latter consisted of ATOFMS ambient air field studies from Europe, overall composed of more than 2,000,000 single particle mass spectra. The majority (95%) of tyre wear particles present in the road dust samples and atmospheric samples are internally mixed with metals (Li, Na, Ca, Fe, Ti), as well as phosphate. It is concluded that the interaction of tyres with the road surface creates particles internally mixed from two sources: tyre rubber and road surface materials. Measurements of the tyre rubber component alone may underestimate the contribution of tyre wear to concentrations of airborne particulate matter. The results presented are especially relevant for urban aerosol source apportionment and PM2.5 exposure assessment. [ABSTRACT FROM AUTHOR]

Ground-level ozone (O3) levels are usually lower in urban centers than nearby rural sites. To compare trends in O3 levels during the period 1990-2010, we obtained monitoring data from paired urban and rural sites from the European Environment Agency and the US Environmental Protection Agency. Ozone peaks decreased at both station types, with no significant differences between urban and rural stations. Ozone annual averages increased at both urban and rural sites, with a faster rate of increase for urban centers. The overall trend was for convergence between urban and rural O3 data. Ozone levels exceeded the criteria established for the protection of human and vegetation health at both urban and rural sites. [ABSTRACT FROM AUTHOR]

Particle number concentration data have been collected on a very busy road in central London (Marylebone Road). Continuous size distributions from 15 nm to 10 μm diameter, collected over 21 days, were analyzed using positive matrix factorization which identified 10 factors, five of which were observed to make major contributions (greater than 8%) to either the total number or volume of particulate matter. The sources associated with each factor were identified from the size distribution, directional association, diurnal variation and their relationship to meteorological pollution and traffic volume variables. The factors related to the emissions on Marylebone Road accounted for 40.5% of particle volume and 71.9% of particle number. These comprised nucleation mode exhaust particles (3.6% of total volume and 27.4% of total number), solid mode exhaust particles (18.8% of total volume and 38.0% of total number), brake dust (13.7% of total volume and 1.7% of total number and resuspension (4.4% of total volume and 4.8% of total number). Another six factors were associated with the urban background accounting for 59.5% of total volume and 28.2% of total particle number count. The method is extremely successful at separating the components of on-road emissions including brake wear and resuspension. [ABSTRACT FROM AUTHOR]

Particle size is a key determinant of the hazard posed by airborne particles. Continuous multivariate particle size data have been collected using aerosol particle size spectrometers sited at four locations within the UK: Harwell (Oxfordshire); Regents Park (London); British Telecom Tower (London); and Marylebone Road (London). These data have been analyzed using k-means cluster analysis, deduced to be the preferred cluster analysis technique, selected from an option of four partitional cluster packages, namely the following: Fuzzy; k-means; k-median; and Model-Based clustering. Using cluster validation indices k-means clustering was shown to produce clusters with the smallest size, furthest separation, and importantly the highest degree of similarity between the elements within each partition. Using k-means clustering, the complexity of the data set is reduced allowing characterization of the data according to the temporal and spatial trends of the clusters. At Harwell, the rural background measurement site, the cluster analysis showed that the spectra may be differentiated by their modal-diameters and average temporal trends showing either high counts during the day-time or night-time hours. Likewise for the urban sites, the cluster analysis differentiated the spectra into a small number of size distributions according their modal-diameter, the location of the measurement site, and time of day. The responsible aerosol emission, formation, and dynamic processes can be inferred according to the cluster characteristics and correlation to concurrently measured meteorological, gas phase, and particle phase measurements. [ABSTRACT FROM AUTHOR]