Effect of venting range hood flow rate on size-resolved ultrafine particle concentrations from gas stove cooking

Cooking is the main source of ultrafine particles (UFP) in homes. This study investigated the effect of venting range hood flow rate on size-resolved UFP concentrations from gas stove cooking. The same cooking protocol was conducted 60 times using three venting range hoods operated at six flow rates in twin research houses. Size-resolved particle (10–420?nm) concentrations were monitored using a NanoScan scanning mobility particle sizer (SMPS) from 15?min before cooking to 3?h after the cooking had stopped. Cooking increased the background total UFP number concentrations to 1.3?×?10³ particles/cm³ on average, with a mean exposure-relevant source strength of 1.8?×?10¹² particles/min. Total particle peak reductions ranged from 25% at the lowest fan flow rate of 36?L/s to 98% at the highest rate of 146?L/s. During the operation of a venting range hood, particle removal by deposition was less significant compared to the increasing air exchange rate driven by exhaust ventilation. Exposure to total particles due to cooking varied from 0.9 to 5.8?×?10⁴ particles/cm³·h, 3?h after cooking ended. Compared to the 36?L/s range hood, higher flow rates of 120 and 146?L/s reduced the first-hour post-cooking exposure by 76% and 85%, respectively.

© 2018 Crown Copyright. Published with license by Taylor & Francis Group, LLC     

Effects of Vehicle Cabin Filter Efficiency on Ultrafine Particle Concentration Ratios Measured In-Cabin and On-Roadway

Understanding the in-cabin microenvironment of vehicles is important for assessing human exposure to ultrafine particles (UFPs) of vehicular origin. Filtration through the cabin filter is one of the processes that determine the ratio of in-cabin to on-roadway (I/O) UFP concentrations. In this study, two filter test systems were used to measure the particle filtration efficiencies of fine, ultrafine, and coarse particles. Two types of particles (diesel exhaust UFPs and Arizona test particles) were used to represent the particle types expected in the on-roadway environment. The most penetrating particle size was around 300 nm with filtration efficiency lower than 20%. As the filter face velocity increased from 0.1 to 0.5 m s^?1, the filtration efficiency decreased by 10–20%. For vehicles that were frequently driven under heavy traffic conditions (65,000–72,000 vehicles day^?1) the pressure drop across the cabin filter increased up to 45 Pa within 10 months. It took 20 months to achieve the same pressure drop under moderate traffic conditions (10,000–24,000 vehicles day^?1) and 30 months under light conditions (700–2,000 vehicles day^?1). When the vehicle ventilation fan was on and the recirculation was off, it took approximately 10 months under heavy traffic conditions for UFP I/O ratios to increase by 40%. Explicit relationships between UFP I/O ratios and filter usage under various conditions were derived to facilitate cabin filter change decisions based on individual preferences.     

Corrosion studies with a new laboratory-scale system simulating large-scale diesel engines operating with residual fuels: Part II. Particle and deposit characteristics

Particle and deposit characteristics were studied with a new laboratory-scale deposition–corrosion apparatus designed to simulate the particle formation and deposition in large-scale diesel engines. Synthetic ash particles containing V, Ni, and Na are generated with an ultrasonic nebuliser. Total particle mass concentrations varied from 463 to 1739 mg/N m³ and highest concentrations were reached with SO₂(g) feed and cold dilution. Mass size distributions at the size range of 0.01–15 μm (aerodynamic size) were unimodal at 1.4 μm. Particle morphology changed dramatically from 1 to 5 μm sized solid particles without SO₂(g) feed into flat wet “pools” with SO₂(g) feed. It seemed that condensing sulphuric acid had dissolved the particles. Small 70–90 nm spherical particles were also observed with SO₂(g) feed. On the other hand, hardly any S was found in the deposits, which indicated that S as SO₂(g)/SO₃(g) was transported through the deposit pile into the base material.     

Preparation of Fe-Si Nanoparticles in Furnace Aerosol Reactor

Crystalline Fe-Si alloy particles ranging from 37 to 150 nm in diameter were produced by thermal decomposition of a mixture of Fe(CO)₅ and SiH₄ in a furnace aerosol reactor. The reactor was made of alumina, 2.4 cm in diameter and 100 cm in length. The operating variables were reactor temperature (800–1400°C), the Fe(CO)₅ concentration (2.5 × 10^?5 to 1.5 × 10^?4 moI/I), the molar ratio of Fe(CO)₅ to SiH₄ (100:0 to 50:50), and the residence time (2.5–10s). The primary particle size increased with reactor temperature increase and decreased when the Si content of the precursor was increased. The sintering of the particles within the agglomerates was an important factor in determining the primary particle size, and the sintering was inhibited by the silicon. The spatial variation of particle morphology was observed by in situ deposition of particles on a TEM grid. At 7 cm from the reactor inlet, nonagglomerated spherical particles encapsulating several smaller iron particles were found. The spherical structure were destroyed downstream to form agglomerates.     

Intra-Community Variability in Total Particle Number Concentrations in the San Pedro Harbor Area (Los Angeles,California)

Recent evidence links elevated ultrafine particle (UFP) concentrations with adverse health effects, but exposure assessments based upon PM _2.5 mass concentrations may be misleading. In order to better understand and quantify intra-community variability in UFP concentrations, a dense network of 14 monitoring sites was set-up in Los Angeles in two clusters—San Pedro/Wilmington and West Long Beach—in communities surrounding the Ports of Los Angeles and Long Beach. The network measured total particle number concentrations greater than 7 nm in diameter. In this range, UFP comprise approximately 90% of the total. Port-related activities—particularly goods movement associated with high volumes of heavy-duty diesel vehicle (HDDV) traffic—represent significant UFP sources. The field study was conducted from mid-February through mid-December 2007 to assess diurnal, seasonal, and spatial patterns and intra-community variability in total particle number concentrations. For sites within a few km of each other, simultaneous particle number concentrations can vary up to a factor of 10 (< 10,000 cm^?3 up to 90,000 cm^?3 for hourly averages calculated by month). The median hourly correlation coefficient (r) across all sites was modest and varied from 0.3 to 0.56. Specific site locations, particularly proximity to roadways used for goods movement, strongly affect observations. Clear diurnal and seasonal patterns are evident in the data. A diurnal pattern associated with high HDDV volumes and goods movement was identified. Coefficients of Divergence calculated for the site pairs suggest moderate heterogeneity overall (median study COD ≈ 0.35). The intra-urban variability observed in this study is comparable to and exceeds the inter-urban variability observed in a previous study in Los Angeles. UFP concentrations can vary considerably on short spatial scales in source-rich environments strongly influencing the accuracy of exposure assessments.     

Numerical Characterization of Particle Beam Collimation: Part II Integrated Aerodynamic-Lens–Nozzle System

As a sequel to our previous effort on the modeling of particle motion through a single lens or nozzle, flows of gas–particle suspensions through an integrated aerodynamic-lens–nozzle inlet have been investigated numerically. It is found that the inlet transmission efficiency (η_t) is unity for particles of intermediate diameters (D_p ～ 30–500 nm). The transmission efficiency gradually diminishes to ～40% for large particles (D_p > 2500 nm) because of impact losses on the surface of the first lens. There is a catastrophic reduction of η_t to almost zero for very small particles (D_p ≤ 15 nm) because these particles faithfully follow the final gas expansion. We found that, for very small particles, particle transmission is mainly controlled by nozzle geometry and operating conditions. A lower upstream pressure or a small inlet can be used to improve transmission of very small particles, but at the expense of sampling rate, or vice versa. Brownian motion exacerbates the catastrophic reduction in η_t for small particles; we found that the overall particle transmission efficiency can be roughly calculated as the product of the aerodynamic and the purely Brownian efficiencies. For particles of intermediate diameters, Brownian motion is irrelevant, and the modeling results show that the transmission efficiency is mainly controlled by the lenses. Results for an isolated lens or nozzle are used to provide guidance for the design of alternative inlets. Several examples are given, in which it is shown that one can configure the inlet to preferentially sample large particles (with η_t > 50% for D_p = 50–2000 nm) or ultrafine particles (with η_t > 50% for D_p = 20–1000 nm). Some of the results have been compared with experimental data, and reasonable agreement has been demonstrated.     

Aerosol Development and Interaction in an Urban Plume

Wintertime measurements of atmospheric aerosol over the size range 3-500 nm made approximately 30 m above street level in central Manchester are reported. These are compared with measurements of trace gases. It is found that secondary accumulation mode particles follow closely the values of NO_x in the atmosphere and are closely related to vehicle activity, reaching a maximum at about 9 am. New particle formation close to the observation point is closely related to SO₂ concentrations, predominately during daylight hours, and is a maximum around mid-day but persists after dark. The concentrations of fine and Aitken mode particles were much higher than in nearby rural areas, but the concentration of particles in the size range 200-500 nm were similar at the urban and rural sites. In addition, measurements of ammonia, a gas often important in nucleation kinetics, revealed concentrations up to 17 ppb in Manchester.     

Axial and radial CO concentration profiles in an atmospheric bubbling FB combustor

Atmospheric Bubbling Fluidised Bed Combustion (ABFBC) of a bituminous coal and anthracite with particle diameters in the range 500-4000 μm was investigated in a pilot-plant facility (circular section with 0.25 m internal diameter and 3 m height). The experiments were conducted at steady-state conditions using three excess air levels (10, 25 and 50%) and bed temperatures in the 750-900 °C range. Combustion air was staged, with primary air accounting for 100, 80 and 60% of total combustion air. The effect of limestone addition was also tested.Large CO concentrations were observed inside the bed, up to 8 and 6% (v/v) in the cases of anthracite and bituminous coals, respectively. These concentrations decreased sharply as the gases emerged from the bed, and the CO flue gas concentration observed was in general less than 2000 and 4000 ppm, respectively. The CO flue gas concentration increased with air staging and with limestone addition, but decreased with either excess air or temperature increase. The observed results confirm the influence of sand particles (and probably of SO₂) in the ‘quenching’ of the oxygenated free radicals (HO and HO₂) reactions responsible for the CO oxidation inside the bed.     

Investigation of vehicle exhaust sub-23 nm particle emissions

A solid particle number limit was applied to the European legislation for diesel vehicles in 2011. Extension to gasoline direct injection vehicles raised concerns because many studies found particles below the lower size limit of the method (23 nm). Here we investigated experimentally the feasibility of lowering this size. A nano condensation nucleus counter system (nCNC) (d_50% = 1.3 nm) was used in parallel with condensation particle counters (CPCs) (d_50% = 3 nm, 10 nm and 23 nm) at various sampling systems based on ejector or rotating disk diluters and having thermal pre-treatment systems consisting of evaporation tubes or catalytic strippers. An engine exhaust particle sizer (EEPS) measured the particle size distributions. Depending on the losses and thermal pre-treatment of the sampling system, differences of up to 150% could be seen on the final detected particle concentrations when including the particles smaller than 23 nm in diameter. A volatile artefact as particles with diameters below 10 nm was at times observed during the cold start measurements of a 2-stroke moped. The diesel vehicles equipped with the Diesel Particulate Filter (DPF) had a low solid sub-23 nm particles fraction (<20%), the gasoline with direct injection vehicles had higher (35–50%), the gasoline vehicles with port fuel injection and the two mopeds (two and four-stroke) had the majority of particles below 23 nm. The size distributions peaked at 60–80 nm for the DPF equipped vehicles, at 40–90 nm for the gasoline vehicles with a separate nucleation mode peak at approximately 10 nm sometimes. Mopeds peaked at sizes below 50 nm when their aerosol was thermally pre-treated.

© 2017 American Association for Aerosol Research     

A Laboratory Comparison of Real-Time Measurement Methods for 10–100-nm Particle Size Distributions

We present information regarding the relative performance of five TSI particle sizing instruments when presented with several log-normally distributed particle populations that vary in terms of composition, concentration, and modal mean diameter (in the range of 10–100 nm) in a controlled laboratory environment. In experiments conducted with NaCl, NaNO₃, and organic aerosols, across a total particle concentration suite ranging from approximately 1 × 10⁴ cm^?3 to 1 × 10⁶ cm^?3, total number concentrations of sub-100-nm diameter particles from four SMPS systems and an FMPS all fall within ±50% of each other (and generally are within ±30%). However, larger discrepancies are evident in the particle size distribution, particularly for the NaCl particles, with an SMPS operated with a water-based CPC exhibiting large negative bias in modal peak concentrations relative to the isobutanol-based SMPS systems and the FMPS. Much closer agreement is found for NaNO₃ particles, although the SMPS systems tended to exhibit higher modal peak concentrations, and a slight shifting toward lower modal peak diameter than the FMPS.

Copyright 2014 American Association for Aerosol Research     

First measurements of the number size distribution of 1–2 nm aerosol particles released from manufacturing processes in a cleanroom environment

This study was conducted to observe a potential formation and/or release of aerosol particles related to manufacturing processes inside a cleanroom. We introduce a novel technique to monitor airborne sub 2 nm particles in the cleanroom and present results from a measurement campaign during which the total particle number concentration (>1 nm and >7 nm) and the size resolved concentration in the 1 to 2 nm size range were measured. Measurements were carried out in locations where atomic layer deposition (ALD), sputtering, and lithography processes were conducted, with a wide variety of starting materials. During our campaign in the clean room, we observed several time periods when the particle number concentration was 10⁵ cm^?3 in the sub 2 nm size range and 10⁴ cm^?3 in the size class larger than 7 nm in one of the sampling locations. The highest concentrations were related to the maintenance processes of the manufacturing machines, which were conducted regularly in that specific location. Our measurements show that around 500 cm^?3 sub 2 nm particles or clusters were in practice always present in this specific cleanroom, while the concentration of particles larger than 2 nm was less than 2 cm^?3. During active processes, the concentrations of sub 2 nm particles could rise to over 10⁵ cm^?3 due to an active new particle formation. The new particle formation was most likely induced by a combination of the supersaturated vapors, released from the machines, and the very low existing condensation sink, leading to pretty high formation rates J_{1.4 nm} = (9 ± 4) cm^?3 s^?1 and growth rates of particles (GR_{1.1–1.3 nm} = (6 ± 3) nm/h and GR_{1.3–1.8 nm} = (14 ± 3) nm/h).

Copyright © 2017 American Association for Aerosol Research     

Synthesis of CaCu3Ti4O12 Micron-cubes and rods via high proportion molten salt method

CaCu₃Ti₄O₁₂ (CCTO) particles were produced from a CuO–CaCO₃–TiO₂ peroxo-hydroxide precursor material in NaCl–KCl and Na₂SO₄–K₂SO₄ salt mixtures via the molten-salt synthesis method at different salt-to-precursor mass ratios. Regular-shaped CCTO particles of cubes, rods, and polyhedrons can be obtained at large salt-to-precursor mass ratios of above 50:1. With the extension of sintering time, the particle shape is more regular and the size is larger. Long micro rods with a length of about 53 μm can be obtained at a mass ratio of 125:1 and a long sintering time of 72 h in sulfate salts. The formation mechanisms are also discussed and the results suggest that a large salt-to-precursor mass ratio may provide a sufficient number of Na − K ions to sufficiently modify the particle shape and form regular-shaped cubes and rod-like particles. At the same time, CCTO ceramics synthesized by Na₂SO₄–K₂SO₄ molten-salt method show good dielectric properties, with a dielectric constant higher than 10⁴ and a loss factor less than 0.45 in the range of 20 Hz to 1 MHz.     

CO adsorption energy on planar Au/TiO2 model catalysts under catalytically relevant conditions

The adsorption of CO on planar Au/TiO₂ model catalysts was studied by polarization-modulation infrared reflection–absorption spectroscopy (PM-IRAS) under catalytically relevant pressure (10–50 mbar) and temperature (30–120 °C) conditions, both in pure CO and in CO/O₂ reaction gas mixtures. The adsorption energy of CO on the Au particles was determined by a quantitative analysis of the temperature dependence of the CO absorption intensity in adsorption isobars. The data reveal considerable effects of the Au particle size when pure CO is used; the initial adsorption energy decreases from 74 kJ mol⁻¹ (2 nm mean Au particle diameter) to 62 kJ mol⁻¹ (4 nm). For CO/O₂ gas mixtures, the initial CO adsorption energy is, irrespective of the Au particle size, constant at 63 kJ mol⁻¹ (i.e., the CO adsorption energy is reduced for smaller Au particles), but this effect vanishes for larger Au particles.     

AEROSOL DYNAMICS

ABSTRACT

Photodetector pulse heights from an ultrafine condensation nucleus counter increase monotonically with particle size in the ～ 2.7–15 nm diameter range. This relationship can be used to measure concentrations and size distributions of ultrafine aerosols. In this study, we investigated the sensitivity of size-dependent pulse heights to total particle concentration, absolute pressure (0.25–1 atmosphere), and particle composition (H₂SO₄, (NH₄)2SO₄, NaCl, and tungsten oxide). We found that pulse heights shifted significantly with pressure and slightly with concentration. Coincidence led to errors for concentrations exceeding 4 × 10³ cm^?3. Over the range of conditions investigated, however, the observed shifts in the pulse height voltage were independent of size. The pulse height method is particularly applicable to situations involving low ultrafine particle concentrations, such as are encountered in the remote troposphere.     

New Particle Formation and Growth in an Isoprene-Dominated Ozark Forest: From Sub-5 nm to CCN-Active Sizes

Particle Investigations at a Northern Ozarks Tower: NOx, Oxidant, Isoprene Research (PINOT NOIR) were conducted in a Missouri forest dominated by isoprene emissions from May to October 2012. This study presents results of new particle formation (NPF) and the growth of new particles to cloud condensation nuclei (CCN)-active sizes (～100 nm) observed during this field campaign. The measured sub-5 nm particles were up to ～20,000 cm^?3 during a typical NPF event. Nucleation rates J₁ were relatively high (11.0 ± 10.6 cm^?3 s^?1), and one order of magnitude higher than formation rates of 5 nm particles (J₅). Sub-5 nm particle formation events were observed during 64% of measurement days, with a high preference in biogenic volatile organic compounds (BVOCs)- and SO₂-poor northwesterly (90%) air masses than in BVOCs-rich southerly air masses (13%). About 80% of sub-5 nm particle events led to the further growth. While high temperatures and high aerosol loadings in the southerly air masses were not favorable for nucleation, high BVOCs in the southerly air masses facilitated the growth of new particles to CCN-active sizes. In overall, 0.4–9.4% of the sub-5 nm particles grew to CCN-active sizes within each single NPF event. During a regional NPF event period that took place consecutively over several days, concentrations of CCN size particles increased by a factor of 4.7 in average. This enhanced production of CCN particles from new particles was commonly observed during all 13 regional NPF events during the campaign period.

Copyright 2014 American Association for Aerosol Research     

Ultrafine particle penetration through idealized vehicle cracks

Understanding the in-cabin microenvironment of vehicles is important for assessing human exposure to ultrafine particles (UFPs, diameter <100 nm) of vehicular origin. UFP penetration through cracks on the vehicle envelope is one of the influencing processes that determine the in-cabin UFP concentrations. In this study, penetration factors, calculated as the ratio of the downstream to upstream UFP concentrations across seven idealized cracks, were characterized for different crack sizes under a range of different pressure drops across the cracks. Three types of UFPs (neutralized diesel exhaust particles, unneutralized diesel exhaust particles, and vehicle exhaust particles) were used to investigate the effects of electric charge on penetration factors. Crack length, crack height, and pressure drop across the cracks account for approximately 10%, 5% and 12% of the penetration factor change, respectively. A coefficient “B”, which presents the ratio of the penetration factor for unneutralized to neutralized diesel particles, was introduced and successfully accounted for the electric charge effect on penetration factors.     

Controllable crystallite and particle sizes of WO3 particles prepared by a spray‐pyrolysis method and their photocatalytic activity

Information about correlation of material properties parameters (i.e., crystallite and particle sizes) and photocatalytic activity of tungsten trioxide (WO₃) particles are still lacking. For this reason, the purpose of this study was to synthesize WO₃ particles with controllable crystallite (from 18 to 50 nm) and particle sizes (from 58 to 677 nm) using a spray‐pyrolysis method and to investigate correlation of crystallite/particle size and photocatalytic activity. To gain control of crystallite/particle size, synthesis temperature (120–1300^°C) and initial precursor concentration (2.5–15 mmol/L) were investigated, which were then compared with the proposal of the particle formation mechanism. The results showed that both crystallite and particle sizes played an important role in photocatalytic activity. In this research, the optimum condition to produce the highest photocatalytic performance of WO₃ particles was at the temperature of 1200^°C (crystallite size: 25 nm), and initial concentration of 10 mmol/L (particle size: 105 nm). © 2013 American Institute of Chemical Engineers AIChE J, 60: 41–49, 2014     

Effects of water on the preparation,morphology, and properties of polyimide/silica nanocomposite films prepared by sol–gel process

Polyimide/silica (PI/SiO₂) nanocomposite films with 10 wt % of silica content were prepared by sol–gel process under the conditions with and without additional water. The presence of additional water has great effect on the silica particle size and thus on the properties of the prepared PI/SiO₂ films. The results indicated that with additional water, the silica particles formed before the imidization of poly(amic acid) (PAA) and aggregated with the increasing of temperature and degree of the proceeding imidization process. For the nonaqueous process, the hydrolysis condensation reaction of tetraethoxysilane (TEOS) did not occur until the imidization of PAA took place, and no silica particles were found in the unimidized PAA films. The hydrolysis–condensation reaction of TEOS was initiated simultaneously by the trace water released from the imidization reaction, the self‐catalysis mechanism of the approach provide a means of achieving uniformly dispersed silica particles formed in the PI matrix with particle size in the range of 30–70 nm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1579–1586, 2007     

Preparation and characterization of polyimide/silica‐barium titanate nanocomposites

The silica‐barium titanate (SiO₂‐BaTiO₃) nanocomposites coated with polyimide had been synthesized successfully by a dispersion polymerization method. The conformation, structure, and size of SiO₂‐BaTiO₃ nanocomposites coated with polyimide were investigated by using FT‐IR, EDAX, XRD,TEM, SEM, and TGA. The results indicate that there is a thin layer polymer of SiO₂‐BaTiO₃ nanocomposites surface, in which the polymer thickness is about 10 nm and the size of them are about 50–60 nm, and the particles are well‐dispersed with even particle size. In addition, the crystal structure of BaTiO₃ is stable in preparing composite process and the chemical bond is formed between the inorganic phase and the polymer matrix. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Dense CO2 antisolvent precipitation of levothyroxine sodium: A comparative study of GAS and ARISE techniques based on morphology and particle size distributions

Morphology and particle size distribution of levothyroxine sodium are experimentally investigated by comparing gas antisolvent (GAS) and atomized rapid injection for solvent extraction (ARISE) techniques using dense CO₂. Precipitation of levothyroxine sodium from ethanol was carried out at 25, 40 and 50 °C, with pressure in the 90–120 bar range and different concentrations of the organic solution. Particles produced by the GAS process are nanospheres whereas ARISE processed particles are either spherical or rod-like micro and nanoparticles. Particle size and size distributions of GAS processed levothyroxine sodium are in the 370–500 nm range, while the ARISE process produced particles in the 360–1200 nm range. In most cases, both techniques produced bimodal size distributions, due to particle agglomeration. The different morphological characteristics and particle size distributions of levothyroxine sodium obtained using GAS and ARISE at different operating conditions can be useful depending on the type of drug formulation chosen, as well as the route of drug administration and delivery system.