Peak Particle Number Concentration Research Articles

Observations of atmospheric new particle formation impacts on cloud condensation nuclei in summer at Mt.Tian

As one of the important sources of aerosols, new particle formation events can affect the spatiotemporal distribution of CCN. To analyze the characteristics of new particle formation (NPF) events and their effects on cloud condensation nuclei (CCN) during the summer at Mt.Tian, the data of aerosol size distribution and CCN number concentrations were measured using an aerosol wide-range particle size spectrometer and a cloud condensation nuclei counter from August 4 to 25, 2019, and combined with meteorological data and polycyclic aromatic hydrocarbons (PAHs) data. NPF events at Mt.Tian occurred seven days during the observation period, accounting for 32% of the observation days, and usually occurred at 13:00 and ended at 17:00 (Beijing Time, same below). NPF events particularly influenced the diurnal variations of aerosol number concentrations in different modes. The number concentrations of nucleation and Aitken modes increased rapidly while the accumulation mode increased slowly during 13:00 and 17:00 on NPF days. The peak particle number concentrations in the nucleation, Aitken and accumulation modes on NPF days were 5360.1 cm−3, 7185.6 cm−3 and 839.3 cm−3, respectively, which were 3.3, 1.8 and 1.7 times higher than those on non-NPF days during 13:00 and 17:00. The meteorological conditions of temperature higher than 20 °C, air pressure lower than 806 hPa, relative humidity (RH) lower than 40% and wind speed higher than 2.2 m s−1 are favorable for the occurrence of NPF events. The NPF events at Mt.Tian can impact the mass concentration of PAHs. More Fluoride (FL) and Phenanthrene (PHE) were generated on NPF days. The mass concentrations of FL and PHE on NPF days were 0.002 ± 0.003 ng m−3 and 0.020 ± 0.010 ng m−3, which were 243.54% and 28.44% higher than those on non-NPF days, respectively. NPF events were conducive to increased CCN concentration at Mt.Tian. After the NPF events, the mean number concentrations of CCN at each supersaturation (SS) on NPF days was about 20%–50% higher than on non-NPF days. The contribution of NPF events to the CCN number concentrations was 35.75%, 28.56%, 44.15%, 42.11% and 29.12% at 0.1%, 0.2%, 0.4%, 0.6% and 0.8% SS, respectively.

7 Construction and Characterization of a Thermal Spray Coating Aerosol Generator

Abstract Thermal spray coating (TSC) is a surface treatment process whereby feedstock material is sprayed onto surfaces under pressure where it solidifies and forms a solid coating. In metal TSC processes, large quantities of aerosols, including fine and ultrafine metal particles are generated. However, exposure assessment for TSC is lacking. The goal of this study was to construct a TSC aerosol generation system and to characterize the physicochemical properties of aerosols generated during coating processes. A computer-controlled, automated electric arc wire-TSC aerosol generator system was built in an enclosed room, where a rotary motor rotates a metal feedstock pipe in circular and up-and-down directions to allow even deposition of coating material on the pipe surface. The characteristics of aerosolized particles during spray coating using a stainless-steel wire (PMET 720) showed that: 1) respirable mass concentrations ranged from 142–218 mg/m3 (3 spray shots with each shot of 1-sec during 20-min sampling), 2) diameter of peak particle number concentrations was between 360 nm and 400 nm, 3) mass median aerodynamic diameter determined by an impactor ranged from 290–370 nm, 4) particle morphology was observed to be diverse including chain-like agglomerates and spherical and cylinder-like shapes, and 5) metal composition was 80% iron, 17% chromium, and 3% manganese with trace amounts of nickel and copper. These findings are limited to one wire type and suggests the need for further investigations evaluating various parameters (e.g., wire/powder types, high/low energy, ventilation on/off) to obtain emission rates and recommend control measures.

Spatial distributions of particle number size distributions generated during cooking processes and the impacts of range hoods

Cooking oil fume (COF) is associated with an increased risk of health effects. The particle number size distribution (PNSD) of COF presenting as lognormal structures is recognized as a key metric in determining its exposure toxicities, but the information of its spatial distributions and impacting factors are still lacking. This study conducted real-time monitoring COF PNSD during the cooking processes in a kitchen laboratory. Results showed that COF PNSD presented as a combination of two lognormal distributions. The peak diameters of PNSD inside the kitchen were: 385 nm (very close to the source), 126 nm (5 cm above the source), 85 nm (10 cm above the source) to 36 nm (breath point, 50 cm above the source), 33 nm (sucking surface of the ventilation hood), 31 nm (1 m horizontally to the source), and 29 nm (3.5 m horizontally to the source). The reasons of this observation was the sharp decrease of temperature from the pot to the indoor environment reduced the surface partial pressure of the COF particles and caused a large amount of semi-volatile organic carbons (SVOCs) with lower saturation ratios condensed on the COF surface. With the temperature difference became insignificant with the distance further to the source, the reduction of the supersaturation helped the gasification of these SVOCs. Dispersion led to a linearly horizontal decreases ((1.85 ± 0.10) × 106#/cm3/m) in particle numbers with further distances, making the peak particle number concentrations decrease from 3.5 × 105#/cm3 at the breath point to 1.1 × 105#/cm3 at the point 3.5 m to the source. Cooking dishes also presented as mode diameters of 22-32 nm at the breath point. The amount of edible oil used in different dishes is positively correlated with the peak concentration of COF. Only increasing the exhaust force of the range hood cannot significantly change the sucked COF particle numbers and sizes, owning to that COF particles are mainly small sizes. New technologies on cleaning small size particles and efficient supplemental air should be given more considerations.

Particle dispersion and removal associated with kitchen range hood and whole house ventilation system

The objective of this study is to evaluate how the removal and dispersion of the cooking-generated particles in a residential unit vary with ventilation strategies. Computational fluid dynamics (CFD) simulations were performed to evaluate the particle removal and dispersion performance of six ventilation strategies with three make-up air supply scenarios and two kitchen range hood designs. The results showed that the particle capture efficiency ranged from 0.58 to 1.00 for 2.5 μm particles, and from 0.62 to 0.96 for 10 μm particles depending on the ventilation strategies. The peak particle number concentration of the breathing zone in the kitchen was the lowest when supplying the make-up air from the whole house ventilation system, which was only 0.07% of the peak concentration with supplying natural make-up air through a kitchen window. When using the make-up air from the whole house ventilation system, 1-h integrated exposure was decreased by 92.1% for the kitchen, 89.4% for the living room, and 98.7% for the bedroom, compared to the natural make-up air supply scenario. The results reveal that supplying make-up air from the living room and bedrooms while operating a typical range hood yields the largest particle removal, suggesting effective control of residential exposure to cooking-generated particles.

Size Distribution and Source Appointment of Road Particles During Winter in Tianjin

The significant role of traffic emissions mixed from various sources in urban air pollution has been widely recognized. However, the corresponding contributions to the roadside particle distribution are poorly understood due to the mixed impacts of various sources. Particle number concentrations of different sizes at the roadside in Nankai District of Tianjin were continuously monitored using a portable aerosol particle spectrometer during the morning rush hour (07:30-09:20) from Nov. 9, 2018 to Jan. 6, 2019. Characteristic and influencing factors of particle size distributions were discussed combined with temperature and relative humidity data, while potential sources of particles at the roadside were identified based on size distribution analysis. The results showed that the average total particle number concentrations were 502 cm-3, and the concentrations of the accumulation mode and coarse mode were 500 cm-3 and 2 cm-3, respectively. The distribution of number concentrations at the roadside was unimodal and primarily concentrated at 0.25-0.50 μm, with peak sizes at 0.28-0.30 μm. The same distribution trend of particle number concentration and difference in the concentration in the same segment size were observed at different periods. Vehicle activity level was the main influencing factor of road particulate matter concentration on different weekdays; the probability of the high value of road particulate matter concentration was reduced by a reasonable combination of the vehicle tail numbers. Temperature and relative humidity were both found to be positively correlated with the number concentration of particles. With the increase in temperature and relative humidity, the total and peak particle number concentration showed an overall upward trend. In addition, the peak particle size increased from 0.28-0.30 μm to 0.35-0.40 μm when relative humidity was higher than 80%. Three sources, including road dust, brake and tire wear, and the aging particles from vehicle exhaust, were identified using positive matrix factorization in this study. Road dust contributed 8.6% of the total number concentration, which mainly consisted of particles with sizes above 5.00 μm. Brake and tire wear contributed 2.8% of the total number concentration of particles with a size range of 0.80-4.00 μm. The aging particles from vehicle exhaust contributed the most (88.5%), with a peak at 0.25-0.65 μm. The sources of roadside particles were mainly related to vehicle activity, whereas temperature and relative humidity also affected the particle number size distribution.

Sources of particle number concentration and noise near London Gatwick Airport.

There is increasing evidence of potential health impacts from both aircraft noise and aircraft-associated ultrafine particles (UFP). Measurements of noise and UFP are however scarce near airports and so their variability and relationship are not well understood. Particle number size distributions and noise levels were measured at two locations near Gatwick airport (UK) in 2018-19 with the aim to characterize particle number concentrations (PNC) and link PNC sources, especially UFP, with noise. Positive Matrix Factorization was used on particle number size distribution to identify these sources. Mean PNC (7500-12,000 p cm-3) were similar to those measured close to a highly trafficked road in central London. Peak PNC (94,000 p cm-3) were highest at the site closer to the runway. The airport source factor contributed 17% to the PNC at both sites and the concentrations were greatest when the respective sites were downwind of the runway. However, the main source of PNC was associated with traffic emissions. At both sites noise levels were above the recommendations by the WHO (World Health Organisation). Regression models of identified UFP sources and noise suggested that the largest source of noise (LAeq-1hr) above background was associated with sources of fresh traffic and urban UFP depending on the site. Noise and UFP correlations were moderate to low suggesting that UFP are unlikely to be an important confounder in epidemiological studies of aircraft noise and health. Correlations between UFP and noise were affected by meteorological factors, which need to be considered in studies of short-term associations between aircraft noise and health.

Effect of dimethoxymethane (DMM) additive on combustion and emission characteristics under different working conditions in CI engines

Dimethoxymethane (DMM) is considered a potential oxygenated fuel due to its high oxygen content (42.1%) and considerable heat value. However, little research emphasizes the impact of oxygenated fuels on small-particles (DP < 25 nm), which is harmful for human beings. In this investigation, the effect of DMM-diesel mixture on combustion and emission characteristics of a four-cylinder commercial CI engine is studied under normal working speeds and loads. Especially, the influence of DMM-diesel fuels on PMs included small-particles is analyzed comprehensively. The results show that the brake thermal efficiency (BTE) of DMM13 and DMM6.4 fuels increases by 1.06% and 0.4%, respectively, compared with that of D100 at the condition of 1400 rpm and 1.0 MPa. In terms of emission, the soot emission of DMM13 is reduced by 46% with respect to that of D100 at the condition of 0.6 MPa and 1400 rpm. Meanwhile, with the addition of DMM13, the peak particle number concentration (PNC) drops significantly, but increasing the proportion of small-particles. Moreover, the lowest total particle mass concentration (TPMC) is obtained as well. Substantially, DMM-diesel blends can realize the balance between low total particle number concentration (TPNC) and small geometric mean diameter (GMD).

The Influence of Graphene Oxide on Nanoparticle Emissions during Drilling of Graphene/Epoxy Carbon-Fiber Reinforced Engineered Nanomaterials

Graphene oxide (GO) nanoparticles are increasingly being used to tailor industrial composites. However, despite the advantages, GO has shown conceivable health risks and toxicity to humans and the environment if released. This study investigates the influence that GO concentrations have on nanoparticle emissions from epoxy-reinforced carbon fiber hybrid composites (EP/CF) during a lifecycle scenario, that is, a drilling process. The mechanical properties are investigated and an automated drilling methodology in which the background noise is eliminated is used for the nanoparticle emissions measurements. Real-time measurements are collected using a condensation particle counter (CPC), a scanning mobility particle sizer spectrometer (SMPS), a real-time fast mobility particle spectrometer (DMS50) and post-test analytical methods. The results observe that all three nanoparticle reinforced samples demonstrated a statistically significant difference of up to a 243% increase in mean peak particle number concentration in comparison to the EP/CF sample. The results offer a novel set of data comparing the nanoparticle release of GO with varying filler weight concentration and correlating it the mechanical influence of the fillers. The results show that the release characteristics and the influence in particle number concentration are primarily dependent on the matrix brittleness and not necessarily the filler weight concentration within the nanocomposite.

Effect of the pilot quantity on the ultrafine particle emissions and the combustion characteristics of a biodiesel pilot-ignited natural-gas dual-fuel engine

Natural gas has been widely utilized in urban transportation and power generation owing to its relatively low price and large abundance. One typical application of natural gas is as the primary fuel with dual-fuelling operation in compression ignition engines. In this study, biodiesel was used as the pilot fuel in a natural-gas dual-fuel engine, and the effect of the pilot quantity on the performance, the combustion and the emissions (especially the ultrafine particle emissions) were analysed. The test results show that, with increasing pilot quantity, the peak particle number concentration shifts from 29 nm to 100 nm while the peak particle mass concentration is stable and remains at 200 nm. Also, increasing the pilot quantity improves the brake’s thermal efficiency at low and medium loads, but this improvement is not obvious at high loads. With increasing pilot quantity, the first-stage heat release appears earlier and its peak value is also increased, accompanied by a decrease in the peak value of the second-stage heat release. The increase in the pilot quantity reduces the carbon monoxide emissions and the hydrocarbon emissions but increases the nitrogen oxide emissions. In comparison with the diesel pilot case, the size distribution of the ultrafine particle emissions from biodiesel pilot operation changes little, but both the number concentration and the mass concentration are reduced.

Prescribed burning of logging slash in the boreal forest of Finland: emissions and effects on meteorological quantities and soil properties

Abstract. A prescribed fire experiment was conducted on 26 June 2009 in Hyytiälä, Finland, to study aerosol and trace gas emissions from prescribed fires of slash fuels and the effects of fire on soil properties in a controlled environment. A 0.8 ha forest near the SMEAR II measurement station (Station for Measuring Ecosystem-Atmosphere Relations) was cut clear; some tree trunks, all tree tops and branches were left on the ground and burned. The amount of burned organic material was ~46.8 tons (i.e., ~60 tons ha−1). The flaming phase lasted 2 h 15 min, the smoldering phase 3 h. Measurements were conducted on the ground with both fixed and mobile instrumentation, and in the air from a research aircraft. In the middle of the burning area, CO2 concentration peaked around 2000–3000 ppm above the baseline, and peak vertical flow velocities were ~9 m s−1, as measured with a 10 Hz 3-D sonic anemometer placed within the burn area. In the mobile measurements the peak particle number concentrations were approximately 1–2 × 106 cm−3 in the plume at a distance of 100–200 m from the burn area. On the ground at the SMEAR II station the geometric mean diameter of the mode with the highest concentration was 80 ± 1 nm during the flaming phase and in the middle of the smoldering phase, but, at the end of the smoldering phase, the largest mode was 122 nm. In the volume size distributions, geometric mean diameter of the largest volume mode was 153 nm during the flaming phase and 300 nm during the smoldering phase. The lowest single-scattering albedo of the ground-level measurements was 0.7 in the flaming-phase plume and ~0.9 in the smoldering phase. Elevated concentrations of several volatile organic compounds (VOC) (including acetonitrile, a biomass burning marker) were observed in the smoke plume at ground level. Measurements at the forest floor (i.e., a richly organic layer of soil and debris, characteristic of forested land) showed that VOC fluxes were generally low and consisted mainly of monoterpenes, and VOC flux peaked after the burning. After one year, the fluxes had nearly stabilized close to the level before the burning. The clear-cutting and burning of slash increased the total long-term CO2 release from the soil, and altered the physical, chemical and biological properties of the soil, such as increased the available nitrogen contents of the soil, which in turn, affected the long-term fluxes of greenhouse gases.

Combustion and particle number emissions of a direct injection spark ignition engine operating on ethanol/gasoline and n-butanol/gasoline blends with exhaust gas recirculation

The combustion and particle number (PN) emissions of a direct injection spark ignition engine (DISI) operating on ethanol/gasoline and n-butanol/gasoline blends with exhaust gas recirculation (EGR) were studied in this paper. Firstly, the effect of EGR and fuel evaporation on charge cooling was investigated. The results indicate that both the addition of EGR and alcohol show evident charge cooling effect. The 0–10% mass fraction burned (MFB) combustion duration increases with increasing EGR rate and increasing charge cooling ability of fuels. As the EGR rate is increased from 0% to 20%, the 10–90% MFB combustion duration is prolonged by 25.5–38.9% for alcohol/gasoline blends, and 64.1% for gasoline. As alcohol is introduced, the 10–90% MFB combustion duration decreases. The addition of ethanol or n-butanol improves the combustion stability. The anti-knock ability mainly depends on the octane number and charge cooling effect of fuels, as well as EGR. Either ethanol/gasoline blends or EGR is beneficial to improve the anti-knock ability. However, n-butanol/gasoline blends show degraded anti-knock ability. Combined with EGR, it is possible to overcome the negative effect of n-butanol on knock. Furthermore, the effects of EGR rate and alcohol content on PN emissions were investigated. It is found that the peak particle number concentration gradually decreases and its distribution shifts toward smaller size with increasing EGR rate. Similarly, the increasing alcohol content in the blends results in decreased peak particle number concentration and higher proportion of finer particles.

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.

A mobile pollutant measurement laboratory—measuring gas phase and aerosol ambient concentrations with high spatial and temporal resolution

A mobile pollutant measurement laboratory was designed and built at the Paul Scherrer Institute (Switzerland) for the measurement of on-road ambient concentrations of a large set of trace gases and aerosol parameters with high time resolution (<15 s for most instruments), along with geographical and meteorological information. This approach allowed for pollutant level measurements both near traffic (e.g. in urban areas or on freeways/main roads) and at rural locations far away from traffic, within short periods of time and at different times of day and year. Such measurements were performed on a regular base during the project year of gas phase and aerosol measurements (YOGAM). This paper presents data measured in the Zürich (Switzerland) area on a late autumn day (6 November) in 2001. The local urban particle background easily reached 50 000 cm −3, with additional peak particle number concentrations of up to 400 000 cm −3. The regional background of the total particle number concentration was not found to significantly correlate with the distance to traffic and anthropogenic emissions of carbon monoxide and nitrogen oxides. On the other hand, this correlation was significant for the number concentration of particles in the size range 50–150 nm, indicating that the particle number concentration in this size range is a better traffic indicator than the total number concentration. Particle number size distribution measurements showed that daytime urban ambient air is dominated by high number concentrations of ultrafine particles (nanoparticles) with diameters <50 nm, which are immediately formed by traffic exhaust and thus belong to the primary emissions. However, significant variation of the nanoparticle mode was also observed in number size distributions measured in rural areas both at daytime and nighttime, suggesting that nanoparticles are not exclusively formed by primary traffic emissions. While urban daytime total number concentrations were increased by a factor of 10 compared to the nighttime background, corresponding factors for total surface area and total volume concentrations were 2 and 1.5, respectively.

Physical characteristics of Saharan dust near the Gulf of Guinea

The particle size, number and mass concentrations of Saharan dust during three successive Harmattan seasons in 1996, 1997 and 1998 in southern Ghana (6°40′N, 1°34′W) are reported. The transport distance for the dust was approximately 3000 km from the edge of the source region in the Sahara Desert and 150 km north of the Gulf of Guinea (5°N). The fluctuations in the physical characteristics of dust, in consonance with the seasonal migration of the Inter-tropical Discontinuity, are quantified. The peak particle number concentration recorded in 1997 (150 cm −3) is approximately two orders of magnitude greater than the minimum background aerosol concentration (1 cm −3). Average mass concentrations are calculated and evidence is provided that even at low latitudes and at great distances from the dust production zones, the Saharan dust influence on the particulate mass content of the atmosphere over West Africa is important. Aerosol mean diameters were 0.96, 1.16 and 1.02 μm for the 1996, 1997 and 1998 Harmattan seasons, respectively, with average mass concentrations reaching a peak of 134 μg m −3. In all cases, the mean aerosol diameter is observed to be smaller during the Harmattan period than during the rest of the year, an observation which is consistent with the transport of great quantities of small particles during the Harmattan season. It is shown that within the 1–5 μm diameter range, the Harmattan particle size distribution remains essentially stable regardless of the change in seasonal dust concentrations.