Total Surface Area Concentrations Research Articles

A method to obtain scattering phase function based on particle size distribution and refractive index retrieved from Aurora 4000 multi-angle scattering measurements: A numerical study

Scattering phase function of aerosol particles is crucial to the accurate estimation of aerosol direct radiative forcing, and is also of great interest in the field of remote sensing. One feasible and promising way to obtain scattering phase function on a long-term scale with satisfying temporal resolution is based upon the particle size distribution (PSD) and the refractive index (m = n + ik) simultaneously retrieved from multi-wavelength multi-angle scattering detected by Aurora 4000, a commercially available and easily operated, as well as lab- and field-deployable instrument. In this study, a retrieval algorithm was specifically developed according to the characteristics of Aurora 4000 measurements, using the regularization method. The algorithm was systematically evaluated for its applicability, capability and limitation by a series of designed numerical experiments, considering both monomodal and bimodal log-normal distributions with various settings of parameters and different m, in order to be prepared for its application in field studies. The retrieval algorithm has exhibited a successful performance in deriving the PSDs and the real part of the refractive index (n) without a priori assumptions about the shape of the PSDs and the value of n, and consequently in obtaining scattering phase function, for aerosol particles from purely scattering to slightly absorbing (the imaginary part of the refractive index k ≤ 0.01) both without and with assumed measurement errors (when ±ψs≤±3%). Under such circumstances, relative errors in retrieved effective diameter (De), total surface area concentration (Sa), total volume concentration (Va) are almost within ±20%, relative errors in retrieved total number concentration (Na) stay roughly within ±50%, and absolute errors of n are well within ±0.02. Moreover, relative errors in backscattering ratio (BSR) and the defined parameter to describe relative errors in scattering phase function (δP), as good indicators for demonstrating how well scattering phase function can be captured, averagely locate within ±20% and ±10%, respectively. In contrast, relative errors in the widely used parameters of the asymmetry parameter (g) and hemispheric backscattering ratio (HBSR) remain still quite small even when considerable deviations can be observed in the forward and backward scattering regimes. Hopefully, when applied in field studies in the next step, the retrieval algorithm established in this study will improve our knowledge and understanding on angular scattering properties of ambient aerosol particles, as well as the associated impacts on aerosol direct radiative forcing.

Reducing the particles generated by flushing institutional toilets

Airborne particles play a significant role in the transmission of SARS-CoV-2, the virus that causes COVID-19. A previous study reported that institutional flush-O-meter (FOM) toilets can generate 3–12 times as many droplets as other toilets by splashing (large droplets) and bubble bursting (fine droplets). In this study, an aerosol suppression lid was evaluated to measure the reduction of particles by size using three metrics; number, surface area, and mass concentrations. To quantify toilet flush aerosol over time, detailed particle size distributions (from 0.016–19.81 µm across 152 size bins) were measured from a FOM toilet in a controlled-environment test chamber, without ventilation, with and without use of the suppression lid. Prior to each flushing trial, the toilet bowl water was seeded with 480 mL fluorescein at 10 mg/mL. A high-speed camera was used to record the large droplet movements after flushing. An ultraviolet-visible spectrophotometer was used to analyze the wipe samples to evaluate the contamination on the lid. The particle number, surface area, and mass concentrations without a lid were elevated compared to a lid in the first 90 sec. Overall, the lid reduced 48% of total number concentration, 76% of total surface area concentration, and 66% of total mass concentration, respectively. Depending on the particle size, the number concentration reduction percentage ranged from 48–100% for particles larger than 0.1 µm. Large droplets created by splashing were captured by the high-speed camera. Similar studies can be used for future particle aerodynamic studies. The fluorescein droplets deposited on the lid back sections, which were closer to the FOM accounted for 82% of the total fluorescein. Based on two-way ANOVA analysis, there were significant differences among both the experimental flushes (p = 0.0185) and the sections on the lid (p = 0.0146). Future work should explore the aerosolization produced by flushing and the performance of the lid in real restroom environments, where feces and urine exist in the bowl water and the indoor ventilation system is in operation.

P.857Cognitive reserve in child and adolescent offspring of patients diagnosed with schizophrenia or bipolar disorder

This study was conducted to investigate PM emissions and performance of SI engines fueled with butanol-methanol-gasoline during air dilution operation. Iso-butanol and methanol were blended with gasoline at volume concentrations of up to 40% (10, 20 vol% iso-butanol and methanol, respectively). The effects of lean mixture on engine performance and PM emissions with blends were investigated to find that the power performance of blended fuels is comparable to that of gasoline. High-proportion blends also showed higher brake thermal efficiency (BTE) than gasoline. The brake specific fuel consumption (BSFC) of blends was also about 10% higher than that of gasoline under stoichiometric conditions; with a lean mixture, a reduction of about 9% in the BSFC of blends was observed. The combustion stability of the blends was reduced relative to that of gasoline. CO emissions from the blends decreased rapidly as the mixture became leaner. The NOx emissions of blended fuels were about 30–50% lower than that of gasoline (lambda >1.15) and decreased rapidly as the mixture grew leaner – a reduction of up to 80% was observed. However, when the excess air ratio was less than 1.15, the NOx emissions were about 30% higher than that of gasoline. The increasing BTE trend of blended fuels was similar to that of gasoline as the load increased. A significant reduction in PM concentration was observed during lean mixture operation, which was further reduced with blended fuels. Reduction of accumulation mode particle was more pronounced for blended fuels relative to nucleation mode particles. The total surface area concentration markedly decreased due to a reduction in particle diameter and total concentration. These results altogether suggest that lean mixture reduces PM emissions of blends and improves BTE; n-butanol/methanol addition also contributed to higher BTE and lower gaseous and PM emissions.

Particulate matter (PM) emissions and performance of bio-butanol-methanol-gasoline blends coupled with air dilution in SI engines

This study was conducted to investigate PM emissions and performance of SI engines fueled with butanol-methanol-gasoline during air dilution operation. Iso-butanol and methanol were blended with gasoline at volume concentrations of up to 40% (10, 20 vol% iso-butanol and methanol, respectively). The effects of lean mixture on engine performance and PM emissions with blends were investigated to find that the power performance of blended fuels is comparable to that of gasoline. High-proportion blends also showed higher brake thermal efficiency (BTE) than gasoline. The brake specific fuel consumption (BSFC) of blends was also about 10% higher than that of gasoline under stoichiometric conditions; with a lean mixture, a reduction of about 9% in the BSFC of blends was observed. The combustion stability of the blends was reduced relative to that of gasoline. CO emissions from the blends decreased rapidly as the mixture became leaner. The NOx emissions of blended fuels were about 30–50% lower than that of gasoline (lambda >1.15) and decreased rapidly as the mixture grew leaner – a reduction of up to 80% was observed. However, when the excess air ratio was less than 1.15, the NOx emissions were about 30% higher than that of gasoline. The increasing BTE trend of blended fuels was similar to that of gasoline as the load increased. A significant reduction in PM concentration was observed during lean mixture operation, which was further reduced with blended fuels. Reduction of accumulation mode particle was more pronounced for blended fuels relative to nucleation mode particles. The total surface area concentration markedly decreased due to a reduction in particle diameter and total concentration. These results altogether suggest that lean mixture reduces PM emissions of blends and improves BTE; n-butanol/methanol addition also contributed to higher BTE and lower gaseous and PM emissions.

Characterization of gaseous and particulate pollutants from gasification-based improved cookstoves

Cookstove studies have reported pollutant concentrations (mainly PM2.5, black carbon and CO) without routinely associating it with the design and operating principles of the stoves. Extensive characterization of pollutants from cookstoves and the effect of different operating conditions are required for a better understanding of the mechanisms of pollutant formation. In this study, a forced draft (FD) and a natural draft (ND) gasification-based improved cookstove were tested under controlled conditions. Real-time pollutant concentrations, both particulate (PM2.5, lung-deposited surface area and particle number size distribution) and gaseous (CO, CO2 and NOx), from these stoves using three types of fuel (applewood chips and chunks, cowdung cake and coal) along with different cookstove operating conditions (airflow rates and with or without a cooking pot) were measured and compared. The FD cookstove tended to exhibit higher concentrations of emissions compared to the ND cookstove. Increasing airflow through the FD stove decreased flame length and the residence time of VOCs inside the flame zone, which in turn increased pollutant concentrations. An optimum airflow producing the lowest particulate matter (PM) concentrations was established for the FD cookstove. The CO–CO2 ratio, an indicator of combustion efficiency, demonstrated strong correlations with PM2.5 (r=0.857), particle geometric mean diameter (r=0.900) and the total surface area concentration (r=0.908) indicating that CO–CO2 ratio may be used as a proxy for these PM metrics. Results reported in this study will facilitate further improvements in the design of future cookstoves.

Retrieval of aerosol parameters from multiwavelength lidar: investigation of the underlying inverse mathematical problem

We present an investigation of some important mathematical and numerical features related to the retrieval of microphysical parameters [complex refractive index, single-scattering albedo, effective radius, total number, surface area, and volume concentrations] of ambient aerosol particles using multiwavelength Raman or high-spectral-resolution lidar. Using simple examples, we prove the non-uniqueness of an inverse solution to be the major source of the retrieval difficulties. Some theoretically possible ways of partially compensating for these difficulties are offered. For instance, an increase in the variety of input data via combination of lidar and certain passive remote sensing instruments will be helpful to reduce the error of estimation of the complex refractive index. We also demonstrate a significant interference between Aitken and accumulation aerosol modes in our inversion algorithm, and confirm that the solutions can be better constrained by limiting the particle radii. Applying a combination of an analytical approach and numerical simulations, we explain the statistical behavior of the microphysical size parameters. We reveal and clarify why the total surface area concentration is consistent even in the presence of non-unique solution sets and is on average the most stable parameter to be estimated, as long as at least one extinction optical coefficient is employed. We find that for selected particle size distributions, the total surface area and volume concentrations can be quickly retrieved with fair precision using only single extinction coefficients in a simple arithmetical relationship.

Total Surface Area Concentration Measurements of Nanoparticles in Gases with an Electrical Sensor

AbstractNano‐objects with different chemical compositions and structures (shapes) are very important building blocks for nanostructured materials. The characterization of the nanoparticles in the gas phase during synthesis and their use is of great importance. The total nanoparticle surface area concentration is essential especially for describing interface processes, because of the increasing surface area per unit of mass with decreasing particle size. In this paper the possible use of an electrical sensor for measuring total surface area concentrations of spherical and agglomerated/aggregated nanoparticles in aerosols is discussed.

Evaluation of an electrical aerosol detector (EAD) for the aerosol integral parameter measurement

The performance of an electrical aerosol detector (EAD; TSI Model 3070A) was experimentally evaluated for measuring the integral parameters of particles (i.e., total length concentration of particles, and the total surface area concentrations of particles deposited in a human lung). The EAD consists of a unipolar diffusion charger with an ion trap, and aerosol electrometer. We first evaluated the performance of the EAD charger. Both polydisperse and monodisperse particles of Ag, NaCl, and oleic acid (with the dielectric constants of infinite, 6.1 and 2.5) were then generated to evaluate the particle material effect on the EAD readout.

Aerosol states in the free troposphere at northern midlatitudes

A statistical analysis of in situ observations of aerosols in the midlatitude free troposphere and tropopause region in summer is presented. Vertical profiles of the number density and the associated variability of nuclei mode and larger aerosol particles are discussed. These data confirm that the upper troposphere is an efficient net source region of new particles. Aerosols are studied by analyzing size‐segregated data, and it is suggested that observed extreme cases of aerosol evolution include a nucleation state, an accumulation state, and a cloud‐processed state. This interpretation implies that aerosol sources (nucleation from the gas phase) are closely tied to aerosol sinks (cloud scavenging of aerosol particles). Processes that could modify the proposed aerosol life cycle are discussed. Number size and surface area distributions typical for the various aerosol states are examined. The dry aerosol surface area ranges from 1 to 20 μm2 cm−3 in the free troposphere and from 2 to 13 μm2 cm−3 in the tropopause region. Parameterizations of the aerosol size distributions and total surface area concentrations are provided to facilitate the use of the data in atmospheric models.

Ash formation during fluidized-bed incineration of paper mill waste sludge

Ash formation during industrial-scale bubbling fluidized bed (BFB) and circulating fluidized-bed (CFB) combustion of bark, waste wood and paper mill sludges has been studied. The principal ash formation mechanism was the sintering of 0.2–4 μm paper filler mineral particles into larger, porous ash agglomerates from 10 to 200 μm in size which dominated the fly ash total mass and specific surface area. Fly ash total mass concentration at the electrostatic precipitator inlet conditions varied from 4.5 g N -1 m -3 at BFB to 8.3 g N -1 m -3 at CFB while the respective total surface area concentrations as determined with nitrogen absorption were 32 and 83 m 2 N -1 m -3. During bark combustion in the BFB, we observed an ultrafine mode at 0.05 μm consisting of spherical particles and their chain-type agglomerates. Ultrafine mode mass and surface area concentrations were 3 and 0.1 m 2 N -1 m -3, respectively, as determined with the electrical low-pressure impactor and with the differential mobility analyzer. Ultrafine particles were formed via nucleation of volatilized ash species followed by particle growth via collision and coalescence and via vapor condensation. During waste wood combustion in the CFB, ultrafine particle concentration was significantly lower than during bark combustion in BFB, indicating reduced ash volatilization during CFB combustion. When co-firing sludge with bark in the BFB and with waste wood in the CFB ultrafine particle concentration was further reduced. Results from continuous aerosol measurements by the electrical low-pressure impactor (ELPI), by the scanning differential mobility analyzer (SMPS) and by the tapered element oscillating microbalance (TEOM) as the function of BFB process conditions suggest that co-combustion of sludge reduces significantly the ultrafine particle formation rate. No significant enrichment of alkali and trace metals in the ultrafine particles was observed.