scholarly journals Distribution of non-spherical nanoparticles in turbulent flow of ventilation chamber considering fluctuating particle number density

2021 ◽  
Vol 42 (3) ◽  
pp. 317-330
Author(s):  
Ruifang Shi ◽  
Jianzhong Lin ◽  
Hailin Yang ◽  
Mingzhou Yu
Keyword(s):  
Turbulent Flow ◽  
Particle Number ◽  
Geometric Mean ◽  
Particle Diameter ◽  
Number Concentration ◽  
Particle Number Concentration ◽  
Initial Particle ◽  
Coagulation Rate ◽  
Proposed Model ◽  
Mean Concentration

AbstractThe Reynolds-averaged general dynamic equation (RAGDE) for the nanoparticle size distribution function is derived, including the contribution to particle coagulation resulting from the fluctuating concentration. The equation together with that of a turbulent gas flow is solved numerically in the turbulent flow of a ventilation chamber with a jet on the wall based on the proposed model relating the fluctuating coagulation to the gradient of mean concentration. Some results are compared with the experimental data. The results show that the proposed model relating the fluctuating coagulation to the gradient of mean concentration is reasonable, and it is necessary to consider the contribution to coagulation resulting from the fluctuating concentration in such a flow. The changes of the particle number concentration M0 and the geometric mean diameter dg are more obvious in the core area of the jet, but less obvious in other areas. With the increase in the initial particle number concentration m00, the values of M0 and the standard deviation of the particle size σ decrease, but the value of dg increases. The decrease in the initial particle diameter leads to the reduction of M0 and σ, and the increase in dg. With the increase in the Reynolds number, particles have few chances of collision, and hence the coagulation rate is reduced, leading to the increase in M0 and σ, and the decrease in dg.

scholarly journals Evolution of Aerosol Particles in the Rainfall Process via Method of Moments

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Fangyang Yuan ◽  
Fujun Gan
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Method Of Moments ◽  
Particle Number ◽  
Aerosol Particles ◽  
Geometric Mean ◽  
Number Concentration ◽  
Brownian Diffusion ◽  
Particle Number Concentration

The method of moments is employed to predict the evolution of aerosol particles in the rainfall process. To describe the dynamic properties of particle size distribution, the population balance equation is converted to moment equations by the method of moments and the converted equations are solved numerically. The variations of particle number concentration, geometric mean diameter, and geometric standard deviation are given in the cases that the Brownian diffusion and inertial impaction of particles dominate, respectively. The effects of raindrop size distribution on particle size distribution are analyzed in nine cases. The results show that the particle number concentration decreases as time goes by, and particles dominated by Brownian diffusion are removed more significantly. The particle number concentration decreases much more rapidly when particle geometric mean diameter is smaller, and the particle size distribution tends to be monodisperse. For the same water content, the raindrops with small geometric mean diameters can remove particles with much higher efficiency than those with large geometric mean diameters. Particles in the “Greenfield gap” are relatively difficult to scavenge, and a new method is needed to remove it from the air.

scholarly journals Urban Aerosol Particle Size Characterization in Eastern Mediterranean Conditions

Atmosphere ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 710 ◽  
Author(s):  
Hussein ◽  
Dada ◽  
Hakala ◽  
Petäjä ◽  
Kulmala
Keyword(s):  
Wind Speed ◽  
Particle Number ◽  
Early Stage ◽  
Eastern Mediterranean ◽  
Middle Eastern ◽  
Geometric Mean ◽  
Number Concentration ◽  
Effect Of Temperature ◽  
Particle Number Concentration ◽  
Weekly Cycle

Characterization of urban particle number size distribution (PNSD) has been rarely reported/performed in the Middle East. Therefore, we aimed at characterizing the PNSD (0.01–10 µm) in Amman as an example for an urban Middle Eastern environment. The daily mean submicron particle number concentration (PNSub) was 6.5 × 103–7.7 × 104 cm−3 and the monthly mean coarse mode particle number concentration (PNCoarse) was 0.9–3.8 cm−3 and both had distinguished seasonal variation. The PNSub also had a clear diurnal and weekly cycle with higher concentrations on workdays (Sunday–Thursday; over 3.3 × 104 cm−3) than on weekends (below 2.7 × 104 cm−3). The PNSub constitute of 93% ultrafine fraction (diameter < 100 nm). The mean particle number size distributions was characterized with four well-separated submicron modes (Dpg,I, Ni): nucleation (22 nm, 9.4 103 cm−3), Aitken (62 nm, 3.9 103 cm−3), accumulation (225 nm, 158 cm−3), and coarse (2.23 µm, 1.2 cm−3) in addition to a mode with small geometric mean diameter (GMD) that represented the early stage of new particle formation (NPF) events. The wind speed and temperature had major impacts on the concentrations. The PNCoarse had a U-shape with respect to wind speed and PNSub decreased with wind speed. The effect of temperature and relative humidity was complex and require further investigations.

scholarly journals Using non-negative matrix factorization for the identification of daily patterns of particulate air pollution in Beijing during 2004–2008

2012 ◽  
Vol 12 (5) ◽  
pp. 13015-13052 ◽  
Author(s):  
A. Thiem ◽  
U. Schlink ◽  
X.-C. Pan ◽  
M. Hu ◽  
A. Peters ◽  
...  
Keyword(s):  
Air Pollution ◽  
Matrix Factorization ◽  
Particle Number ◽  
Particle Diameter ◽  
Number Concentration ◽  
Particle Number Concentration ◽  
Concentration Data ◽  
Secondary Sources ◽  
Non Negative Matrix Factorization ◽  
Daily Patterns

Abstract. Increasing traffic density and a changing car fleet on the one hand as well as various reduction measures on the other hand may influence the composition of the particle population and, hence, the health risks for residents of megacities like Beijing. A suitable tool for identification and quantification of source group-related particle exposure compositions is desirable in order to derive optimal adaptation and reduction strategies and therefore, is presented in this paper. Particle number concentrations have been measured in high time- and space-resolution at an urban background monitoring site in Beijing, China, during 2004–2008. In this study a new pattern recognition procedure based on non-negative matrix factorization (NMF) was introduced to extract characteristic diurnal air pollution patterns of particle number and volume size distributions for the study period. Initialization and weighting strategies for NMF applications were carefully considered and a scaling procedure for ranking of obtained patterns was implemented. In order to account for varying particle sizes in the full diameter range [3 nm; 10 μm] two separate NMF applications (a) for diurnal particle number concentration data (NMF-N) and (b) volume concentration data (NMF-V) have been performed. Five particle number concentration-related NMF-N factors were assigned to patterns mainly describing the development of ultrafine (particle diameter Dp < 100 nm instead of DP) as well as fine particles (Dp < 2.5 μm), since absolute number concentrations are highest in these diameter ranges. The factors are classified into primary and secondary sources. Primary sources mostly involved anthropogenic emission sources such as traffic emissions or emissions of nearby industrial plants, whereas secondary sources involved new particle formation and accumulation (particle growth) processes. For the NMF-V application the five extracted factors mainly described coarse particle (2.5 μm < Dp < 10 μm) variations, generated by processes like dust storm events. Because particle volume depends on particle diameter in a cubic manner, larger particles are emphasized in the latter application. In order to gain insight in the day-by-day varying source-associated composition of the particle burden non-negative linear combinations of individual source-associated pollution patterns were used to approximate the original particle data. Consequently, this NMF-based procedure provides a reasonable numerical-statistical tool for the description of daily patterns of particle pollution, source identification and reconstruction of daily patterns by summarizing weighted factors.

scholarly journals Evolution of Combustion-Generated Particles at Tropospheric Conditions

2010 ◽  
Author(s):  
Kathleen M. Tacina ◽  
Christopher M. Heath
Keyword(s):  
Count Data ◽  
Particle Number ◽  
Jet Fuel ◽  
Number Concentration ◽  
Particle Number Concentration ◽  
Initial Particle ◽  
Sampling System ◽  
Particle Count ◽  
Temperature And Pressure ◽  
Measured Particle

This paper describes particle evolution measurements taken in the Particulate Aerosol Laboratory (PAL). The PAL consists of a burner capable of burning jet fuel that exhausts into an altitude chamber that can simulate temperature and pressure conditions up to 13,700 m. After presenting results from initial temperature distributions inside the chamber, particle count data measured in the altitude chamber are shown. Initial particle count data show that the sampling system can have a significant effect on the measured particle distribution: both the value of particle number concentration and the shape of the radial distribution of the particle number concentration depend on whether the measurement probe is heated or unheated.

Impact of Urban Pollution on Organic-Mediated New-Particle Formation and Particle Number Concentration in the Amazon Rainforest

2021 ◽  
Vol 55 (8) ◽  
pp. 4357-4367
Author(s):  
Bin Zhao ◽  
Jerome D. Fast ◽  
Neil M. Donahue ◽  
Manish Shrivastava ◽  
Meredith Schervish ◽  
...  
Keyword(s):  
Particle Number ◽  
Urban Pollution ◽  
Particle Formation ◽  
Number Concentration ◽  
Amazon Rainforest ◽  
Particle Number Concentration ◽  
New Particle Formation

scholarly journals Modeling particle nucleation and growth over northern California during the 2010 CARES campaign

2015 ◽  
Vol 15 (21) ◽  
pp. 12283-12313 ◽  
Author(s):  
A. Lupascu ◽  
R. Easter ◽  
R. Zaveri ◽  
M. Shrivastava ◽  
M. Pekour ◽  
...  
Keyword(s):  
Size Distribution ◽  
Particle Number ◽  
Particle Formation ◽  
Number Concentration ◽  
Aerosol Size Distribution ◽  
Particle Nucleation ◽  
Particle Number Concentration ◽  
New Particle Formation ◽  
Organic Vapors ◽  
Diurnal Variability

Abstract. Accurate representation of the aerosol lifecycle requires adequate modeling of the particle number concentration and size distribution in addition to their mass, which is often the focus of aerosol modeling studies. This paper compares particle number concentrations and size distributions as predicted by three empirical nucleation parameterizations in the Weather Research and Forecast coupled with chemistry (WRF-Chem) regional model using 20 discrete size bins ranging from 1 nm to 10 μm. Two of the parameterizations are based on H2SO4, while one is based on both H2SO4 and organic vapors. Budget diagnostic terms for transport, dry deposition, emissions, condensational growth, nucleation, and coagulation of aerosol particles have been added to the model and are used to analyze the differences in how the new particle formation parameterizations influence the evolving aerosol size distribution. The simulations are evaluated using measurements collected at surface sites and from a research aircraft during the Carbonaceous Aerosol and Radiative Effects Study (CARES) conducted in the vicinity of Sacramento, California. While all three parameterizations captured the temporal variation of the size distribution during observed nucleation events as well as the spatial variability in aerosol number, all overestimated by up to a factor of 2.5 the total particle number concentration for particle diameters greater than 10 nm. Using the budget diagnostic terms, we demonstrate that the combined H2SO4 and low-volatility organic vapor parameterization leads to a different diurnal variability of new particle formation and growth to larger sizes compared to the parameterizations based on only H2SO4. At the CARES urban ground site, peak nucleation rates are predicted to occur around 12:00 Pacific (local) standard time (PST) for the H2SO4 parameterizations, whereas the highest rates were predicted at 08:00 and 16:00 PST when low-volatility organic gases are included in the parameterization. This can be explained by higher anthropogenic emissions of organic vapors at these times as well as lower boundary-layer heights that reduce vertical mixing. The higher nucleation rates in the H2SO4-organic parameterization at these times were largely offset by losses due to coagulation. Despite the different budget terms for ultrafine particles, the 10–40 nm diameter particle number concentrations from all three parameterizations increased from 10:00 to 14:00 PST and then decreased later in the afternoon, consistent with changes in the observed size and number distribution. We found that newly formed particles could explain up to 20–30 % of predicted cloud condensation nuclei at 0.5 % supersaturation, depending on location and the specific nucleation parameterization. A sensitivity simulation using 12 discrete size bins ranging from 1 nm to 10 μm diameter gave a reasonable estimate of particle number and size distribution compared to the 20 size bin simulation, while reducing the associated computational cost by ~ 36 %.

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