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The particle number size distribution (PNSD) is crucial for evaluating air quality and mitigating environmental pollution, as particles of different sizes have diverse effects on human health and climate. However, obtaining a comprehensive understanding of PNSD is challenging due to its inherent complexities and variability. Multi-lognormal distribution models are employed to fit PNSD, as seen in climate models, but discrepancies between model fits and observed PNSD persist. This study adopts hourly data from 2017 to 2020 across eight monitoring sites in diverse environments—rural, urban, mountainous, and polar, and compares the observed PNDS with those simulated by multi-lognormal distribution models. The results demonstrated that the model generally achieved a high correlation with observed PNSD data (r2 > 0.75), effectively capturing key characteristics of nucleation and Aitken mode particles. However, the model had a tendency to overestimate the total number concentration by approximately 1.09 times, particularly noticeable under conditions of high concentrations of smaller particles. The model successfully represented prevalent bimodal size distribution patterns in urban areas with high ultrafine particle concentrations, though its performance was slightly less accurate in scenarios involving trimodal distributions. Despite these strong correlations and the model's ability to reflect diurnal and seasonal variations, which suggests its broad applicability and utility, there were notable limitations on smaller time scales and in specific particle size ranges. These limitations were particularly evident in capturing detailed phenomena relevant to new particle formation events, indicating areas where model refinement is necessary. The results highlighted the importance of investigating discrepancies between model predictions and actual observations, which is crucial for refining climate models that utilize PNDS. The uniform comparison facilitated a detailed exploration of particle properties from model results, offering deeper insights into aerosol behavior and its environmental impacts. • The multi-lognormal distribution model overestimates particle concentrations compared to actual values, by around 1.09 times. • The multi-lognormal distribution model effectively fits various particle modes and determines the particle size range. • In bimodal distributions, particle number concentrations tend to be higher, particularly for smaller particles. • The multi-lognormal distribution model exhibits high accuracy in analyzing large time scales and cyclic variations. • When dealing with finer time scales and specific particle sizes such as NPF, careful interpretation of the model's results is warranted. [ABSTRACT FROM AUTHOR]

[Display omitted] • Long-term variability of PNC at multiple schools near two airports is investigated. • With a decreasing proximity to an airfield, the PNC concentrations increases. • The road-traffic emissions are important source of PNC measured at schools. • Regional NPF had an observable influence on UFP-nf and number concentration. • After airport closure, the PNC in surrounding areas decreased by 30 %. Studies revealed airports as a prominent source of ultrafine particles (UFP), which can disperse downwind to residential areas, raising health concerns. To expand our understanding of how air traffic-related emissions influence total particle number concentration (PNC) in the airport's surrounding areas, we conduct long-term assessment of airborne particulate exposure before and after relocation of air traffic from "Otto Lilienthal" Airport (TXL) to Berlin Brandenburg Airport "Willy Brandt" (BER) in Berlin, Germany. Here, we provide insights into the spatial–temporal variability of PNC measured in 16 schools recruited for Berlin-Brandenburg Air Study (BEAR). The results show that the average PNC in Berlin was 7900 ± 7000 cm−3, consistent with other European cities. The highest median PNC was recorded in spring (6700 cm−3) and the lowest in winter (5100 cm−3). PNC showed a bi-modal increase during morning and evening hours at most measurement sites due to road-traffic emissions. A comparison between measurements at the schools and fixed monitoring sites revealed good agreement at distances up to 5 km. A noticeable decline in this agreement occurred as the distance between measurement sites increased. After TXL was closed, PNC in surrounding areas decreased by 30 %. The opposite trend was not seen after BER was re-opened after the COVID-lock-down, as the air traffic has not reached the full capacity yet. The analysis of particle number size distribution data showed that UFP number fraction exhibit seasonal variations, with higher values in spring and autumn. This can be explained by nucleation events, which notably affected PNC. The presented findings will play a pivotal role in forthcoming source attribution and epidemiological investigations, offering a holistic understanding of airports' impact on airborne pollutant levels and their health implications. The study calls for further investigations of air-traffic-related physical–chemical pollutant properties in areas found further away (> 10 km) from airports. [ABSTRACT FROM AUTHOR]

A better understanding of the particle number size distribution aids to better assess the direct and indirect effects of particles on air quality and climate. In this study, particle number concentrations (PNCs) and size distribution along with chemical components, gaseous pollutants, and meteorological parameters were measured during a cruise campaign over the Bohai Sea. Four distinct periods were identified, showing significant impacts from continental outflows and ocean emissions on the particle number size distributions. Under the strong terrestrial pollution transport period, an obvious increase of PNCs below 1 μm was observed. The significant correlation between black carbon (BC) and PNCs in the size range of 0.35–1.0 μm suggested aging of aerosols during the long-range transport. An invaded dust pollution significantly reduced PNCs below 0.5 μm, while tripled the number concentration of particles larger than 0.5 μm. The ocean moisture facilitated the mixing between dust and secondary aerosols. An intense sea fog event observed during the cruise slightly increased PNCs smaller than 1 μm while decreasing larger ones. The correlations between PNCs below 0.5 μm and BC as well as SO 2 demonstrated the impact of shipping activities on the formation of fresh particles. Aerosol vertical profiles in the marine boundary layer were measured by an unmanned aerial vehicle platform. The vertical patterns of particle number size distribution were largely governed by the origins of transported air masses and profiles of wind fields. Observations showed that the particle distribution in the lower marine boundary layer was typically inhomogeneous and rapidly evolving with time, highlighting the importance of strengthening the vertical observations of atmospheric parameters over the ocean. • Particles were measured from on a shipborne and unmanned aerial vehicle platform. • Particle number size distributions were shaped by long-range transport and meteorology. • UAV observations showed complex and fast-evolving vertical profiles of particle numbers. [ABSTRACT FROM AUTHOR]

To study atmospheric aerosols, it is essential to build networks that are continuously monitoring particle number size distribution (PNSD). PNSDs are often measured using electrical mobility spectrometers such as scanning mobility particle sizer (SMPS) which includes a neutralizer that conditions the charge state of particles to the pre-assumed distributions. During long-term atmospheric measurement, the charge state can deviate from these assumed values. Measuring both positively and negatively charged particles using a bipolar SMPS helps to capture the variations in aerosol charge state. In this study, we set up a network of bipolar SMPSs at three urban sites and three suburban sites in six Chinese cities. Removing the conventional neutralizer, the bipolar SMPS utilizes the natural aerosol charging process by atmospheric ions. Newly developed aerosol classifiers and detectors were used. Harmonized quality assurance procedures were adopted to assure the performance and the data quality, including laboratory calibrations and intercomparisons, maintenance and monitoring during field measurements, and data inversion and validation. PNSDs are effectively measured by bipolar SMPSs using natural charging process at all six sites. During six months of field measurement in these sites, ion mobility ratios fluctuate significantly while the daily averaged values are stable around 1.0. Particle number concentrations integrated from PNSDs are consistent with those directly measured by the detectors (within a variation of 10%). [Display omitted] • An atmospheric PNSD monitoring network is set up in six Chinese sites. • New instruments and QA procedures are developed and deployed in the network. • Measuring PNSD using natural charging process is verified in various environments. [ABSTRACT FROM AUTHOR]

Exposure to ultrafine particles has a significant influence on human health. In regions with large commercial airports, air traffic and ground operations can represent a potential particle source. The particle number concentration was measured in a low-traffic residential area about 7 km from Frankfurt Airport with a Condensation Particle Counter in a long-term study. In addition, the particle number size distribution was determined using a Fast Mobility Particle Sizer. The particle number concentrations showed high variations over the entire measuring period and even within a single day. A maximum 24 h-mean of 24,120 cm−3 was detected. Very high particle number concentrations were in particular measured when the wind came from the direction of the airport. In this case, the particle number size distribution showed a maximum in the particle size range between 5 and 15 nm. Particles produced by combustion in jet engines typically have this size range and a high potential to be deposited in the alveoli. During a period with high air traffic volume, significantly higher particle number concentrations could be measured than during a period with low air traffic volume, as in the COVID-19 pandemic. A large commercial airport thus has the potential to lead to a high particle number concentration even in a distant residential area. Due to the high particle number concentrations, the critical particle size, and strong concentration fluctuations, long-term measurements are essential for a realistic exposure analysis. [Display omitted] • An airport can result in high particle concentrations in a distant residential area. • The particle size distribution indicated the airport as the main source of particles. • Lower air traffic during the COVID-19 pandemic lead to lower particle concentrations. • The particle concentration showed high temporal variations. [ABSTRACT FROM AUTHOR]

Abstract In this study, a novel setup was developed to measure the vertical profile of particle number size distribution (PNSD) and meteorological parameters by using hexacopter equipped with a portable instrument package including a custom-built scanning mobility particle sizer, an optical particle counter and temperature and relative humidity (RH) sensors. By using this setup, a field experiment was carried out to investigate the vertical profiles of RH, temperature, PNSD ranged from 8 to 245 nm, and particle number concentration with the diameter ranges of 0.3–0.5 μm and 0.5–1.0 μm from the ground up to 300 m above ground level in a rural site of the North China Plain. New particle formation (NPF) event in a vertical scale was observed during the daytime cruises. The newly formed particles showed a heterogeneous vertical distribution, indicating the inhomogeneous occurrence of the NPF event vertically. During the daytime, the vertical variations in number concentration of particles larger than 0.3 μm was not obvious, while, showed a tendency to decrease associated with the increasing altitude in the evening. The newly-developed unmanned aerial vehicle research platform could be applied to study the vertical NPF events and transport processes of air pollutants within the atmospheric boundary layer and urban canopy, and to monitor source emissions with the purpose of environment management. Graphical abstract Unlabelled Image Highlights • A hexacopter research platform was developed to measure aerosol vertical profiles. • The portable aerosol instruments are robust and reliable devices, which can be used in UAV. • The vertically inhomogeneous new particle formation event was observed over NCP. [ABSTRACT FROM AUTHOR]

Abstract This work reports the first statistical analysis of multi-annual data on tropospheric aerosols from the German Ultrafine Aerosol Network (GUAN). Compared to other networks worldwide, GUAN with 17 measurement locations has the most sites equipped with particle number size distribution (PNSD) and equivalent black carbon (eBC) instruments and the most site categories in Germany ranging from city street/roadside to High Alpine. As we know, the variations of eBC and particle number concentration (PNC) are influenced by several factors such as source, transformation, transport and deposition. The dominant controlling factor for different pollutant parameters might be varied, leading to the different spatio-temporal variations among the measured parameters. Currently, a study of spatio-temporal variations of PNSD and eBC considering the influences of both site categories and spatial scale is still missing. Based on the multi-site dataset of GUAN, the goal of this study is to investigate how pollutant parameters may interfere with spatial characteristics and site categories. Highlights • Pollutant parameters show various connections with spatial scale and site category. • Lower spatial correlation of PNC and eBC is observed for lager spatial distance. • eBC connects sites with similar influence of anthropogenic sources. • N [10-30] are mainly driven by local source. • N [200-800] connects sites located at same geographical area. [ABSTRACT FROM AUTHOR]

Abstract The ice nucleating particles (INPs) in the ambient air in Beijing during the spring of 2017 were observed using an improved 5-L version of Bigg's mixing cloud chamber. The characteristics of the diurnal INPs concentrations are analyzed and compared with measurements made in 1963, 1995 and 1996. The particle number size distribution was also measured simultaneously. The correlation between the concentration of INPs and the aerosol number concentration in different size ranges is discussed. Moreover, the relationship between the concentration of INPs and different meteorological factors, such as wind speed, air pressure, temperature, humidity and weather conditions, are analyzed. From the results of observation, in general, the concentrations of INPs at −20 °C, −25 °C and −30 °C temperatures trend with each other on a day to day basis, although there are slight differences in some cases at −20 °C. As the activation temperatures decrease by 5 °C, the concentration of INPs increases by about one order of magnitude. The concentration of INPs increases significantly when air pollution is severe, but the specific relationship between INPs and pollution needed to be verified in the follow-up work, which is related to the source of pollution and the aerosol components. Compared with historical experimental data, interpreting trends using short sampling periods in individual years over decadal time frames, the average concentrations of INPs in Beijing increased by approximately 15 times from 1963 to 1996, but in the past 20 years, the concentration of INPs has decreased significantly. For aerosols with particle size that exceeds 0.5 μm, the correlation coefficient between aerosol number concentration and INPs increases significantly with increasing aerosol particle size; however, it tends to stabilize at approximately 0.6 for aerosol particles larger than approximately 2 μm. A comparison with meteorological parameters shows that the concentration of INPs is inversely correlated with wind speed, and displays a positive correlation with relative humidity. These results indicate that conditions that favor dispersion lead to reduced concentrations of INPs. Highlights • Observe ice nucleating particles in Beijing using an improved Bigg's mixing cloud chamber. • Compare ice nucleating particles with particle number size distribution. • Analyze the relationship between ice nucleating particles with pollution. • Comparison with historical, analyze the changes of ice nucleating particles in Beijing. [ABSTRACT FROM AUTHOR]

The present study is based on hourly aerosol particle and ancillary data taken at three stations in Northeastern Germany 150–200 km apart in the years 2009 through 2015 in order to investigate systematic process related differences that might show up when connecting their data with forward and backward air mass trajectories. The analysis of changes in the atmospheric aerosol during air mass transport between the stations focused on two low-pollution-to-high-pollution pathways of similar distance around 200 km. Despite rather different initial size distributions the increases in total concentration of particle number, volume, and black carbon agreed within 15%. Systematic variations were found in the different concentration increases as a function of time of day at which an interstation air mass transport took place that could be explained with related source and transport processes. With Radar-based precipitation data at the stations and along connecting trajectories sub-cloud particle scavenging was investigated. At each station sub-cloud particle scavenging coefficients were determined as a function of particle size between 10 and 700 nm diameter, and as a function of precipitation sums. Median particle scavenging coefficients taken over the central part of the size range of the study strongly increased between 0.2 and 1 mm of precipitation and then planed out towards higher precipitation values. With the particle scavenging coefficients determined at the individual stations and precipitation data along connecting trajectories the sub-cloud particle scavenging analysis was extended to wet scavenging along the transport paths yielding median sub-cloud scavenging ratios over the range 0.2–25 mm of precipitation sums with a non-linear shape similar to that of the median particle scavenging coefficients at the individual stations. Whereas in light precipitation more than 80% of the initial particles in the considered range survived 150–200 km of transport, more than 50% was scavenged by more than 15 mm of precipitation during aerosol transport. [ABSTRACT FROM AUTHOR]

This study synthesizes for the first time results from simultaneous aerosol measurements performed at seven diverse locations distributed all over the Spanish geography. The observations were carried out during two field campaigns in 2012–2013, one-month each and during different seasons. These field campaigns were performed in the framework of the Spanish Network of DMAs (REDMAAS) activities. Measurement sites were grouped as polluted sites (urban background) and clean sites (rural background and high-altitude sites). Seasonal differences were more important at polluted sites, mainly related to meteorology and aerosol sources. Higher total particle concentrations were found during the cold period, driven mainly by Aitken-mode particles (traffic-related aerosol particles). In clean sites, particle concentrations were higher during the warm period. Mild meteorological conditions in combination with the absence of local sources during the cold period make atmospheric nucleation an important contributor to ultrafine particles. These results are reflected in aerosol dynamical processes. Ultrafine particle bursts were frequent in both periods at the clean sites and in the warm period at most polluted sites. Shrinkages processes were identified at three sites (two polluted and one clean site) during the warm period. Meteorology (wind speed and solar radiation) and a highly-volatile aerosol (formed from atmospheric nucleation or traffic emissions) explain this behaviour. Ultrafine particles exhibited a different behaviour at inland and coastal sites. The highest total particle concentrations were observed at coastal sites during the warm period. At these sites, the smallest particle modal diameters and the highest variations of particle number size distributions in the smaller particle size range were also found, particularly in the warm period. This may be the result of the high diffusion conditions and mixing of different air masses (clean and polluted) caused by sea-land breezes. Our findings can be explained by the local and regional characteristics of each site, such as meteorology and aerosol sources (types, proximity …) and the influence of meteorology on atmospheric transformation processes. [ABSTRACT FROM AUTHOR]

Particle number size distribution in a suburban Beijing was measured during the HOPE-J3A (Haze Observation Project Especially for Jing–Jin–Ji Area) field campaigns in 2015 from 18 June to 23 July (summer) and 2 to 25 December (winter). Average particle concentrations during the summer and winter campaigns were 9.6 ± 4.8 × 10 3 cm −3 and 13.9 ± 8.3 × 10 3 cm −3 , respectively. Particle numbers were dominated by Aitken mode particles in both seasons. During the winter campaign, pollution events occurred every four to five days, each lasting for two to three days. In contrast, pollution events lasted for one to two days every six to seven days during the summer campaign. Aitken mode particles were 50% higher in the winter but new particle formation (NPF) events occurred more frequently in the summer. NPF events usually starts at around 10:00 LT (local time) in the summer but 12:00 LT in the winter. Aitken and accumulation mode particles accounted for 43.5% and 38.2% of all particles. The proportion of Aitken mode to total particles remained almost the same during summer, while it increased as haze intensified in winter. Particle number concentration was closely correlated with traffic and residents living activities and wind speed, with higher concentrations during rush hours, heating period and in the southerly wind. These results, when combined with trajectory cluster analysis, suggest that Aitken and accumulation mode particles were mainly from regional transport during the summer campaign, but from vehicle and coal-combustion emissions during the winter campaign. [ABSTRACT FROM AUTHOR]

Simultaneous particle number size distribution measurements were performed in the urban environment of Budapest, Vienna, and Prague, three Central European cities located within 450 km of each other. The measurement days from the continuous, 2-year long campaign were classified for new particle formation (NPF) events using an adapted classification scheme for urban sites. The total numbers of NPF event days were 152 for Budapest, 69 for Vienna, and 143 for Prague. There were 12 days when new particle formation took place at all three sites; 11 out of these 12 days were in spring and in summer. There were only 2 (Budapest-Vienna), 19 (Budapest-Prague), and 19 (Vienna-Prague) nucleation days, when NPF did not occur on the third site. The main difference was related to source and sink terms of gas-phase sulphuric acid. Air mass origin and back-trajectories did not show any substantial influence on the atmospheric nucleation phenomena. The relative contribution of particles from NPF with respect to regional aerosol to the particles originating from all sources was expressed as nucleation strength factor. The overall mean nucleation strength factors were 1.58, 1.54, and 2.01 for Budapest, Vienna, and Prague, respectively, and showed diurnal and seasonal variations. The monthly mean NSF varied from 1.2 to 3.2 in Budapest, from 0.7 to 1.9 in Vienna, and from 1.0 to 2.3 in Prague. This implies that the new particle formation in cities is a significant source of ultrafine (UF) particles, and the amount of them is comparable to the directly emitted UF particles. [ABSTRACT FROM AUTHOR]

Exhaust particle emissions from a heavy duty diesel engine using B20 biodiesel (20% biodiesel blend with 80% diesel by volume) were investigated, and the engine was equipped with three kinds of exhaust aftertreatment devices: DOC (diesel oxidation catalyst), DOC + DPF (diesel particle filter), and DOC + CDPF (catalyzed diesel particle filter). Particle mass, particle number and size distribution, and PAHs (polycyclic aromatic hydrocarbons) and inorganic ions in the particle emissions from the engine were studied. Compared with the engine without exhaust aftertreatments, DOC decreased nucleation mode particle number by 19.83%, while accumulation mode particles exhibited slight changes. The DOC + DPF reduced the total particle number by 82.54%, while the DOC + CDPF reduced it by 91.71%. Compared with the engine without exhaust aftertreatments, the three aftertreatments were shown to reduce total PAH emissions. DOC + DPF and DOC + CDPF can decrease total TEQ (toxicity equivalent quantity) effectively with a sharp decrease in PAH mass. The DOC increased the TEQ of particles by 46.9%. The catalyst in the DOC increased some high molecular weight PAHs such as BaA, BbF + BkF, and BaP, which led to the increase in TEQ. The DOC increased the total inorganic ions by 2%, while the DOC + DPF and DOC + CDPF decreased inorganic ions by 89.5% and 82.9%, respectively. Catalysts in DOC and CDPF promotes the formation of SO 4 2− and NO 3 − , which leads to higher inorganic ion emissions with DOC than no aftertreatments and higher inorganic ion emissions with a DOC + CDPF than with a DOC + DPF. [ABSTRACT FROM AUTHOR]

In this study, a three-dimensional air quality model with detailed aerosol microphysics (NAQPMS + APM) was applied to simulate the fine particle number size distribution and to explain the spatiotemporal variation of fine particle number concentrations in different size ranges over Beijing and surrounding areas in the haze season (Jan 15 to Feb 13 in 2006). Comparison between observations and the simulation indicates that the model is able to reproduce the main features of the particle number size distribution. The high number concentration of total particles, up to 26600 cm −3 in observations and 39800 cm −3 in the simulation, indicates the severity of pollution in Beijing. We find that primary particles with secondary species coating and secondary particles together control the particle number size distribution. Secondary particles dominate particle number concentration in the nucleation mode. Primary and secondary particles together determine the temporal evolution and spatial pattern of particle number concentration in the Aitken mode. Primary particles dominate particle number concentration in the accumulation mode. Over Beijing and surrounding areas, secondary particles contribute at least 80% of particle number concentration in the nucleation mode but only 10–20% in the accumulation mode. Nucleation mode particles and accumulation mode particles are anti-phased with each other. Nucleation or primary emissions alone could not explain the formation of the particle number size distribution in Beijing. Nucleation has larger effects on ultrafine particles while primary particles emissions are efficient in producing large particles in the accumulation mode. Reduction in primary particle emissions does not always lead to a decrease in the number concentration of ultrafine particles. Measures to reduce fine particle pollution in terms of particle number concentration may be different from those addressing particle mass concentration. [ABSTRACT FROM AUTHOR]

Aerosol number size distributions, PM mass concentrations, alveolar deposited surface areas (ADSAs) and VOC concentrations were measured in a model room when aerosol was emitted by sources frequently encountered in indoor environments. Both combustion and non-combustion sources were considered. The most intense aerosol emission occurred when combustion sources were active (as high as 4.1 × 10 7 particles cm − 3 for two meat grilling sessions; the first with exhaust ventilation, the second without). An intense spike generation of nucleation particles occurred when appliances equipped with brush electric motors were operating (as high as 10 6 particles cm − 3 on switching on an electric drill). Average UFP increments over the background value were highest for electric appliances (5–12%) and lowest for combustion sources (as low as − 24% for tobacco cigarette smoke). In contrast, average increments in ADSA were highest for combustion sources (as high as 3.2 × 10 3 μm 2 cm − 3 for meat grilling without exhaust ventilation) and lowest for electric appliances (20–90 μm 2 cm − 3 ). The health relevance of such particles is associated to their ability to penetrate cellular structures and elicit inflammatory effects mediated through oxidative stress in a way dependent on their surface area. The highest VOC concentrations were measured (PID probe) for cigarette smoke (8 ppm) and spray air freshener (10 ppm). The highest PM mass concentration (PM 1 ) was measured for citronella candle burning (as high as 7.6 mg m − 3 ). [ABSTRACT FROM AUTHOR]

Fossil fuel combustion should be decreased in future years in order to lower the CO 2 emissions of energy production. The reduction can be achieved by increasing the amount of CO 2 -neutral fuels in energy production. Here 6–13% of coal was substituted with industrial or roasted pellets in a pulverized fuel-fired power plant without making any changes to fuel grinding or low-NO x burners. The effect of pellet addition for the flue gas particles was studied with direct sampling from the boiler super heater area. Based on primary dilution ratio tests, transmission electron microscope images, and the natural electric charge of the particles, it was observed that particles in the flue gas are spherical and have been formed in the boiler at high temperatures. The pellet addition lowered the total particle number concentrations with all of the studied pellet–coal mixtures in comparison to the coal combustion. The 10.5% industrial pellet addition caused a second mode in the particle number size distribution. In addition, based on the chemical analysis of the collected size-fractioned particle samples, results indicated that the pellet addition did not increase the corrosion risk of the boiler. However, the changes in the particle number size distribution and total particle number concentration can affect the operation of electrostatic precipitators and flue gas cleaning. [ABSTRACT FROM AUTHOR]

Temporary strict emission control strategies were conducted to ensure good air quality for China's V-Day parade (August 20–September 3, 2015) in Beijing and nearby cities. The influence of the emission control on particle number size distribution (PNSD) was evaluated based on the long-term measurements of PNSD at a rural site (Shangdianzi) located northeast of Beijing. This study also presented the comparison results of PNSD during the parade in 2015 and the Olympics in 2008 (August 8–23), as well as the same period without strict emission control in 2010–2013 (August 20–September 3). Compared with the same period in 2010–2013 and 2008 Olympics, the accumulation mode particle number concentration showed a significant reduction in 2015, and the PM 1 mass concentration decreased by approximately 60–90%. The alleviation of the PM 1 was also associated with the weather conditions. The back trajectories analysis results showed that the southerly air mass passing through the polluted areas accounted for 14% of the total back trajectories in 2015, which contributed to approximately 60% in the other years. During the control period in 2015, there were six new particle formation (NPF) events observed, with a higher frequency, but a lower formation rate and growth rate than the same period in 2010–2013. The comparison of the condensation sink ( CS ), sulfuric acid, solar radiation and relative humidity among the different years indicated that at Shangdianzi station, the first factor in determining the NPF occurrence was the CS , and the second factor could be the concentration level of precursor vapors participating in the NPF event (e.g., sulfuric acid). [ABSTRACT FROM AUTHOR]

To characterize the features of particle pollution, continuous measurements of particle number size distributions and chemical compositions were performed at an urban site in Beijing in January 2013. The particle number and volume concentration from 14 nm to 1000 nm were (37.4 ± 15.3) × 10 3 cm − 3 and (85.2 ± 65.6) μm 3 cm − 3 , respectively. N-Ait (Aitken mode) particles dominated the number concentration, whereas N-Acc (accumulation mode) particles dominated the volume concentration. Submicron particles were generally characterized by a high content of organics and SO 4 2 − , and a low level of NO 3 − and Cl − . Two types of pollution episodes were observed, characterized by the “explosive growth” (EXP) and “sustained growth” (SUS) of PM 2.5 . Fine particles greater than 100 nm dominated the volume concentration during the ends of these pollution episodes, shifting the maximum of the number size distribution from 60 nm to greater than 100 nm in a few hours (EXP) or a few days (SUS). Secondary transformation is the main reason for the pollution episodes; SO 4 2 − , NO 3 − and NH 4 + (SNA) accounted for approximately 42% (EXP) and greater than 60% (SUS) of the N-Acc particle mass increase. The size distributions of particulate organics and SNA varied on timescales of hours to days, the characteristics of which changed from bimodal to unimodal during the evolution of haze episodes. The accumulation mode (peaking at approximately 500–700 nm) was dominated by organics that appeared to be internally mixed with nitrate or sulfate. The sulfate was most likely formed via heterogeneous reactions, because the SOR was constant under dry conditions (RH < 50%) and began to increase when RH > 50%, suggesting an important contribution from heterogeneous reactions with abundant aerosol water under wet conditions. Finally, the correlations between [NO 3 − ]/[SO 4 2 − ] and [NH 4 + ]/[SO 4 2 − ] suggest that the homogenous reaction between HNO 3 and NH 3 dominated the formation of nitrate under conditions of lower aerosol acidity. Therefore, controlling the precursors of SNA will effectively help to reduce the fine particulate pollution during winter in Beijing. [ABSTRACT FROM AUTHOR]

The variation of ambient relative humidity (RH) affects the water uptake of aerosols in the atmosphere, thereby altering the aerosol size distribution and mass concentration. In this study, aerosol size distributions under both dry and ambient RH conditions are measured using an active RH-controlled dry-ambient aerosol size spectrometer (DAASS) at an urban site in Beijing during the springtime of 2021, and the aerosol liquid water content (ALWC) is derived accordingly. During the measurement period, a sharp increase of the ALWC was commonly observed when ambient RHs reached above 50%, demonstrating a potential phase change of the aerosol which further increases the rate of water uptake. Considerably high ALWC events were observed during the nighttime, with further elevated ambient RH above 60%. The liquid water accounts for up to 42.5% of the total aerosol volume, corresponding to a maximum ALWC of 8.79 μg m−3. The evolution of geometric mean diameter of accumulation mode particles agrees well with the enhancement of the ALWC (R2 of 0.73), revealing a significant growth of accumulation mode particles resulting from water uptake. Besides, by investigating the RH-dependent ambient aerosol surface area concentration, it is found that the aerosol surface area concentration can be underestimated by ∼20% under dry conditions when the ambient RH elevates to above 70%. • Sharp increases of the ALWC were observed under ambient RHs above 50% during the nighttime. • The aerosol water uptakes are represented by a significant growth of accumulation mode particles. • The aerosol surface area concentration can be underestimated under dry conditions when the ambient RH elevates to above 70%. [ABSTRACT FROM AUTHOR]

Particle size, composition and optical properties were measured at a regional atmosphere background station in the Yangtze River Delta (YRD) to understand the formation and evolution of haze-fog episodes in Jan. 2013. The peak of particle number size distribution was in the size range of 80–100 nm during the measurements. PM 1 mass concentration contributed 84% to the total particle mass (PM 10 ). Based on visibility and ambient relative humidity, three types of weather conditions (i.e., clear, haze and fog) were classified in this study. The extinction coefficients of PM 1 and PM 10 under dry conditions were simulated by the Mie model. Under dry conditions, PM 1 was found to contribute approximately 91% to the light extinction coefficient of PM 10 . However, the PM 1 with the assumption of dry state was found to contribute approximately 85% to the ambient extinction coefficient of PM 10 during clear conditions, 58% during haze conditions and approximately 41% during fog conditions. The variation of the dry PM 1 contribution was related to the water uptake of particles under different relative humidity conditions. A severe haze-fog event on Jan. 14–17 was discussed in more detail as a case study. Two episodes were chosen to show that nitrate and organics dominated the aerosol component during the severe haze-fog episode and were related to secondary aerosol formation and air mass origin. Nitrate played a more dominant role than sulfate in heavy haze formation in the YRD region, which was different from the North China Plain region. [ABSTRACT FROM AUTHOR]

Particle number size distributions in a mobility diameter range of 6–1000 nm and size-resolved number concentrations were determined with a time resolution of 10 min for a near-city background, city centre, street canyon and road tunnel environments in Budapest. Median N 6–100 concentrations for the sites listed were 3.1 × 103, 9.3 × 103, 19.4 × 103 and 123 × 103 cm−3, respectively. Contributions of the ultrafine (UF) particles (<100 nm) to the total particle number for all locations were rather large (up to 86%), and do not seem to vary substantially in time. Diurnal variations of the mean N 6–100 concentrations had different patterns for both the various urban sites, and for workdays and weekends. Nucleation strength factor (NSF) was introduced for the first time to quantify the relative importance of new particle formation with respect to all sources of UF particles. During the daytime in summer, nucleation in the near-city background was a major production process of UF particles with a daily mean relative contribution of 42%. In the city centre and street canyon, the daily mean relative contributions of nucleation to the UF particles were 30% and 23%, respectively. Median particle diameters for the background, city centre, street canyon and road tunnel environments were 61, 42, 35 and 42 nm, respectively, so they were jointly influenced with the anthropogenic impact and aerosol ageing. Monthly mean frequency of new particle formation and growth events in the background seems somewhat larger, while it appears smaller for the street canyon in comparison to the city centre. [ABSTRACT FROM AUTHOR]

Abstract: Fine and ultrafine particles affect human health, especially in urban areas with a large number of emission sources and significant particle number concentrations. The mixture of different aerosol sources, their temporal evolution over the diurnal course and the impact of naturally occurring processes, e.g. particle nucleation, all contribute to the spatio-temporal exposure variability across a city and its suburban areas. A differentiation between different aerosol source types is of importance for the assessment of urban aerosol pollution and exposure in a city at a certain point in time. Therefore three years of particle number size distribution (NSD) measurements from three European cities were analysed by using cluster analysis in order to identify characteristic size distributions (signatures) which are associated to specific meteorological and spatio-temporal properties. A ‘triple-site’ approach was established with data from roadside, urban background and rural sites measured over a diameter size range of 8 < D p < 700 nm. After applying two different clustering approaches – a ‘regression guided’ and an ‘observational’ K-Means clustering – a number of 7 clusters were best representing the occurring individual aerosol “signature types”: two ‘low pollution’ clusters that showed the highest relative occurrence of around 40% on average, an ‘aged combustion’ type (∼20%), a ‘traffic’ (∼13%), a ‘remote transport’ cluster (∼10%), a cluster consisting of various unspecified local emission sources (∼10%) and a ‘particle formation’ cluster (∼7%). The cluster size distributions were distinguishable by their total number concentration, peak mode diameters and shape of the size distribution. A specific signature was assigned to each of these cluster types based on the temporal and seasonal occurrence and the prevailing meteorological conditions. The ‘regression guided’ approach was able to slightly better differentiate between homogeneous data whereas the weakness mainly lies in the time-intensive data preparation. [Copyright &y& Elsevier]

Particle microphysical and chemical properties, including particle number size distribution (PNSD) and chemical composition of both ambient PM 1 and PM 10 particles were measured in the North China Plain (NCP) during the Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) campaign in November 2018. Focused on the differences of measured PNSD between PM 1 and PM 10 , the variations of aerosol microphysical and chemical properties in fog were analyzed and their corresponding influence on fog droplets evolution was evaluated. Two nighttime fog events were observed on the 12th and 13th November, respectively. During fog events, PNSDs of particles with diameter larger than ∼200 nm sampled from the PM 10 inlet were similar to those after fogs. But in particle size range larger than 200 nm, particles number concentration sampled from the PM 1 inlet were very few and much lower than those after fogs, indicating that some particles larger than 200 nm have grown into droplets with diameter larger than 1 μm and thus were not detected under the PM 1 inlet. No significant decrease in particle number concentration larger than ∼200 nm was detected under the PM 10 inlet after the dissipation of these fog events, suggesting that fog droplets were generally smaller than 10 μm and could be sampled by the PM 10 inlet. The additional particles sampled in PM 10 in fogs demonstrated a normal distribution, which indicates that they belonged to an individual particle group externally mixed with those sampled under the PM 1 impactor and could outgrow 1 μm either through hygroscopic growth or through activation. This can lead to uncertainties in droplet number concentration estimations within fog from microphysical and chemical properties measurements of the aerosol with assumption of fully internal mixture. We find that PM 1 hygroscopicity derived from particle chemical composition measurements was overestimated, which may result in significant bias in the estimated droplets number concentration in the North China Plain. These results and approaches in this study can improve the understanding of aerosol microphysical properties in fogs and the corresponding influence of aerosol particles on fog microphysics. [Display omitted] • Simultaneous measurements of PM1 and PM10 during fog events in the North China Plain. • Differences between PNSDs of PM1 and PM10 suggest additional particles in PM10 different from PM1. • Ignoring external mixing state of PM10 leads to an overestimated droplet number concentration. [ABSTRACT FROM AUTHOR]

Abstract: Three years of aerosol measurements from four European cities were analysed to identify and quantify the parameters influencing the particle number size distribution (NSD) at different measurement sites (Copenhagen, Helsinki, Leipzig, London). A ‘triple-site’ approach was established with data from a roadside, an urban background and a rural measurement station, which was available for each city. The NSD measurements were conducted over a diameter size range of 8–700 nm. The average annual total number concentrations varied between 1700 cm−3 (Finnish rural site) and 23,000 particles cm−³ (London roadside). Highest variability on the diurnal course was found for the roadside sites and on the seasonal course for the rural sites. A first identification of the influencing parameters was found using correlation analysis. The most dominating factors were then quantified using a multiple linear regression approach documenting the highest influence for daytime (45%) followed by wind direction (18%), season (12%), wind speed (11%), temperature (8%) and solar radiation (6%), on average. The variation of influence between the different cities is analysed and discussed. Subsequently NSDs were modelled using the regression approach in order to verify how well the parameters are capable of ‘explaining’ the actual NSD, showing best performance for roadside NSD with correlation coefficients between 0.65 and 0.8 and limited performance for the rural sites (0.5–0.6). [Copyright &y& Elsevier]

We developed a simple model to calculate the regional deposited dose of submicron aerosol particles in the respiratory system. This model incorporates measured outdoor and modeled indoor particle number size distributions, detailed activity patterns of three age groups (teens, adults, and the elderly), semi-empirical estimation of the regional deposition fraction, hygroscopic properties of urban aerosols, and reported breathing minute volumes. We calculated the total and regional deposited dose based on three concentration metrics: particle number (PN), mass (PM), and surface area (PSA). The 24-h total deposited dose of fine particles in adult males was around 40μg (57×109particles, 8×102mm2) and 41μg (40×109particles, 8×102mm2) on workdays and weekends, respectively. The total and regional 24-h deposited dose based on any of the metrics was at most 1.5 times higher in males than in females. The deposited dose values in the other age groups were slightly different than in adults. Regardless of the particle size fraction or the deposited dose metric, the pulmonary/alveolar region received the largest fraction of the deposited dose. These values represent the lowest estimate of the deposited dose and they are expected to be higher in real-life conditions after considering indoor sources of aerosol particles and spatial variability of outdoor aerosols. This model can be extended to youngsters (<12years old) after gaining accurate information about the deposition fraction inside their respiratory system and their breathing pattern. This investigation is foreseen to bridge the gap between exposure and response in epidemiological studies. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of airborne particle number size distributions, particle number and PM2.5 concentrations were conducted at two bus stations of different designs: open station and canyon station, operated according to the same timetables and fleet compositions, as well as at a reference point in Brisbane, Australia. Simultaneous traffic and meteorological parameters were also monitored, aiming to quantify particle characteristics and investigate the impact of station design and meteorological conditions on particle emissions at the two bus stations. It was found that there was no significant difference in average particle number concentrations in the size range 7–3000nm (PN7–3000) between the two stations (fine days: p =0.90 and rainy days: p =0.80), and that PN50–120 contributed to the largest proportion of particle number concentrations. PN20–30 were observed to increase at the open station during all time periods, except 0:00–7:00, which is likely to be attributed to the lower average daily temperature at the open station (around 7°C lower than at the canyon station). During precipitation, it was found that particle number concentration in the size range 25–250nm decreased greatly, and the average daily reduction in PM2.5 concentration on rainy days compared to fine days was 44.2% and 22.6% at the open and canyon station, respectively. The effect of ambient wind speeds on particle number concentration was also examined, and no relationship was found between particle number concentration and wind speed for the entire measurement period. In addition, 33 pairs of average half-hourly PN7–3000 concentrations were calculated and identified at the two stations, during the same time of a day, and with the same ambient wind speeds and precipitation conditions. The results of a paired t-test showed that the average half-hourly PN7–3000 concentrations at the two stations were not significantly different at the 5% confidence level (t =0.06, p =0.96), which indicates that the different station designs were not a crucial factor for influencing PN7–3000 concentrations. This finding implies that the timescale of dispersion at the bus stations was comparatively long, and that the source contribution was more important compared to the atmospheric dispersions associated with different station designs. [Copyright &y& Elsevier]

Two-year measurements of particle number size distribution (3nm–10μm) were conducted in Beijing, China since March 2004. Their seasonal, weekly and diurnal variations and dependencies on meteorological parameters were investigated. The annual average particle number concentrations of the nucleation mode (3–20nm), Aitken mode (20–100nm), and accumulation mode (0.1–1μm) are 9000cm−3, 15,900cm−3, and 7800cm−3, respectively. Particle number concentrations in Beijing are generally higher than that in cities of developed countries, especially for the accumulation mode particles. Both the highest total particle number concentration and the lowest volume concentration occurred in spring due to the frequent nucleation events. However, the minimum particle number concentration was observed in summer, and the maximum volume concentration in fall. The diurnal variation of the nucleation mode particles was mainly influenced by nucleation events, primarily in spring and winter. The diurnal variation of number concentration of the Aitken mode particles closely correlates with the traffic densities in all the four seasons. At the same time, obvious contribution of the growth of the nucleation mode to the number concentration of the Aitken mode particle has been also found in spring, summer, and fall. Significant differences in diurnal patterns of particle number concentrations between workdays and weekends are not observed in Beijing. Local wind speed plays an important role in shaping the particle number size distributions in the urban area of Beijing. With increasing wind speed, the nucleation and coarse mode particle number concentrations increase, while the number concentrations of the Aitken mode and accumulation mode particles decrease. A “U-shape relationship” between the total particle volume concentration and wind speed is observed. Frequently low wind speed (lower than 3m s−1) in Beijing is one of key factors leading to the poor air quality and low visibility. [Copyright &y& Elsevier]

Abstract: Characterization and emission rates of indoor aerosols have been of great interest. However, few studies have presented quantitative determinations of aerosol particle emissions during indoor activities. In the current study we presented and investigated the physical characteristics and size-fractionated emission rates of indoor aerosol particles during different activities in a house (naturally ventilated) located in Prague, Czech Republic. We utilized a multi-compartment and size-resolved indoor aerosol model (MC-SIAM) to investigate the indoor-to-outdoor relationship of aerosol particles and also to estimate their emission rates. When the windows and the main door were closed for several hours and there were minor indoor activities that did not produce significant amounts of aerosol particles, the particle number concentration showed similar levels at different indoor locations. As expected, the natural ventilation did not provide a controlled indoor-to-outdoor relationship of aerosol particles. As previous studies have emphasized, cooking and tobacco smoking activities are major sources indoors; the total particle number concentration was, respectively, as high as 1.8×105 and 3.6×104 cm−3 with emission rates around 380 and 36cm−3 s−1. During intensive cooking activities the outdoor aerosol particle concentrations were also affected even though windows were closed. It seems that a simple model is not able to describe the fate of indoor aerosols within a multi-compartment construction; instead, a numerical and dynamic model with a multi-compartment approach is needed. Based on the indoor aerosol model simulations, the deposition rate was comparable to previous studies with friction velocity between 10–30cms−1 and surface area to volume ratio around 2.9–3.1m−1. The penetration factor was equivalent to G3 filter standards and the ventilation rate varied between 0.6–1.2h−1. Based on the emission rate analysis, aerosol particles produced during tobacco smoking and incense stick burning remain airborne for a longer time than cooking particles. It seems that aerosol particles emitted during tobacco smoking and incense stick burning undergo different processes; therefore, there is a need for a combined physical–chemical indoor aerosol model to better describe the evolution of indoor aerosol particles due to different activities. [Copyright &y& Elsevier]

Abstract: In May 2001, the large-scale field project BAB II was performed at the highly frequented motorway BAB (Bundesautobahn) A656 with two traffic lanes in each direction between the German cities Heidelberg and Mannheim. Extensive measurements of air pollutants were carried out on both sides of the motorway. In a distance of 60m (north side) and 84m (south side) to the traffic lanes, two 52-m-high towers were installed, at which electrically powered elevators were fixed. In these elevators, two NO x analysers, an Electrical Low Pressure Impactor (ELPI; measurement of the particle number size distribution in the diameter range between 30nm and 10μm) and a Diffusion Charger (DC; measuring the particle surface area concentration), were operated to record continuous vertical profiles from 5 to 50m above the earth''s surface. On the upwind side, particle number and surface area concentration as well as NO x values were constant over the entire height profile. On the downwind side, increased concentrations appeared in the near-ground range: in the forenoon, a monotonous decrease in pollutant concentrations with increasing height was found, while around noon the concentration maximum of the particles was slightly shifted to 10m above ground. This height dependence was found for two different size ranges, i.e., for particles with (consisting of soot particles and nucleation mode particles formed by condensation as a result of cooling of the exhaust gas after emission), and for coarse particles (, abrasion and resuspension products). In the size range between 300 and 700nm, no height dependence was found, corroborating the fact that motor traffic emits only few particles in this size range. On the downwind side of the motorway, only background concentrations were measured above 25m. The results of the profile measurements were confirmed by stationary measurements of particle size distributions with Scanning Mobility Particle Sizers (SMPS) at various heights. A good correlation between particle surface area and NO x concentration was observed. Vehicle emission factors were determined for the particle surface area, number and volume of several size ranges. [Copyright &y& Elsevier]

Abstract: The concentration and size distribution of atmospheric particles were traced upwind, inside and downwind a hill cap cloud within the ground-based cloud passage experiment FEBUKO, which was carried out at the mountain ridge Thüringer Wald (Germany) during October 2001 and 2002. Three cloud events were examined in detail for which the connected flow between all three sites was meteorologically confirmed and the influence of entrainment and local sources on particle concentration and size distribution was only of minor importance. Modifications of the number size distributions between 60 and 300nm particle diameter that are attributed to cloud processing were observed comparing upwind and downwind dry particle size distributions. Despite a small interference of droplet deposition, a maximum in-cloud mass production of 0.38μgm−3 was found accounting for 5% of the upwind aerosol mass. The corresponding mass production rate was estimated to 1.16μgm−3 h−1. A formation of new ultra-fine particles was detected in the outflow of the orographic clouds during nighttime yielding number concentrations up to 300cm−3 at a pre-existing dry particle surface area of about 300μm2 cm−3. At a more than twice as high particle surface area, i.e. when adsorption of condensable gases on existing particles became more important, no new particle formation was observed. Whereas the in-cloud mass production proceeded rather continuously throughout the cloud events, the particle production occurred during periods of 15min up to 2h within the cloud events. In the absence of actinic radiation, ternary nucleation of gaseous substances outgassing from the evaporating droplets at high relative humidity is hypothesized as the most likely particle formation mechanism but the reason for the temporary appearance of the particle production is not known. [Copyright &y& Elsevier]

Abstract: Aerosol particle number size distributions (3–400nm) were measured for three weeks both indoors and outdoors in a family house with natural ventilation in Espoo, Finland. We investigated the indoor-to-outdoor relationship of aerosol particles and analyzed the effects of indoor activities on the particle number size distributions. We also estimated the decay rate of indoor aerosol particle number concentrations. As expected, in the absence of indoor sources of aerosol particles the indoor particles originated from outdoors and the number concentrations followed similar patterns as those outdoors. The maximum penetration was found for particles between 100 and 400nm in diameter. The mean value of the I/O values was 0.36 for ultrafine particles (UFP diameter &#60;100nm) and 0.60 for particles larger than 100nm in diameter. Because of the penetration and deposition processes of aerosol particles, the modal structure of indoor particle number size distributions had larger geometric mean diameters and significantly lower number concentrations of UFP than those outdoors. The natural ventilation did not provide a stable and controlled indoor-to-outdoor relationship of aerosol particles and it caused variable I/O values and time-lags (10–45min). In the presence of indoor activities, the indoor particle number concentrations cannot be directly estimated from the outdoor number concentrations only. The loss rate of UFP in the indoor air ranged from 1h−1 for 10nm particles to 0.1h−1 for 100nm particles in diameter. The quantitative and qualitative results presented in the current study are building and condition specific. However, the results provide a better understanding of the particle number size distribution characterizations indoors, especially during different indoor activities. [Copyright &y& Elsevier]

Abstract: Particle number size distributions were measured in the urban and suburban atmosphere of Helsinki. In the absence of a direct traffic emission influence, the temporal variation of the aerosol particle number concentrations and their particle size distribution characteristics can be generalized within the Helsinki metropolitan region. In general, the particle number size distributions are characterized by three modes: nucleation (&#60;25nm), Aitken (25–90nm), and accumulation (>90nm). Under certain conditions such as overlapping between the nucleation and Aitken modes, it is possible to characterize the particle number size distributions by two modes: ultrafine mode (&#60;100nm) and accumulation mode (>100nm). Traffic combustions are considered as one of the major sources of ultrafine particles (UFP, ) in the urban atmosphere. The total particle number concentration is highest in the urban centers (as high as 140000cm−3, more than 90% is UFP), In general, 70–80% of the submicrometer particle number concentration is UFP in the suburban atmosphere. Close to major highways, the geometric mean diameters of the submicrometer modes are smaller and the total number concentrations can exceed 60000cm−3 (more than 60% is nucleation mode particles). According to the wind speed and temperature analysis, the submicrometer aerosol particles in the urban and suburban atmosphere consist of two components: UFP that is diluted with wind speeds and inversely proportional to the ambient temperature, and particles larger than 100nm in diameter that is re-suspended with wind and proportional to the ambient temperature. The correlation analysis showed that UFP number concentrations are best correlated within the urban areas. Particles larger than 100nm showed good correlation factors (about 0.80) within the Helsinki metropolitan area, which is an indication of similar kinds of aerosols such as regional transported particles. [Copyright &y& Elsevier]

This study present real-time measurements of the chemical composition and particle number size distributions (PNSD) of submicron particulate matter (PM 1) in winter at a coastal industrial park in the Yangtze River Delta region of China. Positive matrix factorization (PMF) analysis identified three PNSD factors and three organic aerosol (OA) factors. Contributions and potential source regions of these factors were investigated for four typical periods during the PM 1 formation and dissipation process. Results show that the relative contributions from aged 250 nm- factor, fresh 35 nm- and 80 nm- factors were strongly affected by local fresh emissions and regional new particle formation. The non-refractory PM 1 measured by Aerodyne aerosol chemical speciation monitor is indicative of the chemical composition of aged 250 nm-factor, but not fresh 35 nm- and 80 nm-factors. The contributions of NO 3 − and SO 4 2− to NR-PM 1 were largely dictated by whether the air mass trajectory went over the sea or the continent. NO 3 − was abundant (up to 44% of NR-PM 1) in cold and dry continental air masses, while SO 4 2− formation (up to 39% of NR-PM 1) was preferred in humid and warm marine air masses. Among the three OA source factors, more-oxidized oxygenated OA (MO-OOA) was the most abundant OA factor (44–66% of total OA) throughout the entire field campaign, while an enhanced contribution of 39% from hydrocarbon-like OA (HOA) was observed prior to heavy pollution period. On average, secondary components SO 4 2−, NO 3 −, NH 4 +, MO-OOA and less-oxidized oxygenated OA (LO-OOA) contributed 90 ± 7% of NR-PM 1 , while primary components HOA and Cl− accounted for the remaining 10 ± 7%. Unlabelled Image • PMF was applied on particle number size distribution and chemical composition data. • Primary and secondary fractions of NR-PM 1 were discriminated based on PMF results. • Four typical periods during the PM formation and dissipation process were investigated. • Source contributions and potential source regions were identified for the four periods. [ABSTRACT FROM AUTHOR]

Ultrafine particles (UFP) pose a risk to human health, but due to the multitude of sources and fast transformation in the urban atmosphere, quantifying the exposure is challenging. Furthermore, physical properties of aerosol particles depend on the particle size. Statistical models are used to quantify spatial and temporal variation of UFP, but rarely used for particle number size distribution (PNSD). The aim of the study was to establish an interpretable statistical model capturing spatial and temporal variation of urban PNSDs using generalized additive models (GAM) and multivariate adaptive regression spline models (MARS). These algorithms automatically fit interpretable, non-linear marginal function to represent relationships between explanatory and response variables. Three different approaches were evaluated to cope with the multidimensionality of the PNSD data (20–800 nm, 34 size bins): a generalized additive model for the particle number concentration (PNC) of every individual size bin (GAM bins), a generalized additive model for the parameters of the PNSD function (GAM pams) and a multivariate adaptive regression spline model for the PNC of every size bin (MARS bins). Reanalysis data of meteorological quantities, urban geometry parameters and approximated traffic counts were used as explanatory variables. Marginal functions of the final models could be attributed to major processes that contribute to spatial and temporal variation of the PNSD, i.e. emissions from vehicle traffic, transport, dilution, accumulation, deposition and new particle formation. Cross-validation coefficients of determination ranged between 0.27 and 0.48 for most size bins. Nonetheless, the modelling approaches resulted in similar root mean square errors (RMSE) and mean absolute error (MAE). Though direct spatial transferability of the models is limited, the presented approaches may be useful for estimating ambient exposure to particles. Image 1 • GAM and MARS algorithms were used on urban particle number size distributions (PNSD). • Three approaches were evaluated to cope with the multidimensionality of PNSD data. • Reanalysis data, urban geometry and traffic were used as explanatory variables. • The models capture important processes involving spatio-temporal PNSD variation. • Cross-validation R2 ranged between 0.27 and 0.48 for most size bins. [ABSTRACT FROM AUTHOR]

Cloud condensation nuclei (CCN) play an important role in the formation and evolution of cloud droplets. However, the dataset of global CCN number concentration (N CCN) is still scarce due to the lack of direct CCN measurements, hindering an accurate evaluation of its climate effects. Alternative approaches to determine N CCN have thus been proposed to calculate N CCN based on measurements of other aerosol properties, such as particle number size distribution, bulk aerosol chemical composition and aerosol optical properties. To better understand the interaction between haze pollution and climate, we performed direct CCN measurements in the winter of 2018 at the Gucheng site, a typical polluted suburban site in North China Plain (NCP). The results show that the average CCN concentrations were 3.81 × 103 cm−3, 5.35 × 103 cm−3, 9.74 × 103 cm−3, 1.27 × 104 cm−3, 1.44 × 104 cm−3 at measured supersaturation levels of 0.114%, 0.148%, 0.273%, 0.492% and 0.864%, respectively. Based on these observational data, we have further investigated two methods of calculating N CCN from: (1) bulk aerosol chemical composition and particle number size distribution; (2) bulk aerosol chemical composition and aerosol optical properties. Our results showed that both methods could well reproduce the observed concentration (R 2 > 0.88) and variability of N CCN with a 9% to 23% difference in the mean value. Further error analysis shows that the estimated N CCN tends to be underestimated by about 20% during the daytime while overestimated by <10% at night compared with the measured N CCN. These results provide quantitative instructions for the N CCN prediction based on conventional aerosol measurements in the NCP. Unlabelled Image • Conventional measurements of PNSD and bulk aerosol chemical composition perform well in predicting N CCN • The estimation of N CCN based on conventional measurements of AOP can be applicable under SSs lower than 0.114% • Relative deviations between calculated and measured N CCN suggest significant diurnal variations of aerosol hygroscopicity. [ABSTRACT FROM AUTHOR]