Particle Number Size Distribution Measurements Research Articles

Evaluation of a Partector Pro for atmospheric particle number size distribution and number concentration measurements at an urban background site

Abstract. Particle number size distributions, total number concentrations and mean particle sizes have been measured for 70 d at an urban background site in Mülheim-Styrum, Germany, with a handheld Partector Pro of the first generation and a TSI mobility particle size spectrometer (MPSS). The aim of the study was to evaluate the performance of the Partector Pro against the MPSS. The results show that the size distributions, measured with the Partector Pro, agree with the MPSS mostly within ± 25 % for particle sizes between 10 and 113.5 nm, whereas higher, systematic differences were observed for larger particles. The measurement accuracy was shown to be dependent on the geometric mean diameter and the geometric standard deviation of the aerosol. Best results were found for the most abundant size distributions with geometric mean particle diameters ≥ 30 nm and geometric standard deviations larger than 1.8. The total number concentration, measured by the Partector Pro, was found to be in excellent agreement with the MPSS with a slope of the linear fit of 0.9977 and a regression coefficient of R2=0.9956. The agreement of the geometric mean particle diameter, determined with the Partector Pro and the MPSS was good but moderately dependent on the particle size distribution. For mean particle sizes between 20 and 50 nm, the bias was within ±15 %. Higher deviations of up to 30 % were observed when the geometric mean particle sizes exceeded 70 nm and when the geometric standard deviations exceeded approximately 2.7.

Significant spatial gradients in new particle formation frequency in Greece during summer

Abstract. Extensive continuous particle number size distribution measurements took place during two summers (2020 and 2021) at 11 sites in Greece for the investigation of the frequency and the spatial extent of new particle formation (NPF). The study area is characterized by high solar intensity and fast photochemistry and has moderate to low fine particulate matter levels during the summer. The average PM2.5 levels were relatively uniform across the examined sites. The NPF frequency during summer varied from close to zero in the southwestern parts of Greece to more than 60 % in the northern, central, and eastern regions. The mean particle growth rate for each station varied between 3.4 and 8 nm h−1, with an average rate of 5.7 nm h−1. At most of the sites there was no statistical difference in the condensation sink between NPF event and non-event days, while lower relative humidity was observed during the events. The high-NPF-frequency sites in the north and northeast were in close proximity to both coal-fired power plants (high emissions of SO2) and agricultural areas with some of the highest ammonia emissions in the country. The southern and western parts of Greece, where NPF was infrequent, were characterized by low ammonia emissions, while moderate levels of sulfuric acid were estimated (107 molec. cm−3) in the west. Although the emissions of biogenic volatile organic compounds were higher in western and southern sectors, they did not appear to lead to enhanced frequency of NPF. The infrequent events at these sites occurred when the air masses had spent a few hours over areas with agricultural activities and thus elevated ammonia emissions. Air masses arriving at the sites directly from the sea were not connected with atmospheric NPF. These results support the hypothesis that ammonia and/or amines limit new particle formation in the study area.

Characterization of ultrafine particles and the occurrence of new particle formation events in an urban and coastal site of the Mediterranean area

Abstract. In this work, new particle formation events (NPFs) occurring at two locations in southern Italy, the urban background site of Lecce (ECO station) and the coastal site of Lamezia Terme (LMT station), are identified and analyzed. The study aims to compare the properties of NPF events at the two sites, located 225 km away from each other and characterized by marked differences in terms of emission sources and local weather dynamics. Continuous measurements of particle number size distributions, in the size range from 10 to 800 m, were performed at both sites by a mobility particle size spectrometer (MPSS). The occurrence of NPF events, observed throughout the study period that lasted 5 years, produced different results in terms of frequency of occurrence: 25 % of the days at ECO and 9 % at LMT. NPF events showed seasonal patterns: higher frequency during spring and summer at the urban background site and the autumn–winter period at the coastal site. Some of these events happened simultaneously at both sites, indicating the occurrence of the nucleation process on a large spatial scale. Cluster analysis of 72 h back trajectories showed that during the NPF events the two stations were influenced by similar air masses, most of which originated from the north-western direction. Local meteorological conditions characterized by high pressure, with a prevalence of clear skies, low levels of relative humidity (RH < 52 %), and moderate winds (3–4 m s−1) dominated the NPF events at both sites. Notable differences were observed in SO2 and PM2.5 concentrations and H2SO4 proxy levels, resulting in ∼65 %, ∼80 %, and 50 % lower levels at LMT compared to ECO, respectively. It is likely that the lower level of that which is recognized as one of the main gas precursors involved in the nucleation process could be responsible for the smaller NPF frequency of occurrence (∼60 % less than ECO) observed in LMT.

Comparative Study on the Friction Behaviour and the Particle Formation Process between a Laser Cladded Brake Disc and a Conventional Grey Cast Iron Disc

Brake-wear particle emissions are the result of the components of a friction brake being in tribological contact, and they are classified as non-exhaust emissions. Since most of the emitted particles belong to the size classes of particulate matter (≤10 μm) and differ significantly in terms of their physico-chemical properties from automotive exhaust emissions, this source is of particular relevance to human health and, therefore, the focus of scientific studies. Previous studies have shown that coated brake discs offer significant wear and emission reduction potential. Nevertheless, no studies are available that describe the specific particle formation process, the contact conditions, the structure of the friction layer and the differences compared to conventional grey cast iron discs. The aim of this study is to describe those differences. For this purpose, the tribological behaviour, the structure of the friction layer and the associated particle dynamics within the friction contact between a laser cladding coated disc and a conventional grey cast iron disc are compared. The required investigations are carried out both ex situ (stationary) and in situ (dynamic). Parallel to the tribological investigations, the particle emission behaviour is determined on an inertia dynamometer using a constant volume sampling system (CVS) and equipment for particle number and particle size distribution measurement. The results show that, for two different brake pads, the laser cladding brake disc has lower wear and less particulate emissions than the grey cast iron brake disc. The wear behaviour of the coating varies significantly for the two brake pads. By contrast, the grey cast iron brake disc shows a significantly lower influence.

Impact of urban aerosols on the cloud condensation activity using a clustering model

The indirect effect of aerosols on climate through aerosol-cloud-interactions is still highly uncertain and limits our ability to assess anthropogenic climate change. The foundation of this uncertainty is in the number of cloud condensation nuclei (CCN), which itself mainly stems from uncertainty in aerosol sources and how particles evolve to become effective CCN. We analyze particle number size distribution (PNSD) and CCN measurements from an urban site in a two-step method: (1) we use an unsupervised clustering model to classify the main aerosol categories and processes occurring in the urban atmosphere and (2) we explore the influence of the identified aerosol populations on the CCN properties. According to the physical properties of each cluster, its diurnal timing, and additional air quality parameters, the clusters are grouped into five main aerosol categories: nucleation, growth, traffic, aged traffic, and urban background. The results show that, despite aged traffic and urban background categories are those with lower total particle number concentrations (Ntot) these categories are the most efficient sources in terms of contribution to the overall CCN budget with activation fractions (AF) around 0.5 at 0.75 % supersaturation (SS). By contrast, road traffic is an important aerosol source with the highest frequency of occurrence (32 %) and relatively high Ntot, however, its impact in the CCN activity is very limited likely due to lower particle mean diameter and hydrophobic chemical composition. Similarly, nucleation and growth categories, associated to new particle formation (NPF) events, present large Ntot with large frequency of occurrence (22 % and 28 %, respectively) but the CCN concentration for these categories is about half of the CCN concentration observed for the aged traffic category, which is associated with their small size. Overall, our results show that direct influence of traffic emissions on the CCN budget is limited, however, when these particles undergo ageing processes, they have a significant influence on the CCN concentrations and may be an important CCN source. Thus, aged traffic particles could be transported to other environments where clouds form, triggering a plausible indirect effect of traffic emissions on aerosol-cloud interactions and consequently contributing to climate change.

Aerosol optical properties calculated from size distributions, filter samples and absorption photometer data at Dome C, Antarctica, and their relationships with seasonal cycles of sources

Abstract. Optical properties of surface aerosols at Dome C, Antarctica, in 2007–2013 and their potential source areas are presented. Scattering coefficients (σsp) were calculated from measured particle number size distributions with a Mie code and from filter samples using mass scattering efficiencies. Absorption coefficients (σap) were determined with a three-wavelength Particle Soot Absorption Photometer (PSAP) and corrected for scattering by using two different algorithms. The scattering coefficients were also compared with σsp measured with a nephelometer at the South Pole Station (SPO). The minimum σap was observed in the austral autumn and the maximum in the austral spring, similar to other Antarctic sites. The darkest aerosol, i.e., the lowest single-scattering albedo ωo≈0.91, was observed in September and October and the highest ωo≈0.99 in February and March. The uncertainty of the absorption Ångström exponent αap is high. The lowest αap monthly medians were observed in March and the highest in August–October. The equivalent black carbon (eBC) mass concentrations were compared with eBC measured at three other Antarctic sites: the SPO and two coastal sites, Neumayer and Syowa. The maximum monthly median eBC concentrations are almost the same (∼3±1 ng m−3) at all these sites in October–November. This suggests that there is no significant difference in eBC concentrations between the coastal and plateau sites. The seasonal cycle of the eBC mass fraction exhibits a minimum f(eBC) ≈0.1 % in February–March and a maximum ∼4 %–5 % in August–October. Source areas were calculated using 50 d FLEXPART footprints. The highest eBC concentrations and the lowest ωo were associated with air masses coming from South America, Australia and Africa. Vertical simulations that take BC particle removal processes into account show that there would be essentially no BC particles arriving at Dome C from north of latitude 10∘ S at altitudes <1600 m. The main biomass-burning regions Africa, Australia and Brazil are more to the south, and their smoke plumes have been observed at higher altitudes than that, so they can get transported to Antarctica. The seasonal cycle of BC emissions from wildfires and agricultural burning and other fires in South America, Africa and Australia was calculated from data downloaded from the Global Fire Emissions Database (GFED). The maximum total emissions were in August–September, but the peak of monthly average eBC concentrations is observed 2–3 months later in November, not only at Dome C, but also at the SPO and the coastal stations. The air-mass residence-time-weighted BC emissions from South America are approximately an order of magnitude larger than from Africa and Oceania, suggesting that South American BC emissions are the largest contributors to eBC at Dome C. At Dome C the maximum and minimum scattering coefficients were observed in austral summer and winter, respectively. At the SPO σsp was similar to that observed at Dome C in the austral summer, but there was a large difference in winter, suggesting that in winter the SPO is more influenced by sea-spray emissions than Dome C. The seasonal cycles of σsp at Dome C and at the SPO were compared with the seasonal cycles of secondary and primary marine aerosol emissions. The σsp measured at the SPO correlated much better with the sea-spray aerosol emission fluxes in the Southern Ocean than σsp at Dome C. The seasonal cycles of biogenic secondary aerosols were estimated from monthly average phytoplankton biomass concentrations obtained from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite sensor data. The analysis suggests that a large fraction of the biogenic scattering aerosol observed at Dome C has been formed in the polar zone, but it may take a month for the aerosol to be formed, be grown and get transported from the sea level to Dome C.

Estimation of the Seasonal Inhaled Deposited Dose of Particulate Matter in the Respiratory System of Urban Individuals Living in an Eastern Mediterranean City.

In this study, we present an estimation for the inhaled deposited dose rate in adult males and females during common exposure scenarios to urban background aerosols in an Eastern Mediterranean city (Amman, Jordan) based on a one-year database of measured particle number size distribution. The dose rates show seasonal variations reflecting the physical characteristics (i.e., modal structure) of the particle number size distribution. An additional factor was the varying deposition fraction (DF) for different regions and different human activities (exercising versus resting). The total dose rate was 3 × 109–65 × 109 particles/h (PM2.5 and PM10 doses 1–22 µg/h and 9–210 µg/h; respectively) depending on the gender, activity, and season. Based on the particle number metrics, the inhaled deposited dose in the head, Tracheobronchial, and alveolar were 7–16%, 16–28%, and 56–76%; respectively. Based on the PM2.5 metric, the corresponding dose rate was 9–41%,13–19%; and 46–72% respectively. As for the PM10 metric, they were 25–75%, 7–35%, and 15–55%; respectively.

Historically understanding the spatial distributions of particle surface area concentrations over China estimated using a non-parametric machine learning method

A non-parametric ensemble model was proposed to estimate the long-term (2015–2019) particle surface area concentrations (SA) over China for the first time on basis of a vilification dataset of measured particle number size distribution. This ensemble model showed excellent cross-validation R2 value (CV R2 = 0.83) as well as a relatively low root-mean-square error (RMSE = 195.0 μm2/cm3). No matter in which year, considerable spatial heterogeneity of SA was found over China with higher SA in Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD), and Middle Lower Reaches of Yangtze River (MLYR). From 2015 to 2019, SA significantly decreased in representative city clusters. The reduction rates were 140.1 μm2·cm−3·a−1 in BTH, 110.7 μm2·cm−3·a−1 in Pearl River Delta (PRD), 105.2 μm2·cm−3·a−1 in YRD, and 92.4 μm2·cm−3·a−1 in Sichuan Basin (SCB), respectively. Even though such quick reduction, high SA (ranged from ~800 μm2/cm3 to ~1750 μm2/cm3) during the heavy pollution period (PM2.5 > 75 μg/m3) still existed in the above-mentioned city clusters and may provide rich reaction vessels for multiphase chemistry. A dichotomy of enhanced annual 4th maximum daily 8-h average O3 concentrations (4MDA8 O3) and decreased SA during summertime was found in Shanghai, a representative city of YRD. In Chengdu (SCB), increased 4MDA8 O3 concentration was associated with a synchronous increase of SA from 2017 to 2019. Differently, 4MDA8 O3 concentrations enhanced in Beijing (BTH) and Guangzhou (PRD), while not significant for SA before 2018. This work will greatly deepen our understanding of the historical variation and spatial distributions of SA over China.

Reduction in Anthropogenic Emissions Suppressed New Particle Formation and Growth: Insights From the COVID‐19 Lockdown

AbstractTo control the spread of the novel 2019 Coronavirus (COVID‐19), the Government of India enforced nationwide social and transportation restrictions (lockdown) in three phases from the evening of 24 March to 31 May 2020, which resulted in a significant reduction of primary emissions. Here, we performed the analyses of particle number size distribution measurements in the particle size range of 1.2–3 nm and 10–514 nm carried out from 15 April to 31 May 2020 (lockdown, LCD) and compared with measurements from the previous year during the same time period (15 April to 31 May 2019, business‐as‐usual, BAU) at University of Hyderabad in Hyderabad, India. The number concentrations of sub‐3 nm particles were comparable between LCD and BAU, but the number concentrations of particles greater than 10 nm diameter were lower by about 85% during LCD than BAU. It indicates that the reduction in primary anthropogenic emissions did not inhibit the formation of sub‐3 nm particles. But the frequency of occurrence of the new particle formation and growth (NPF&G) events was three‐fold lower during LCD than BAU. The ratio of formaldehyde to nitrogen dioxide indicated that India falls in a NOx‐limited regime, which reduces ambient ozone concentrations (lower condensable vapors via ozone oxidation of volatile organic compounds). Besides, the lower temperature (lower hydroxyl radical concentration) and lower wind speed during LCD may have contributed to the suppression of NPF&G events. Therefore, we emphasize the need to account for processes and interactions related to NPF&G in formulating particulate pollution mitigation policies in urban environments.

Atmospheric particle number size distribution and size-dependent formation rate and growth rate of neutral and charged new particles at a coastal site of eastern China

Coastal new particle formation (NPF) may be complicated due to the influence of both continental and marine air masses. Here we presented the result of particle number size distribution and NPF event measurements at a coastal industrial park of eastern China from 2018 to 2019. The highest nucleation-mode particle number concentration (daytime maximum: 4.9 × 103 cm−3) and NPF frequency (8% of the observation days) were observed in the continental-marine air masses that originated from North China Plain and traveled along the coastline before arriving at the coastal site. The formation rates of 2 nm particles (J2) at this coastal site are similar to those reported in the urban environments around the world, probably due to the influence of local industrial emission. Ion to total particle number concentration ratios in 2–7 nm and 7–20 nm were 1.5% and 12%, respectively, during the NPF periods. Neutral new particle formation pathway thus dominated over ion-mediated pathway at this coastal site. Our observation also showed that number concentration and formation rate of neutral new particles decreased monotonically with particle size, while those of charged new particles increased with particle size. Such difference points to additional formation and loss mechanisms of charged particles, such as ion-aerosol attachment and ion-ion recombination in the atmosphere. The behavior of appearance time-based growth rates, however, are similar for neutral and charged particles.

Characteristics of Aerosol Size Distributions and New Particle Formation Events at Delhi: An Urban Location in the Indo-Gangetic Plains

Accurate information about aerosol particle size distribution and its variation under different meteorological conditions are essential for reducing uncertainties related to aerosol-cloud-climate interaction processes. New particle formation (NPF) and the coagulation significantly affect the aerosol size distribution. Here we study the monthly and seasonal variability of aerosol particle size distribution at Delhi from December 2011 to January 2013. Analysis of aerosol particle size distribution using WRAS-GRIMM reveals that aerosol particle number concentration is highest during the post monsoon season owing to the effect of transported crop residue and biomass burning aerosols. Diurnal variations in number concentration show a bimodal pattern with two Aitken mode peaks in all the seasons. Monthly volume size distribution also shows bi-modal distribution with distinct coarse and fine modes. NPF events are observed less frequently in Delhi. Out of 222 days of WRAS data, only 17 NPF events have been observed, with higher NPF frequency during summer season. Growth rate of the nucleation mode of NPF events vary in the range 1.88–21.66 nm/h with a mean value of ∼8.45 ± 5.73 nm/h. It is found that during NPF events the Aitken and nucleation mode particles contribute more to the number concentration. Simultaneous measurement of UV flux and particulate matter (PM10and PM2.5) have also been done along with particle number size distribution measurement to understand the possible mechanisms for NPF events over the study location.

Long-term trend of new particle formation events in the Yangtze River Delta, China and its influencing factors: 7-year dataset analysis

To evaluate the influence of anthropogenic emission reductions since 2013 in China, a long-term trend analysis of the particle number size distribution (PNSD) and new particle formation (NPF) events in the Yangtze River Delta (YRD) region was conducted based on the PNSD measurement (diameter ranging from 3 to 850 nm) at the Lin'an (LAN) regional background station from 2013 to 2019. A modified Mann-Kendall test and a Theil-Sen estimator were used to calculate the overall trend of particle number concentrations in different modes and the relevant influencing factors. We observed a significant decreasing trend in the Aitken and accumulation mode number concentrations, with annual decrease rates of approximately 5.6% and 8.2%, respectively, resulting in an approximately 6.0% decline in total particles annually. However, the nucleation mode particle number concentration showed no significant trend from 2013 to 2016, but an increasing trend from 2016 to 2019, which was related to the NPF events occurrence frequency. The regional NPF events of “banana shape” accounted for an increasing fraction of all NPF events. As a key parameter influencing the NPF event, the condensation sink decreased by approximately 63% from 2013 to 2019. Moreover, the estimated sulfuric acid concentration decreased by approximately 50%, with a higher reduction rate occurring during 2013–2016 as result of the effective SO2 reduction. Surface meteorological factors (including the air temperature, relative humidity, air pressure, and wind) and the air masses origin were found to played minor roles in the long-term trend of NPF events. As PNSD and NPF events are closely related to changes in the particle emissions and regional air pollution levels, studies concerning PNSD and NPF are necessary to provide important information regarding air quality improvements and evaluating the efficacy of climate change mitigation strategies.

Performance comparison of SMPSs with soft X-ray and Kr-85 neutralizers in a humid atmosphere

Scanning mobility particle sizer (SMPS) is widely used for particle number size distribution measurements of submicron particles. In this work, two TSI® SMPSs equipped with a soft X-ray neutralizer and a Kr-85 neutralizer, respectively, were operated in parallel to measure particle number size distributions of ambient air. An independent TSI® ultrafine condensation particle counter (CPC) was used as a reference to measure the total concentration of particles in the ambient air. Our results show that the total particle concentrations measured by the two SMPSs were comparable with each other, while their size-resolved concentration ratios were size-dependent and relative humidity (RH)-dependent. Neutralizer was found to be essential to quickly bring small particles to charge equilibrium in field measurements, as indicated by the comparison of particle number size distributions measured by the Kr-85 SMPS with those inverted from naturally charged particles. The total particle concentrations measured by two SMPSs tend to exceed those by the reference CPC at high RH, hinting that the particle concentrations measured by SMPSs could be overestimated at high RH. This study urges a better understanding of the bipolar charging processes under high RH conditions.

Mathematical derivation and physical interpretation of particle size-resolved activation ratio based on particle hygroscopicity distribution: Application on global characterization of CCN activity

Size-resolved particle activation ratio (SPAR), the size-dependent ability of aerosol particles to form cloud condensation nuclei (CCN), is generally parameterized by a formula with sigmoidal shape with three key parameters. However, our understanding about the intrinsic relationship between the sigmoidal shape function and aerosol hygroscopicity distribution remains incomplete. In this study, the relationship between SPAR and particle hygroscopicity distribution is mathematically derived and relationships between key parameters for SPAR and particle hygroscopicity distribution are manifested, making it clear for the physical understanding of key CCN spectral characteristics. On the basis of the mathematically derived SPAR parameterization, a simplified method to calculate SPAR parameters (including maximum activation fraction (MAF), critical diameter and its heterogeneity of CCN-active particles) based on hygroscopicity distribution data is proposed. This simplified method is applied to Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) field measurement datasets around the world for the meta-analysis of regional and seasonal characteristics of CCN activity. It was found that, for CCN-active particles in polluted regions, the MAF can reach lower values, and the variations of both hygroscopicity and its heterogeneity can be larger, compared with those in clean regions. In summer, the MAF and the hygroscopicity of CCN can reach higher values than those in winter. In addition, the variations of SPAR parameters among different campaigns are large and thus measurements of CCN Counter or HTDMA are needed to specify the SPAR parameters at a specific site during a specific period. The bulk CCN activity at different SSs are also calculated based on the calculated SPAR by considering the measured particle number size distribution. The mathematical derivation and physical interpretation of SPAR parameterization in this study can further the understanding of CCN activity based on particle hygroscopicity distribution. The proposed simplified method to calculate SPAR parameters based on HTDMA measurements allows meta-analysis of SPAR parameters and helps expand the CCN activity datasets around the world.

Multi-year ACSM measurements at the central European research station Melpitz (Germany) – Part 1: Instrument robustness, quality assurance, and impact of upper size cutoff diameter

Abstract. The aerosol chemical speciation monitor (ACSM) is nowadays widely used to identify and quantify the main components of fine particles in ambient air. As such, its deployment at observatory platforms is fully incorporated within the European Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS). Regular intercomparisons are organized at the Aerosol Chemical Monitoring Calibration Center (ACMCC; part of the European Center for Aerosol Calibration, Paris, France) to ensure the consistency of the dataset, as well as instrumental performance and variability. However, in situ quality assurance remains a fundamental aspect of the instrument's stability. Here, we present and discuss the main outputs of long-term quality assurance efforts achieved for ACSM measurements at the research station Melpitz (Germany) since 2012 onwards. In order to validate the ACSM measurements over the years and to characterize seasonal variations, nitrate, sulfate, ammonium, organic, and particle mass concentrations were systematically compared against the collocated measurements of daily offline high-volume PM1 and PM2.5 filter samples and particle number size distribution (PNSD) measurements. Mass closure analysis was made by comparing the total particle mass (PM) concentration obtained by adding the mass concentration of equivalent black carbon (eBC) from the multi-angle absorption photometer (MAAP) to the ACSM chemical composition, to that of PM1 and PM2.5 during filter weighing, as well as to the derived mass concentration of PNSD. A combination of PM1 and PM2.5 filter samples helped identifying the critical importance of the upper size cutoff of the ACSM during such exercises. The ACSM–MAAP-derived mass concentrations systematically deviated from the PM1 mass when the mass concentration of the latter represented less than 60 % of PM2.5, which was linked to the transmission efficiency of the aerodynamic lenses of the ACSM. The best correlations are obtained for sulfate (slope =0.96; R2=0.77) and total PM (slope =1.02; R2=0.90). Although, sulfate did not exhibit a seasonal dependency, total PM mass concentration revealed a small seasonal variability linked to the increase in non-water-soluble fractions. The nitrate suffers from a loss of ammonium nitrate during filter collection, and the contribution of organo-nitrate compounds to the ACSM nitrate signal make it difficult to directly compare the two methods. The contribution of m∕z 44 (f44) to the total organic mass concentration was used to convert the ACSM organic mass (OM) to organic carbon (OC) by using a similar approach as for the aerosol mass spectrometer (AMS). The resulting estimated OCACSM was compared with the measured OCPM1 (slope =0.74; R2=0.77), indicating that the f44 signal was relatively free of interferences during this period. The PM2.5 filter samples use for the ACSM data quality might suffer from a systematic bias due to a size truncation effect as well as to the presence of chemical species that cannot be detected by the ACSM in coarse mode (e.g., sodium nitrate and sodium sulfate). This may lead to a systematic underestimation of the ACSM particle mass concentration and/or a positive artifact that artificially decreases the discrepancies between the two methods. Consequently, ACSM data validation using PM2.5 filters has to be interpreted with extreme care. The particle mass closure with the PNSD was satisfying (slope =0.77; R2=0.90 over the entire period), with a slight overestimation of the mobility particle size spectrometer (MPSS)-derived mass concentration in winter. This seasonal variability was related to a change on the PNSD and a larger contribution of the supermicrometer particles in winter. This long-term analysis between the ACSM and other collocated instruments confirms the robustness of the ACSM and its suitability for long-term measurements. Particle mass closure with the PNSD is strongly recommended to ensure the stability of the ACSM. A near-real-time mass closure procedure within the entire ACTRIS–ACSM network certainly represents an optimal quality control and assurance of both warranting the quality assurance of the ACSM measurements as well as identifying cross-instrumental biases.

Particle emissions of direct injection internal combustion engine fed with a hydrogen-rich reformate

Thermochemical Recuperation is a promising waste heat recovery method that enables utilization of the engine waste heat together with onboard hydrogen production resulting in a significant improvement in thermal efficiency and a massive reduction in gaseous pollutants emission. However, an unexpectedly high particle emission level as compared to the gasoline-fed engine was measured despite the combustion of a hydrocarbon-free hydrogen-rich methanol steam reforming (MSR) products, containing 75% mol. H2 and 25% mol. CO2. In the existing literature, this phenomenon has not described yet.In this reported study, experiments are performed to investigate reasons of the elevated particle emissions by a direct injection spark ignition engine fed with MSR reformate, and results are compared with a baseline engine fed with gasoline at the same engine loads and speeds. Results of particle number concentration and size distribution measurements show that the total particle number concentration emission of engine fed with MSR reformate is 170% higher compared to gasoline. A direct experimental comparison between the port and the direct reformate injection performed on the same engine shows an increase in particles formation with a direct injection method. Based on these findings, several hypotheses are presented attributing to excessive lubricant involvement in the combustion process. The peculiarities specific for direct reformate injection that could result to the enhanced particles formation are jet – lubricated wall interaction, lubricant vapor entrainment into the reformate jet and shorter flame quenching distance of hydrogen compared to gasoline.

Variations in submicron aerosol liquid water content and the contribution of chemical components during heavy aerosol pollution episodes in winter in Beijing.

The aerosol liquid water content (ALWC) of submicron particles (PM1) was calculated in this work by three methods based on the aerosol physical and chemical properties measurement campaigns in winter in Beijing, including (a) the PM1 volume difference between the ambient and dry states by applying the particle number size distribution and particle hygroscopicity measurement; (b) the thermodynamic equilibrium model (ISORROPIA II) based on the chemical composition; and (c) the κ-Köhler theory of chemical composition with a volume mixing scheme. The three methods agreed well with reasonable uncertainties. The ALWC showed an exponential trend depending on the relative humidity (RH), and an abundant ALWC was also favored by the high PM1 mass loading. The contribution of different chemical component to the ALWC was evaluated by the κ-Köhler method, which revealed that during the measurement, the inorganics and organics could contribute to ~80% and ~20%, respectively, under ambient RH conditions, with the largest contributor of ammonium nitrate. When the RH was above 85%, the mass concentration of ALWC was comparable to, or even larger than, that of the dry PM1.

Particle number size distribution statistics at City-Centre Urban Background, urban background, and remote stations in Greece during summer

Particle number size distribution measurements were conducted during the summer of 2012 at City-Centre Urban Background (Patras-C), Urban Background (ICE-HT in Patras, DEM in Athens, EPT in Thessaloniki), and Regional Background stations (FIN in Crete). At the City-Centre Urban Background station, the average number distribution had a geometric mean diameter peak approximately at 60 nm and the highest number concentration, whereas at the Regional Background station and the Urban Background stations it displayed a major peak approximately at 100 nm, with the Regional Background station exhibiting the lowest number concentration. The particle number size distribution at each site was divided into size fractions and, based on their diurnal variation and previous studies, we concluded that the main sources for the City-Centre Urban Background station are traffic and the regional background concentration, for the Urban Background stations fresh traffic, aged traffic, cooking and the regional background concentration, and for the Regional Background station local activities (tourism, cooking) and regional background concentration. The median number concentration that is attributed to regional background concentration for the City-Centre Urban Background, the Urban Background and the Regional Background stations are respectively 13, 29 and 45% of the total number concentration. Nucleation events were identified at DEM station, where the newly formed particles accounted for 4% of the total particle concentration for the measurement period in the size range 10–20 nm, EPT, where they accounted for 12%, and FIN, where they accounted for 1%, respectively. New Particle Formation events contribution during summer to Condensation Cloud Nuclei were therefore insignificant in the Eastern Mediterranean. Modal analysis was performed on the number distributions and the results were classified in clusters. At the City-Centre Urban Background station, the cluster-source that dominated number concentration and frequency is related to fresh and aged traffic emissions, at the Urban Background stations aged traffic emissions, while at the Regional Background station number and frequency were dominated by the regional background concentration. Based on cluster analysis, 18% of the median number distribution was due to long range transport at the City-Centre Urban Background site, 37% at the Urban Background sites, and 59% at the Regional Background site. The Flexible Particle Dispersion Model (FLEXPART) was used in order to acquire geographic origin clusters and we concluded that the Etesian flow increases the median regional background number concentration in the Mediterranean basin by a factor of 2.5–4.

Characteristics of particle emissions and their atmospheric dilution during co-combustion of coal and wood pellets in a large combined heat and power plant

Coal combustion is one of the most significant anthropogenic CO2 and air pollution sources globally. This paper studies the atmospheric emissions of a power plant fuelled with a mixture of industrial pellets (10.5%) and coal (89.5%). Based on the stack measurements, the solid particle number emission, which was dominated by sub-200 nm particles, was 3.4×1011 MJ-1 for the fuel mixture when electrostatic precipitator (ESP) was cleaning the flue gas. The emission factor was 50 mg MJ-1 for particulate mass and 11 740 ng MJ-1 for the black carbon with the ESP. In the normal operation situation of the power plant, i.e., including the flue-gas desulphurisation and fabric filters (FGD and FF), the particle number emission factor was 1.7×108 MJ-1, particulate mass emission factor 2 mg MJ-1 and black carbon emission factor 14 ng MJ-1. Transmission electron microscopy (TEM) analysis supported the particle number size distribution measurement in terms of particle size and the black carbon concentration. The TEM images of the particles showed variability of the particle sizes, morphologies and chemical compositions. The atmospheric measurements, conducted in the flue-gas plume, showed that the flue-gas dilutes closed to background concentrations in 200 sec. However, an increase in particle number concentration was observed when the flue gas aged. This increase in particle number concentration was interpret as formation of new particles in the atmosphere. In general, the study highlights the importance of detailed particle measurements when utilizing new fuels in existing power plants.Implications: CO2 emissions of energy production decrease when substituting coal with biofuels. The effects of fuels changes on particle emission characteristics have not been studied comprehensively. In this study conducted for a real-scale power plant, co-combustion of wood pellets and coal caused elevated black carbon emissions. However, it was beneficial from the total particle number and particulate mass emission point of view. Flue-gas cleaning can significantly decrease the pollutant concentrations but also changes the characteristics of emitted particles. Atmospheric measurements implicated that the new particle formation in the atmospheric flue-gas plume should be taken into account when evaluating all effects of fuel changes.” Are implication statements part of the manuscript?

Number concentrations and size distributions of nanoparticles during the use of hand tools in refurbishment activities

Hand-tools, such as sledgehammer, are widely used in refurbishment activities, nonetheless there is very little knowledge on nanoparticle generation. We measured particle number size distributions (PSD) and concentrations (PNC) in the 10-420 nm using a NanoScan Scanning Mobility Particle Sizer (SMPS) during the use of hand-tools (i.e., sanding and removal of wall) in a real indoor refurbishment environment. Results indicated that refurbishment activities from removal of wall increased average PNCs by ~6 times over the background, while was ~1.5 times higher than sanding. Highest total PNC was 1.9 × 105 particles cm30 −3, that corresponded to removal of wall activities. For sanding activities, PNC was lower as the coat of the plaster was probably slightly wet. Moreover, comparison between the two principal activities showed a similar peak in the accumulation mode (~65 nm), with a monomodal pattern. Results suggest that removal of wall activities emitted nanoparticles with a 59% of contribution in the Aitken mode. According to these data, can be inferred that the application of hand-tools in refurbishment activities generates lower total PNC than using electromechanical equipment. This study may contribute to our understanding of nanoparticle generation in refurbishment activities