Atmospheric Particle Number Size Distributions 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.

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.

Cluster analysis of atmospheric particle number size distributions at a rural site downwind of Seoul, Korea

We identified seven clusters from SMPS measurements ranging from 10 to 291 nm using k-means clustering, representing background (BG), local emissions (LocEm), two types of traffic emissions (TR), and three types of nucleation (NC). BG and LocEm differed in that pollutant concentrations were low and high, respectively, but both exhibited less pronounced diurnal variations in the frequency of occurrence. TR was divided into larger particles peaking at 72 nm and smaller particles with a primary peak at ~10 nm and a secondary peak at 72 nm. Because the main road is more than 1 km away from the study site, the primary peak consisting of smaller particles in the nucleation mode disappeared in most cases. However, when being affected directly from vehicle emissions, the primary peak size was reduced by the volatilization of semi-volatile substances. NC was divided into NC (fresh), NC (aged), and NC (trans) denoting nucleated far away and transported. NC (fresh) had a peak size of 21 nm and a peak time of 13:00, along with typical conditions favorable for new particle formation (NPF). The highest ozone and lowest PM10 concentrations for NC (aged) were conducive to particle growth, because semi-volatile substances were actively produced, while the condensation sink of these substances onto pre-existing particles was unavailable. Many characteristics of NC (trans) were similar to BG and LocEm, indicating NPF over a wider area. Because of the distance to the main road, the contribution to the nucleation mode was 44% for NC, higher than 26% for TR.

New Particle Formation Events in Summer and Winter in the Coastal Atmosphere in Qingdao, China

Atmospheric particle number size distributions were measured by a wide-range particle size spectrometer and a scanning mobility particle size spectrometer in the summertime and wintertime in the coastal area of Qingdao (China). The inorganic and organic gaseous precursors and particulate chemical composition were measured to characterize new particle formation (NPF) events by combining meteorological parameters and backward trajectories. In summer, the occurrence frequency of NPF events was 18% lower. However, the atmospheric particle number concentration increased by approximately 1-4 times during the NPF events compared with those without NPF. The apparent formation rates and growth rates were (5.2±4.3) cm-3·s-1 and (6.5±2.2) nm·h-1, respectively, except for a special NPF event on July 20. The correlation analysis results implied that biogenic volatile organic compounds (BVOCs) seemingly favor NPF, and the reverse is true for anthropogenic volatile organic compounds (AVOCs). The occurrence frequency of NPF events of 27% in winter was clearly higher than that in summer. The apparent formation rates and growth rates, i.e., (3.3±3.1) cm-3·s-1 and (5.3±3.3) nm·h-1, decreased, although the decreases were not significant (P>0.05). The correlation analyses implied that AVOCs favored NPF. However, BVOCs had no correlation with NPF. For the cases in which new particles could grow to CCN sizes (>50 nm), the particle growth characteristics showed significant seasonal differences, i.e., in summer, new particles could grow to CCN sizes via photochemical reactions, whereas in winter, second-stage growth driven by the formation of nitrate aerosols was needed to grow new particles to CCN sizes.

Temporal and spatial variability of atmospheric particle number size distributions across Spain

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.

Statistical modelling of aerosol particle number size distributions in urban and rural environments – A multi-site study

A multiple linear regression approach was used to model the urban atmospheric particle number size distribution (NSD) at 11 different sites (roadside, urban background, rural) in Central European cities for the time period 2008–2010. The same set of 13 model input parameters, consisting of temporal information (daytime, season) and meteorological measurement data, was used at each site.NSD model performance indicates an average deviation between observations and model (Bias) in the order of<10% with respect to total particle number concentration. The most reliable predictions were achieved for roadside sites with correlation coefficients (R) of 0.75 on average and a normalized root mean square error (RMSEn) of 0.79. Limited performance was observed for rural sites (R=0.61; RMSEn∼1.2). The transferability of the model approach to an independent urban background site was tested showing R of 0.5 and normalized RMSEn of 1.4. Although the physical relationship between particle NSD, ambient meteorological conditions and the temporal parameters are extremely complex, the model was able to reproduce the variation in particle concentrations. As a first in the field this study focused on modelling the entire number size distribution in contrast to size integrated particle number concentrations.

Assessment and application of clustering techniques to atmospheric particle number size distribution for the purpose of source apportionment

Abstract. Long-term measurements of particle number size distribution (PNSD) produce a very large number of observations and their analysis requires an efficient approach in order to produce results in the least possible time and with maximum accuracy. Clustering techniques are a family of sophisticated methods that have been recently employed to analyse PNSD data; however, very little information is available comparing the performance of different clustering techniques on PNSD data. This study aims to apply several clustering techniques (i.e. K means, PAM, CLARA and SOM) to PNSD data, in order to identify and apply the optimum technique to PNSD data measured at 25 sites across Brisbane, Australia. A new method, based on the Generalised Additive Model (GAM) with a basis of penalised B-splines, was proposed to parameterise the PNSD data and the temporal weight of each cluster was also estimated using the GAM. In addition, each cluster was associated with its possible source based on the results of this parameterisation, together with the characteristics of each cluster. The performances of four clustering techniques were compared using the Dunn index and Silhouette width validation values and the K means technique was found to have the highest performance, with five clusters being the optimum. Therefore, five clusters were found within the data using the K means technique. The diurnal occurrence of each cluster was used together with other air quality parameters, temporal trends and the physical properties of each cluster, in order to attribute each cluster to its source and origin. The five clusters were attributed to three major sources and origins, including regional background particles, photochemically induced nucleated particles and vehicle generated particles. Overall, clustering was found to be an effective technique for attributing each particle size spectrum to its source and the GAM was suitable to parameterise the PNSD data. These two techniques can help researchers immensely in analysing PNSD data for characterisation and source apportionment purposes.

Mobility particle size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions

Abstract. Mobility particle size spectrometers often referred to as DMPS (Differential Mobility Particle Sizers) or SMPS (Scanning Mobility Particle Sizers) have found a wide range of applications in atmospheric aerosol research. However, comparability of measurements conducted world-wide is hampered by lack of generally accepted technical standards and guidelines with respect to the instrumental set-up, measurement mode, data evaluation as well as quality control. Technical standards were developed for a minimum requirement of mobility size spectrometry to perform long-term atmospheric aerosol measurements. Technical recommendations include continuous monitoring of flow rates, temperature, pressure, and relative humidity for the sheath and sample air in the differential mobility analyzer. We compared commercial and custom-made inversion routines to calculate the particle number size distributions from the measured electrical mobility distribution. All inversion routines are comparable within few per cent uncertainty for a given set of raw data. Furthermore, this work summarizes the results from several instrument intercomparison workshops conducted within the European infrastructure project EUSAAR (European Supersites for Atmospheric Aerosol Research) and ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network) to determine present uncertainties especially of custom-built mobility particle size spectrometers. Under controlled laboratory conditions, the particle number size distributions from 20 to 200 nm determined by mobility particle size spectrometers of different design are within an uncertainty range of around ±10% after correcting internal particle losses, while below and above this size range the discrepancies increased. For particles larger than 200 nm, the uncertainty range increased to 30%, which could not be explained. The network reference mobility spectrometers with identical design agreed within ±4% in the peak particle number concentration when all settings were done carefully. The consistency of these reference instruments to the total particle number concentration was demonstrated to be less than 5%. Additionally, a new data structure for particle number size distributions was introduced to store and disseminate the data at EMEP (European Monitoring and Evaluation Program). This structure contains three levels: raw data, processed data, and final particle size distributions. Importantly, we recommend reporting raw measurements including all relevant instrument parameters as well as a complete documentation on all data transformation and correction steps. These technical and data structure standards aim to enhance the quality of long-term size distribution measurements, their comparability between different networks and sites, and their transparency and traceability back to raw data.

First long-term study of particle number size distributions and new particle formation events of regional aerosol in the North China Plain

Abstract. Atmospheric particle number size distributions (size range 0.003–10 μm) were measured between March 2008 and August 2009 at Shangdianzi (SDZ), a rural research station in the North China Plain. These measurements were made in an attempt to better characterize the tropospheric background aerosol in Northern China. The mean particle number concentrations of the total particle, as well as the nucleation, Aitken, accumulation and coarse mode were determined to be 1.2 ± 0.9 × 104, 3.6 ± 7.9 × 103, 4.4 ± 3.4 × 103, 3.5 ± 2.8 × 103 and 2 ± 3 cm−3, respectively. A general finding was that the particle number concentration was higher during spring compared to the other seasons. The air mass origin had an important effect on the particle number concentration and new particle formation events. Air masses from northwest (i.e. inner Asia) favored the new particle formation events, while air masses from southeast showed the highest particle mass concentration. Significant diurnal variations in particle number were observed, which could be linked to new particle formation events, i.e. gas-to-particle conversion. During particle formation events, the number concentration of the nucleation mode rose up to maximum value of 104 cm−3. New particle formation events were observed on 36% of the effective measurement days. The formation rate ranged from 0.7 to 72.7 cm−3 s−1, with a mean value of 8.0 cm−3 s−1. The value of the nucleation mode growth rate was in the range of 0.3–14.5 nm h−1, with a mean value of 4.3 nm h−1. It was an essential observation that on many occasions the nucleation mode was able to grow into the size of cloud condensation nuclei (CCN) within a matter of several hours. Furthermore, the new particle formation was regularly followed by a measurable increase in particle mass concentration and extinction coefficient, indicative of a high abundance of condensable vapors in the atmosphere under study.

Subarctic atmospheric aerosol composition: 3. Measured and modeled properties of cloud condensation nuclei

Aerosol particles can modify cloud properties by acting as cloud condensation nuclei (CCN). Predicting CCN properties is still a challenge and not properly incorporated in current climate models. Atmospheric particle number size distributions, hygroscopic growth factors, and polydisperse CCN number concentrations were measured at the remote subarctic Stordalen mire, 200 km north of the Arctic Circle in northern Sweden. The CCN number concentration was highly variable, largely driven by variations in the total number of sufficiently large particles, though the variability of chemical composition was increasingly important for decreasing supersaturation. The hygroscopicity of particles measured by a hygroscopicity tandem differential mobility analyzer (HTDMA) was in agreement with large critical diameters observed for CCN activation (κ ≈ 0.07–0.21 for D = 50–200 nm). Size distribution and time‐ and size‐resolved HTDMA data were used to predict CCN number concentrations. Agreement of predictions with measured CCN within ±11% was achieved using parameterized Köhler theory and assuming a surface tension of pure water. The sensitivity of CCN predictions to various simplifying assumptions was further explored: We found that (1) ignoring particle mixing state did not affect CCN predictions, (2) averaging the HTDMA data in time with retaining the size dependence did not introduce a substantial bias, while individual predictions became more uncertain, and (3) predictions involving the hygroscopicity parameter recommended in literature for continental sites (κ ≈ 0.3 ± 0.1) resulted in a significant prediction bias. Future modeling studies should therefore at least aim at using averaged, size‐resolved, site‐specific hygroscopicity or chemical composition data for predictions of CCN number concentrations.

Dispersion of traffic-related exhaust particles near the Berlin urban motorway – estimation of fleet emission factors

Abstract. Atmospheric particle number size distributions of airborne particles (diameter range 10–500 nm) were collected over ten weeks at three sites in the vicinity of the A100 urban motorway in Berlin, Germany. The A100 carries about 180 000 vehicles on a weekday. The roadside particle distributions showed a number maximum between 20 and 60 nm clearly related to the motorway emissions. The average total number concentration at roadside was 28 000 cm−3 with a total range of 1200–168 000 cm−3. At distances of 80 and 400 m from the motorway the concentrations decreased to mean levels of 11 000 and 9000 cm−3, respectively. An obstacle-resolving dispersion model was applied to simulate the 3-D flow field and traffic tracer transport in the urban environment around the motorway. By inverse modelling, vehicle emission factors were derived that are representative of a fleet with a relative share of 6% lorry-like vehicles, and driving at a speed of 80 km h−1. Three different calculation approaches were compared, which differ in the choice of the experimental winds driving the flow simulation. The average emission factor per vehicle was 2.1 (±0.2) · 1014 km−1 for particle number and 0.077 (±0.01) · 1014 cm3 km−1 for particle volume. Regression analysis suggested that lorry-like vehicles emit 123 (±28) times more particle number than passenger car-like vehicles, and lorry-like vehicles account for about 91% of particulate number emissions on weekdays. Our work highlights the increasing applicability of 3-D flow models in urban microscale environments and their usefulness for determining traffic emission factors.

Atmospheric particle number size distribution in central Europe: Statistical relations to air masses and meteorology

Atmospheric particle number size distributions determined over 1.5 years at a central European site were statistically analyzed in terms of their relation to time of day, season, meteorology, and synoptic‐scale air masses. All size distributions were decomposed into lognormal particle modes corresponding to the accumulation, Aitken, aged nucleation, and nucleation modes. The concentration of nucleation mode particles (&lt;30 nm) behaved in a strongly diurnal fashion as a result of both anthropogenic source influence and secondary new particle formation events. The concentrations of Aitken and accumulation mode particles (&gt;30 nm) lacked such diurnal behavior, and proved to be indicative of different synoptic‐scale air mass types. Over 70% of the time, air masses of Atlantic origin and maritime character prevailed, showing obvious signs of anthropogenic influence most of the time (accumulation mode: 500 cm−3; Aitken mode: 2300 cm−3). During a limited period of time (10%), however, continentally aged air with significantly enhanced concentrations of aerosol was observed (accumulation mode: 1200 cm−3; Aitken mode: 3300 cm−3). These air masses were advected from source regions in Russia, and eastern, southeastern, and central Europe, mainly under anticyclonic and high‐pressure influence. The analysis provides a refined picture of the behavior of the particle number size distribution and provides parameterizations that are representative for a variety of air masses in Europe and thus suitable for future climate modeling applications.