Particle Number Concentration Measurements Research Articles

Tethered balloon measurements reveal enhanced aerosol occurrence aloft interacting with Arctic low-level clouds

Low-level clouds in the Arctic affect the surface energy budget and vertical transport of heat and moisture. The limited availability of cloud-droplet-forming aerosol particles strongly impacts cloud properties and lifetime. Vertical particle distributions are required to study aerosol–cloud interaction over sea ice comprehensively. This article presents vertically resolved measurements of aerosol particle number concentrations and sizes using tethered balloons. The data were collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition in the summer of 2020. Thirty-four profiles of aerosol particle number concentration were observed in 2 particle size ranges: 12–150 nm (N12−150) and above 150 nm (N>150). Concurrent balloon-borne meteorological measurements provided context for the continuous profiles through the cloudy atmospheric boundary layer. Radiosoundings, cloud remote sensing data, and 5-day back trajectories supplemented the analysis. The majority of aerosol profiles showed more particles above the lowest temperature inversion, on average, double the number concentration compared to below. Increased N12−150 up to 3,000 cm−3 were observed in the free troposphere above low-level clouds related to secondary particle formation. Long-range transport of pollution increased N>150 to 310 cm−3 in a warm, moist air mass. Droplet activation inside clouds caused reductions of N>150 by up to 100%, while the decrease in N12−150 was less than 50%. When low-level clouds were thermodynamically coupled with the surface, profiles showed 5 times higher values of N12−150 in the free troposphere than below the cloud-capping temperature inversion. Enhanced N12−150 and N>150 interacting with clouds were advected above the lowest inversion from beyond the sea ice edge when clouds were decoupled from the surface. Vertically discontinuous aerosol profiles below decoupled clouds suggest that particles emitted at the surface are not transported to clouds in these conditions. It is concluded that the cloud-surface coupling state and free tropospheric particle abundance are crucial when assessing the aerosol budget for Arctic low-level clouds over sea ice.

OPC-Pod: A New Sensor Payload to Measure Aerosol Particles for Small Uncrewed Aircraft Systems

Abstract Atmospheric aerosols affect human health and influence atmospheric and biological processes. Dust can be transported long distances in the atmosphere, and the mechanisms that influence dust transport are not fully understood. To improve the database for numerical models that simulate dust transport, measurements are needed that cover both the vertical distribution of the dust and its size distribution. In addition to measurements with crewed aircraft, uncrewed aircraft systems (UASs) provide a particularly suitable platform for this purpose. In this paper, we present a payload for the small fixed-wing UAS of the type Multiple-Purpose Airborne Sensor Carrier 3 (MASC-3) for aerosol particle measurements that is based on the optical particle counter (OPC) OPC-N3 (Alphasense, United Kingdom), modified by the addition of a dryer and a passive aspiration system (OPC-Pod). Based on field tests with a reference instrument in Mannheim, Germany, wind tunnel tests, and a comparison measurement with the UAS-mounted aerosol particle measurement Universal Cloud and Aerosol Sounding System (UCASS) during a dust event over Cyprus, we show that the OPC-Pod can measure particle number concentrations in the range of 0.66–31 μm as well as particle size distributions. The agreement of the OPC-Pod with UCASS is good. Both instruments resolve a vertical profile of the Saharan dust event, with a prominent dust layer between 1500 and 2800 m MSL, with particle number concentrations up to 35 cm−3 for particles between 0.66 and 31 μm.

Contrasting intra-urban variability of ultrafine particle number and fine particle mass concentrations in Dhaka, Bangladesh, and Pittsburgh, USA

In this study, we investigated the intra-urban variability of fine particle mass (PM2.5) and ultrafine particle number concentration (PNC) in Dhaka (Bangladesh), and Pittsburgh (USA), two cities with vastly different pollution sources and levels. We collected measurements of PNC and PM2.5 at a wide range of sites spanning a variety of urban land use attributes (35 sites in Dhaka and 30 sites in Pittsburgh). We found that PNC levels exhibited a 3-4-fold variability between sites in each city, ranging from 20,000–100,000 # cm−3 in Dhaka and 7,000–28,000 # cm−3 in Pittsburgh. PM2.5 levels varied within 50% of the urban background level, ranging from 80 to 110 μg m−3 in Dhaka and 6–12 μg m−3 in Pittsburgh. We observed a moderate level of spatial correlation between PNC and PM2.5 measurements in both cities (R2 0.3 in Dhaka, and 0.4 in Pittsburgh), and consistent within-city spatial patterns in different meteorological seasons. Compared to the Pittsburgh levels, both PNC and PM2.5 levels in Dhaka were significantly higher, however, PM2.5 was disproportionately higher (10–12 times higher) than PNC (3–4 times higher). The slope of PNC versus PM2.5 varied significantly between the two cities, suggesting that the sources and size distribution of particles that make up the majority of the PM2.5 were different in the two cities. The results found in Dhaka indicate that aerosol particles are influenced by solid fuel combustion, including solid biomass burning, waste burning, and road dust, which have a greater impact on particle mass concentration due to their larger size. Contrary, in Pittsburgh, traffic (gasoline and diesel combustion) particles, relatively smaller in size compared to solid fuel combustion particles, play a dominant role in determining the within-city variability of PNC and PM2.5. Our findings suggest that while controlling traffic emissions can contribute to reducing PNC, substantial efforts will be required to mitigate accumulation mode particles from various region-specific sources in order to decrease PM2.5 mass concentrations in Dhaka.

Reply to “Comment on Comparison of direct and indirect measures of transport efficiency in single particle inductively coupled plasma mass spectrometry” by H. Goenaga-Infante

This paper provides a rebuttal to the comments on our original research article entitled “Comparison of Direct and Indirect Measures of Transport Efficiency in Single Particle ICP-MS” recently published by Goenaga-Infante in Spectrochimica Acta Part B: Atomic Spectroscopy.The intent of our study is not to condemn the dynamic mass flow (DMF) method but rather to explore the use parameters under which it can and cannot be applied. As explained in the original paper, the goal of this study is to evaluate the ranges of use conditions under which measures of transport efficiency (TE) yield accurate and reproducible results for spICP-MS measurements of particle number concentration (PNC) and particle size (diameter, PS) of various gold nanoparticle (AuNP) suspensions. The evaluation was performed through a systematic comparison of three methods for the measurement of TE: the particle frequency (TEF), particle size (TES), and DMF methods using three types of spray chambers operated at cooled and ambient temperature conditions and employing different ICP-MS platforms. While we appreciate thorough critical and constructive comments on our paper, we strongly disagree that the conclusions and highlights are not supported by the content and findings about the features and benefits of the DMF method.The discussion of three additional independent studies in this field by other spICP-MS expert groups that have been published after the submission of our manuscript is included in this paper. While the DMF approach has been used in two interlaboratory comparisons for TE determination in spICP-MS measurements of PNC, only one laboratory, namely the laboratory led by Goenaga-Infante, provided results using the DMF method in both projects. A method cannot be considered validated if successful results have only been demonstrated within one laboratory.The paper by Goenaga-Infante claims that the main use of DMF, the assignment of a SI traceable PNC value to new commercial nanomaterials (NMs), has not been highlighted explicitly in our original paper. The advantages and disadvantages of the DMF, TES, and TEF methods to measure TE were presented throughout the manuscript and are clearly summarized in the conclusion. The assignment of PNC that is metrologically traceable to the SI implies that all known or suspected uncertainty components including bias are taken into account. Our research shows that under some use conditions, the biases inherent to the DMF method are not yet fully understood and cannot be accounted for. While Cuello-Nuñez et al. Journal of Analytical Atomic Spectrometry, 2020, DOI: https://doi.org/10.1039/c9ja00415g state that cooled conditions (2 °C) were used in their work, they do not define the level of bias that can be expected if different spray chamber temperatures are used, and they do not provide recommendations on the optimal use conditions that define the field of applicability of the DMF method. Furthermore, besides the use of a Scott-type spray chamber cooled to 2 °C, neither the composition material of the spray chamber nor the volume of the Scott-type spray chamber were specified. It is important to note that in our original research, fifteen of the nineteen experiments were conducted using a cooled spray chamber. Also, the four different ICP-MS platforms were used in the standard configuration and with additional spray chamber options encountered in common ICP-MS usage. The value of our work is that it extends the study of Cuello-Nuñez et al. to a wide variety of use conditions routinely encountered in spICP-MS analysis.

Two new multirotor uncrewed aerial vehicles (UAVs) for glaciogenic cloud seeding and aerosol measurements within the CLOUDLAB project

Abstract. Uncrewed aerial vehicles (UAVs) have become widely used in a range of atmospheric science research applications. Because of their small size, flexible range of motion, adaptability, and low cost, multirotor UAVs are especially well-suited for probing the lower atmosphere. However, their use so far has been limited to conditions outside of clouds, first because of the difficulty of flying beyond visual line of sight and second because of the challenge of flying in icing conditions in supercooled clouds. Here, we present two UAVs for cloud microphysical research: one UAV (the measurement UAV) equipped with a Portable Optical Particle Spectrometer (POPS) and meteorological sensors to probe the aerosol and meteorological properties in the boundary layer and one UAV (the seeding UAV) equipped with seeding flares to produce a plume of particles that can nucleate ice in supercooled clouds. A propeller heating mechanism on both UAVs allows for operating in supercooled clouds with icing conditions. These UAVs are an integral part of the CLOUDLAB project in which glaciogenic cloud seeding of supercooled low stratus clouds is utilized for studying aerosol–cloud interactions and ice crystal formation and growth. In this paper, we first show validations of the POPS on board the measurement UAV, demonstrating that the rotor turbulence has a small effect on measured particle number concentrations. We then exemplify the applicability for profiling the planetary boundary layer, as well as for sampling and characterizing aerosol plumes, in this case, the seeding plume. We also present a new method for filtering out high-concentration data to ensure good data quality of POPS. We explain the different flight patterns that are possible for both UAVs, namely horizontal or vertical leg patterns or hovering, with an extensive and flexible parameter space for designing the flight patterns according to our scientific goals. Finally, we show two examples of seeding experiments: first characterizing an out-of-cloud seeding plume with the measurement UAV flying horizontal transects through the plume and, second, characterizing an in-cloud seeding plume with downstream measurements from a POPS and a holographic imager mounted on a tethered balloon. Particle number concentrations and particle number size distributions of the seeding plume from the experiments reveal that we can successfully produce and measure the seeding plume, both in-cloud (with accompanying elevated ice crystal number concentrations) and out-of-cloud. The methods presented here will be useful for probing the lower atmosphere, for characterizing aerosol plumes, and for deepening our cloud microphysical understanding through cloud seeding experiments, all of which have the potential to benefit the atmospheric science community.

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.

Numerical simulation and evaluation of global ultrafine particle concentrations at the Earth's surface

Abstract. A new global dataset of annually averaged ultrafine particle (UFP) concentrations at the Earth's surface for the years 2015–2017 has been developed through numerical simulations using the ECHAM/MESSy Atmospheric Chemistry model (EMAC). We present total and size-resolved concentrations along with their interannual variability. Size distributions of emitted particles from the contributing source sectors have been derived based on literature reports. The model results of UFP concentrations are evaluated using particle size distribution and particle number concentration measurements from available datasets and the literature. While we obtain reasonable agreement between the model results and observations (logarithmic-scale correlation of r=0.76 for non-remote, polluted regions), the highest values of observed, street-level UFP concentrations are systematically underestimated, whereas in rural environments close to urban areas the model generally overestimates observed UFP concentrations. As the relatively coarse global model does not resolve concentration gradients in urban centres and industrial UFP hotspots, high-resolution data of anthropogenic emissions are used to account for such differences in each model grid box, obtaining UFP concentrations with unprecedented 0.1∘×0.1∘ horizontal resolution at the Earth's surface. This observation-guided downscaling further improves the agreement with observations, leading to an increase in the logarithmic-scale correlation between observed and simulated UFP concentrations to r=0.84 in polluted environments (and 0.95 in all regions), a decrease in the root mean squared logarithmic error (from 0.57 to 0.43), and removal of discrepancies associated with air quality and population density gradients within the model grid boxes. The model results are made publicly available for studies on public health and other impacts of atmospheric UFPs, as well as for intercomparison with other regional and global models and datasets.

Exhaust particle number and composition for diesel and gasoline passenger cars under transient driving conditions: Real-world emissions down to 1.5 nm

Recent recommendations given by WHO include systematic measurements of ambient particle number concentration and black carbon (BC) concentrations. In India and several other highly polluted areas, the air quality problems are severe and the need for air quality related information is urgent. This study focuses on particle number emissions and BC emissions of passenger cars that are technologically relevant from an Indian perspective. Particle number and BC were investigated under real-world conditions for driving cycles typical for Indian urban environments. Two mobile laboratories and advanced aerosol and trace gas instrumentation were utilized. Our study shows that passenger cars without exhaust particle filtration can emit in real-world conditions large number of particles, and especially at deceleration a significant fraction of particle number can be even in 1.5–10 nm particle sizes. The mass concentration of exhaust plume particles was dominated by BC that was emitted especially at acceleration conditions. However, exhaust particles contained also organic compounds, indicating the roles of engine oil and fuel in exhaust particle formation. In general, our study was motivated by serious Indian air quality problems, by the recognized lack of emission information related to Indian traffic, and by the recent WHO air quality guidance; our results emphasize the importance of monitoring particle number concentrations and BC also in Indian urban areas and especially in traffic environments where people can be significantly exposed to fresh exhaust emissions.

Exploring the potential for continuous measurement of ultrafine particle mass concentration (PM 0.1 ) based on measurements of particle number concentration above 50 nm ( N 50 )

Exploring the potential for continuous measurement of ultrafine particle mass concentration (PM _0.1 ) based on measurements of particle number concentration above 50 nm ( <i>N</i> ₅₀ )

Effect of radiation interaction and aerosol processes on ventilation and aerosol concentrations in a real urban neighbourhood in Helsinki

Abstract. Large-eddy simulation (LES) is an optimal tool to examine aerosol particle concentrations in detail within urban neighbourhoods. The concentrations are a complex result of local emissions, meteorology, aerosol processes and local mixing conditions due to thermal and mechanical effects. Despite this, most studies have focused on simplification of the affecting processes such as examining the impact of local mixing in idealised street canyons or treating aerosols as passive scalars. The aim of this study is to include all these processes into LES using the PALM model system and to examine the importance of radiative heating and aerosol processes in simulating local aerosol particle concentrations and different aerosol metrics within a realistic urban neighbourhood in Helsinki under morning rush hour with calm wind conditions. The model outputs are evaluated against mobile laboratory measurements of air temperature and total particle number concentration (Ntot) as well as drone measurements of lung-deposited surface area (LDSA). The inclusion of radiation interaction in LES has a significant impact on simulated near-surface temperatures in our study domain, increasing them on average from 8.6 to 12.4 ∘C. The resulting enhanced ventilation reduces the pedestrian-level (4 m) Ntot by 53 %. The reduction in Ntot due to aerosol processes is smaller, only 18 %. Aerosol processes particularly impact the smallest particle range, whereas radiation interaction is more important in the larger particle range. The inclusion of radiation interaction reduces the bias between the modelled and mobile-laboratory-measured air temperatures from −3.9 to +0.2 ∘C and Ntot from +98 % to −13 %. With both aerosol and radiation interaction on, the underestimation is 16 %, which might be due to overestimation of the ventilation. The results show how inclusion of radiative interaction is particularly important in simulating PM2.5, whereas aerosol processes are more important in simulating LDSA in this calm wind situation.

Characterisation of a self-sustained, water-based condensation particle counter for aircraft cruising pressure level operation

Abstract. Aerosol particle number concentration measurements are a crucial part of aerosol research. Vertical profile measurements and high-altitude/low-pressure performance of the respective instruments become more important for remote sensing validation and a vital tool for the observation of climate variables. This study tests the new, commercially available water condensation particle counter (MAGIC 210-LP) for the deployment at aircraft cruising pressure levels that the European research infrastructure IAGOS (In-service Aircraft for a Global Observing System; http://www.iagos.org, last access: 2 May 2023) is aiming for by operating measurement instrumentation onboard passenger aircraft. We conducted laboratory experiments for conditions to simulate passenger aircraft flight altitude at operation pressure. We demonstrate that this type of water condensation particle counter shows excellent agreement with a butanol-based instrument used in parallel. A Faraday cup aerosol electrometer serves as the reference instrument. Experiments are performed with test aerosol ammonium sulfate and fresh combustion soot at pressure levels ranging from 700 to 200 hPa. For soluble particles like ammonium sulfate, the 50 % detection efficiency cut-off diameter (D50) is around 5 nm and does not differ significantly for all performed experiments. For non-soluble fresh soot particles, the D50 cut-off diameter of approximately 10 nm does not vary substantially as a function of pressure, whereas the 90 % detection efficiency cut-off diameter D90 increases from 19 nm at 700 hPa to 37 nm at 200 hPa. The overall counting efficiency for particles larger than 40 nm reaches 100 % for working pressures of 200 hPa and higher.

Investigating the Sensitivity of Low-Cost Sensors in Measuring Particle Number Concentrations across Diverse Atmospheric Conditions in Greece and Spain.

Low-cost sensors (LCSs) for particulate matter (PM) concentrations have attracted the interest of researchers, supplementing their efforts to quantify PM in higher spatiotemporal resolution. The precision of PM mass concentration measurements from PMS 5003 sensors has been widely documented, though limited information is available regarding their size selectivity and number concentration measurement accuracy. In this work, PMS 5003 sensors, along with a Federal Referral Methods (FRM) sampler (Grimm spectrometer), were deployed across three sites with different atmospheric profiles, an urban (Germanou) and a background (UPat) site in Patras (Greece), and a semi-arid site in Almería (Spain, PSA). The LCSs particle number concentration measurements were investigated for different size bins. Findings for particles with diameter between 0.3 and 10 μm suggest that particle size significantly affected the LCSs' response. The LCSs could accurately detect number concentrations for particles smaller than 1 μm in the urban (R2 = 0.9) and background sites (R2 = 0.92), while a modest correlation was found with the reference instrument in the semi-arid area (R2 = 0.69). However, their performance was rather poor (R2 < 0.31) for coarser aerosol fractions at all sites. Moreover, during periods when coarse particles were dominant, i.e., dust events, PMS 5003 sensors were unable to report accurate number distributions (R2 values < 0.47) and systematically underestimated particle number concentrations. The results indicate that several questions arise concerning the sensors' capabilities to estimate PM2.5 and PM10 concentrations, since their size distribution did not agree with the reference instruments.

Observations of Fog‐Aerosol Interactions Over Central Greenland

AbstractSupercooled fogs can have an important radiative impact at the surface of the Greenland Ice Sheet, but they are difficult to detect and our understanding of the factors that control their lifetime and radiative properties is limited by a lack of observations. This study demonstrates that spectrally resolved measurements of downwelling longwave radiation can be used to generate retrievals of fog microphysical properties (phase and particle effective radius) when the fog visible optical depth is greater than ∼0.25. For 12 cases of fog under otherwise clear skies between June and September 2019 at Summit Station in central Greenland, nine cases were mixed‐phase. The mean ice particle (optically‐equivalent sphere) effective radius was 24.0 ± 7.8 µm, and the mean liquid droplet effective radius was 14.0 ± 2.7 µm. These results, combined with measurements of aerosol particle number concentrations, provide evidence supporting the hypotheses that (a) low surface aerosol particle number concentrations can limit fog liquid water path, (b) fog can act to increase near‐surface aerosol particle number concentrations through enhanced mixing, and (c) multiple fog events in quiescent periods gradually deplete near‐surface aerosol particle number concentrations.

Assessment of the applicability of a model for aviation-related ultrafine particle concentrations for use in epidemiological studies

Background and objectivesIn recent years it has been shown that aircraft emissions are a dominant source of ultrafine particles in the surroundings of airports. However, health effects of long-term (monthly to yearly) exposure to these particles are unknown. As part of an integrated research program into the health risks of ultrafine particles around Schiphol Airport, the applicability of the dispersion model STACKS+ to assess long-term exposure to ultrafine particles from aviation was assessed. MethodologyA detailed comparison between modelled and measured particle number concentrations (PNC) due to aircraft emissions was carried out at ten locations in the surroundings of Schiphol Airport during two six-month periods in 2017 and 2018. In order to deduce the contribution of aviation to measured PNC, we applied a fitting method of the sum of the modelled contributions from aviation, the modelled contributions from traffic on main roads and the contributions from outside the study area estimated from the measurements, to the measured total PNC. The analysis yielded scaling factors and uncertainty estimates for each of the main contributions. We then subtracted the estimated background and modelled contributions of road traffic from the total measured PNC and took the remainder as an approximation of the measured contribution from aviation to PNC. We compared it to the modelled contribution from aviation, based on the averaged values for the six-month periods. ResultsBoth six-month averaged modelled and measured PNC due to aircraft emissions (i.e., adjusted for background) showed a large range at the monitoring locations representative for population exposure (from close to zero to 10 000 particles/cm3). Spearman and Pearson correlation coefficients between model and measurement results were high (>0.83). ConclusionsThe applied approach enabled us to obtain a robust estimate of the contribution of aviation to the measured PNC. The dispersion model is able to determine the spatially varying average concentrations due to aircraft emissions in residential areas over periods of 6 months, allowing for application in epidemiological studies into long-term exposure.

Residual impacts of a wildland urban interface fire on urban particulate matter and dust: a study from the Marshall Fire

The impacts of wildfires along the wildland urban interface (WUI) on atmospheric particulate concentrations and composition are an understudied source of air pollution exposure. To assess the residual impacts of the 2021 Marshall Fire (Colorado), a wildfire that predominantly burned homes and other human-made materials, on homes within the fire perimeter that escaped the fire, we performed a combination of fine particulate matter (PM2.5) filter sampling and chemical analysis, indoor dust collection and chemical analysis, community scale PurpleAir PM2.5 analysis, and indoor particle number concentration measurements. Following the fire, the chemical speciation of dust collected in smoke-affected homes in the burned zone showed elevated concentrations of the biomass burning marker levoglucosan (medianlevo = 4147 ng g−1), EPA priority toxic polycyclic aromatic hydrocarbons (median Σ16PAH = 1859.3 ng g−1), and metals (median Σ20Metals = 34.6 mg g−1) when compared to samples collected in homes outside of the burn zone 6 months after the fire. As indoor dust particles are often resuspended and can become airborne, the enhanced concentration of hazardous metals and organics within dust samples may pose a threat to human health. Indoor airborne particulate organic carbon (median = 1.91 μg m−3), particulate elemental carbon (median = .02 μg m−3), and quantified semi-volatile organic species in PM2.5 were found in concentrations comparable to ambient air in urban areas across the USA. Particle number and size distribution analysis at a heavily instrumented supersite home located immediately next to the burned area showed indoor particulates in low concentrations (below 10 μg m−3) across various sizes of PM (12 nm–20 μm), but were elevated by resuspension from human activity, including cleaning.Graphical

High contribution of new particle formation to ultrafine particles in four seasons in an urban atmosphere in south China

Ultra fine particles (UFP) cover the size range of both nucleation mode particles (NUC, Dp < 25 nm) and Aitken mode particles (AIT, 25 nm < Dp < 100 nm), and play important roles in radiative forcing and human health. In this study, we identified new particle formation (NPF) events and undefined events, explored their potential formation mechanism, and quantified their contributions to UFP number concentration (NUFP) in urban Dongguan of the Pearl River Delta (PRD) region. Field campaigns were carried out in four seasons in 2019 to measure particle number concentration in the size range of 4.7–673.2 nm, volatile organic compounds (VOCs), gaseous pollutants, chemical compositions in PM2.5, and meteorological parameters. The frequency of the occurrence of NPF, as indicated by a significant increase in NUC number concentration (NNUC), was 26 %, and that of the undefined event, as indicated by substantial increases in NNUC or AIT number concentration (NAIT), was 32 % during the whole campaign period. The NPF events mainly occurred in autumn (with a frequency of 59 %) and winter (33 %) and only occasionally in spring (4 %) and summer (4 %). On the contrary, the frequencies of the undefined events were higher in spring (52 %) and summer (38 %) than in autumn (19 %) and winter (22 %). The burst periods of the NPF events mainly occurred before 11:00 Local Time (LT), while those of the undefined events mainly occurred after 11:00 LT. Accompanied to NPF events were low concentrations of VOCs and high concentrations of O3. The undefined events by NUC or AIT were associated with the upwind transport of newly formed particles. Source apportionment analysis suggested that NPF and undefined events were the largest contributor to NNUC (51 ± 28 %), NAIT (41 ± 26 %), and NUFP (45 ± 27 %), while coal combustion and biomass burning, and traffic emission were the second largest contributor to NNUC (22 ± 20 %) and NAIT (39 ± 28 %), respectively.

Effects of the test aerosol on the performance of periodic technical inspection particle counters

A new scheme for periodical technical inspection (PTI) of diesel-engine exhaust based on the measurement of particle number (PN) concentration was recently introduced in several European countries. PN concentration is measured directly at the tailpipe using portable particle counters known as PN-PTI. The technical specifications of these instruments are defined at a national level, and the type-examination and verification procedures differ considerably among European countries. In this study, we examined how the choice of test aerosol can affect the counting efficiency profile of the PN-PTI sensors, the majority of which are based on diffusion charging (DC). Carbonaceous aerosols were produced by combustion and spark discharge generators, sodium chloride (NaCl) particles were generated from aqueous solutions using several commercially available nebulizers and silver particles were produced by a silver particle generator. In most cases, the response of DC-based sensors depended strongly on the morphology of the test particles. Comparison with a Euro 3 diesel engine without a diesel particle filter (DPF) indicated that the combustion aerosols generated by combustion generators were the best proxy for soot emitted by diesel vehicle engines. On the contrary, the use of NaCl and spark discharge particles as test aerosols led in some cases to an over- or underestimation of the PN concentration by up to about a factor of two. Moreover, our results showed that the response of each type of DC-based sensors is individual and, as a result, it is impossible to determine a generally applicable factor to correct for the impact of the test aerosol properties. We recommend that the verification of PN-PTI instruments be preferably performed with soot particles produced by a combustion generator (identical or similar to the one used during the type-examination) in order to avoid corrections for the impact of the material on the response of the instruments.

Particle Number Concentration Measurements on Public Transport in Bangkok, Thailand.

Traffic is a major source of particulate pollution in large cities, and particulate matter (PM) level in Bangkok often exceeds the World Health Organisation limits. While PM2.5 and PM10 are both measured in Bangkok regularly, the sub-micron range of PM, of specific interest in regard to possible adverse health effects, is very limited. In the study, particle number concentration (PNC) was measured on public transport in Bangkok. A travel route through Bangkok using the state railway, the mass rapid transport underground system, the Bangkok Mass Transit System (BTS) Skytrain and public buses on the road network, with walking routes between, was taken whilst measuring particle levels with a hand-held concentration particle counter. The route was repeated 19 times covering different seasons during either morning or evening rush hours. The highest particle concentrations were found on the state railway, followed by the bus, the BTS Skytrain and the MRT underground with measured peaks of 350,000, 330,000, 33,000 and 9000 cm-3, respectively, though particle numbers over 100,000 cm-3 may be an underestimation due to undercounting in the instrument. Inside each form of public transport, particle numbers would peak when stopping to collect passengers (doors opening) and decay with a half-life between 2 and 3 min. There was a weak correlation between particle concentration on bus, train and BTS and Skytrain with carbon monoxide concentration, as measured at a fixed location in the city.

Design and evaluation of a volatile particle remover combining hot dilution and a thermodenuder

Portable and efficient removal of volatile particles from motor vehicle exhaust is essential for the accurate measurement of involatile solid particle number concentration in on-board emission measurement systems. For this purpose, a volatile particle remover with a combination of hot dilution and a thermodenuder (referred to as VPR-TD) was designed. The flow and temperature fields of the VPR-TD were simulated and analyzed by COMSOL Multiphysics software by which experimental verification and system performance tests were performed. The simulation showed that the effective heating length and residence time of the VPR-TD increased by 6 cm and 25%, respectively, as the dilution ratio increased from 1 to 10 at a total flow of 0.6 L/min at 350 °C. In addition, the experimental results showed that the penetration efficiency of 100 nm sodium chloride (non-volatile particles) in the VPR-TD was higher than 70.4%, and the removal efficiency of 30 nm tetracontane (volatile particles) was higher than 99% at a total flow 0.6 L/min, heating temperature 350 °C, and dilution ratios of 5 and 10. In summary, when the dilution ratio was set to 10, the device met the requirements of the Light Duty Vehicle Emission Limits and Measurement Methods (CHINA 6) for a volatile particle remover. At dilution ratio of 5, VPR-TD may be used as a pre-conditioning unit in portable emissions measurement systems.

International comparison CCQM-K150: particle number concentration (100 to 20 000 cm-3) and particle charge concentration (0.15 to 3 fC cm-3)

Main textThis report presents the results of CCQM-K150, a key comparison between nine National Measurement Institutes (NMIs) which tested the capability of the NMIs to measure particle number concentration (in the range of 100 to 20 000 cm-3) using condensation particle counters (CPCs), and particle charge concentration (in the range of 0.15 to 3 fC cm-3) using aerosol electrometers (AEs).Measurements of aerosol particle number concentration are needed to demonstrate compliance to vehicle emission legislation and are becoming increasingly important in other areas such as ambient air and workplace monitoring. The measurements are typically carried out using condensation particle counters, which are calibrated using either reference CPCs or reference AEs.An analogous report is available for the CCQM-P189 comparison. CCQM-P189 was identical to and used the same experimental data as CCQM-K150 with one exception: data from TROPOS, which is not an NMI or Designated Institute (DI), were only included in CCQM-P189.CCQM-K150 was an amount-of-substance Track C comparison.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).