scholarly journals Aerosol dynamics within and above forest in relation to turbulent transport and dry deposition

2015 ◽  
Vol 15 (14) ◽  
pp. 19367-19403 ◽  
Author(s):  
Ü. Rannik ◽  
L. Zhou ◽  
P. Zhou ◽  
R. Gierens ◽  
I. Mammarella ◽  
...  
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Time Scales ◽  
Atmospheric Chemistry ◽  
Dry Deposition ◽  
Particle Deposition ◽  
Vertical Transport ◽  
Forest Site ◽  
Aerosol Dynamics ◽  
The Impact

Abstract. One dimensional atmospheric boundary layer (ABL) model coupled with detailed atmospheric chemistry and aerosol dynamical model, the model SOSAA, was used to predict the ABL and detailed aerosol population (characterized by the number size distribution) time evolution. The model was applied over a period of ten days in May 2013 for a pine forest site in southern Finland. The period was characterized by frequent new particle formation events and simultaneous intensive aerosol transformation. Throughout this study we refer to nucleation, condensational growth and coagulation as aerosol dynamical processes, i.e. the processes that govern the particle size distribution evolution. The aim of the study was to analyze and quantify the role of aerosol and ABL dynamics in vertical transport of aerosols. It was of particular interest to what extent the fluxes above canopy deviate due to above mentioned processes from the particle dry deposition on the canopy foliage. The model simulations revealed that the particle concentration change due to aerosol dynamics can frequently exceed the effect of particle deposition even an order of magnitude or more. The impact is however strongly dependent on particle size and time. In spite of the fact that the time scale of turbulent transfer inside canopy is much smaller than the time scales of aerosol dynamics and dry deposition, letting to assume well mixed properties of air, the fluxes at the canopy top frequently deviate from deposition inside forest. This is due to transformation of aerosol concentration throughout the ABL and resulting complicated pattern of vertical transport. Therefore we argue that the comparison of time scales of aerosol dynamics and deposition defined for the processes below the flux measurement level do not unambiguously describe the importance of aerosol dynamics for vertical transport within canopy. We conclude that under dynamical conditions the micrometeorological particle flux measurements such as performed by the eddy covariance technique do not generally represent the dry deposition. The deviation can be systematic for certain size ranges so that the conclusion applies also to time averaged particle fluxes.

scholarly journals Aerosol dynamics within and above forest in relation to turbulent transport and dry deposition

2016 ◽  
Vol 16 (5) ◽  
pp. 3145-3160 ◽  
Author(s):  
Üllar Rannik ◽  
Luxi Zhou ◽  
Putian Zhou ◽  
Rosa Gierens ◽  
Ivan Mammarella ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Dry Deposition ◽  
Particle Deposition ◽  
Turbulent Transport ◽  
Flux Measurement ◽  
Vertical Transport ◽  
Forest Site ◽  
Aerosol Dynamics ◽  
Order Of Magnitude ◽  
The Impact

Abstract. A 1-D atmospheric boundary layer (ABL) model coupled with a detailed atmospheric chemistry and aerosol dynamical model, the model SOSAA, was used to predict the ABL and detailed aerosol population (characterized by the number size distribution) time evolution. The model was applied over a period of 10 days in May 2013 to a pine forest site in southern Finland. The period was characterized by frequent new particle formation events and simultaneous intensive aerosol transformation. The aim of the study was to analyze and quantify the role of aerosol and ABL dynamics in the vertical transport of aerosols. It was of particular interest to what extent the fluxes above the canopy deviate from the particle dry deposition on the canopy foliage due to the above-mentioned processes. The model simulations revealed that the particle concentration change due to aerosol dynamics frequently exceeded the effect of particle deposition by even an order of magnitude or more. The impact was, however, strongly dependent on particle size and time. In spite of the fact that the timescale of turbulent transfer inside the canopy is much smaller than the timescales of aerosol dynamics and dry deposition, leading us to assume well-mixed properties of air, the fluxes at the canopy top frequently deviated from deposition inside the forest. This was due to transformation of aerosol concentration throughout the ABL and resulting complicated pattern of vertical transport. Therefore we argue that the comparison of timescales of aerosol dynamics and deposition defined for the processes below the flux measurement level do not unambiguously describe the importance of aerosol dynamics for vertical transport above the canopy. We conclude that under dynamical conditions reported in the current study the micrometeorological particle flux measurements can significantly deviate from the dry deposition into the canopy. The deviation can be systematic for certain size ranges so that the time-averaged particle fluxes can be also biased with respect to deposition sink.

Effect of Particle Size Distribution on the Deep-Bed Capture Efficiency of an Exhaust Particulate Filter

2014 ◽  
Author(s):  
Sandeep Viswanathan ◽  
Stephen S. Sakai ◽  
Mitchell Hageman ◽  
David E. Foster ◽  
Todd Fansler ◽  
...  
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Particle Deposition ◽  
Operating Conditions ◽  
Particulate Filter ◽  
Particulate Emissions ◽  
Filter Loading ◽  
Particle Sizer ◽  
The Impact

The exhaust filtration analysis system (EFA) developed at the University of Wisconsin – Madison was used to perform micro-scale filtration experiments on cordierite filter samples using particulate matter (PM) generated by a spark-ignition direct injection (SIDI) engine fueled with gasoline. A scanning mobility particle sizer (SMPS) was used to characterize running conditions with four distinct particle size distributions (PSDs). The distributions selected differed in the relative number of accumulation versus nucleation mode particles. The SMPS and an engine exhaust particle sizer (EEPS) were used to simultaneously measure the PSD downstream of the EFA and the real-time particulate emissions from the SIDI engine to determine the evolution of filtration efficiency during filter loading. Cordierite filter samples with properties representative of diesel particulate filters (DPFs) were loaded with PM from the different engine operating conditions. The results were compared to understand the impact of particle size distribution on filtration performance as well as the role of accumulation mode particles on the diffusion capture of PM. The most penetrating particle size (MPPS) was observed to decrease as a result of particle deposition within the filter substrate. In the absence of a soot cake, the penetration of particles smaller than 70 nm was seen to gradually increase with time, potentially due to increased velocities in the filter as flow area reduces during filter loading, or due to decreasing wall area for capture of particles by diffusion. Particle re-entrainment was not observed for any of the operating conditions.

scholarly journals Green Preparation, Spheroidal, and Superior Property of Nano-1,3,5,7-Tetranittro-1,3,5,7-Tetrazocane

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Xinlei Jia ◽  
Jingyu Wang ◽  
Conghua Hou ◽  
Yingxin Tan
Keyword(s):  
Activation Energy ◽  
Particle Size ◽  
Fractal Dimension ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Fractal Theory ◽  
Crystal Form ◽  
Decomposition Temperature ◽  
Scanning Calorimetry ◽  
The Impact

Herein, a green process for preparing nano-HMX, mechanical demulsification shearing (MDS) technology, was developed. Nano-HMX was successfully fabricated via MDS technology without using any chemical reagents, and the fabrication mechanism was proposed. Based on the “fractal theory,” the optimal shearing time for mechanical emulsification was deduced by calculating the fractal dimension of the particle size distribution. The as-prepared nano-HMX was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). And the impact sensitivities of HMX particles were contrastively investigated. The raw HMX had a lower fractal dimension of 1.9273. The ideal shearing time was 7 h. The resultant nano-HMX possessed a particle size distribution ranging from 203.3 nm to 509.1 nm as compared to raw HMX. Nano-HMX particles were dense spherical, maintaining β-HMX crystal form. In addition, they had much lower impact sensitivity. However, the apparent activation energy as well as thermal decomposition temperature of nano-HMX particles was decreased, attributing to the reduced probability for hotspot generation. Especially when the shearing time was 7 h, the activation energy was markedly decreased.

scholarly journals Effects of aerosol dynamics and gas–particle conversion on dry deposition of inorganic reactive nitrogen in a temperate forest

2020 ◽  
Vol 20 (8) ◽  
pp. 4933-4949 ◽  
Author(s):  
Genki Katata ◽  
Kazuhide Matsuda ◽  
Atsuyuki Sorimachi ◽  
Mizuo Kajino ◽  
Kentaro Takagi
Keyword(s):  
Dry Deposition ◽  
Particle Deposition ◽  
Chemical Transport ◽  
Reactive Nitrogen ◽  
Surface Model ◽  
Deposition Flux ◽  
Transport Models ◽  
Inorganic Particles ◽  
Aerosol Dynamics ◽  
Chemical Transport Models

Abstract. Dry deposition has an impact on nitrogen status in forest environments. However, the mechanism for the high dry-deposition rates of fine nitrate particles (NO3-) observed in forests remains unknown and is thus a potential source of error in chemical transport models (CTMs). Here, we modified and applied a multilayer land surface model coupled with dry-deposition and aerosol dynamic processes for a temperate mixed forest in Japan. This represents the first application of such a model to ammonium nitrate (NH4NO3) gas–particle conversion (gpc) and the aerosol water uptake of reactive nitrogen compounds. Thermodynamics, kinetics, and dry deposition for mixed inorganic particles are modeled by a triple-moment modal method. Data for inorganic mass and size-resolved total number concentrations measured by a filter pack and electrical low-pressure impactor in autumn were used for model inputs and subsequent numerical analysis. The model successfully reproduces turbulent fluxes observed above the canopy and vertical micrometeorological profiles noted in our previous studies. The sensitivity tests with and without gpc demonstrated clear changes in the inorganic mass and size-resolved total number concentrations within the canopy. The results also revealed that within-canopy evaporation of NH4NO3 under dry conditions significantly enhances the deposition flux of fine-NO3- and fine-NH4+ particles, while reducing the deposition flux of nitric acid gas (HNO3). As a result of the evaporation of particulate NH4NO3, the calculated daytime mass flux of fine NO3- over the canopy was 15 times higher in the scenario of “gpc” than in the scenario of “no gpc”. This increase caused high contributions from particle deposition flux (NO3- and NH4+) to total nitrogen flux over the forest ecosystem (∼39 %), although the contribution of NH3 was still considerable. A dry-deposition scheme coupled with aerosol dynamics may be required to improve the predictive accuracy of chemical transport models for the surface concentration of inorganic reactive nitrogen.

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