Electrification of particulate entrained fluid flows—Mechanisms, applications, and numerical methodology

Cheng

et al. 2017

Aerosol Air Qual. Res.

Self Cite

Hourly particulate matter mass concentrations and meteorological parameters, recorded by the China National Environmental Monitoring Center (CNEMC) and China Observatory, between June 2013 and March 2016 in Beijing, Xi'an, Shanghai and Guangzhou were examined to explore correlations. Characteristics of a rapid (abrupt) rise in PM 2.5 mass concentration during early stage of a serious urban PM pollution event were examined and compared with pollution events with a gradual (accumulative) rise in PM 2.5 mass concentration. The accumulative rise in air pollution is characterized by a prolonged slow PM 2.5 growth rate (3-5 µg m -3 h -1 ), and could eventually lead to middle level pollution (ambient PM 2.5 mass concentration of about 150 µg m -3 ), accompanied with an uncertain temporal variation in SO 2 , NO 2 , O 3 and CO concentrations. The abrupt rise process is characterized by a short-term high aerosol growth rate (> 10 µg m -3 h -1), and could eventually form severe air pollution (PM 2.5 mass concentration exceeds 250 µg m -3 ), with a constant increase in gaseous pollutants concentrations. The average relative humidity (RH) was observed to have a less impact on the rise of PM 2.5 concentration, but the fluctuation in RH was found to have a strong correlation with the rise in PM 2.5 concentration. Further analysis has indicated that both abrupt and accumulative rise in PM 2.5 mass concentration could be due to the RH fluctuation in atmosphere. The RH variation is important for the study of the fine-particle growth and for prediction of PM pollution episodes.

Section: Introductionmentioning

confidence: 99%

Impact of Air Humidity Fluctuation on the Rise of PM Mass Concentration Based on the High-Resolution Monitoring Data

Cheng

et al. 2017

Aerosol Air Qual. Res.

Self Cite

“…ΔTa is inversely proportional to the third power of the particle radius. Therefore, for two different sized ice particles with the same initial temperature, the small particle with higher temperature acquires negative charge and the large particle with lower temperature acquires positive charge after collision and separation [36], as shown in Fig. 3.…”

Section: Thermoelectric Effectmentioning

confidence: 96%

Towards the Understanding of Ice Crystal-graupel Collision Charging in Thunderstorm Electrification

He¹,

D²,

Lü³

et al. 2018

Preprint

Self Cite

Thunderstorm electrification has been studied for hundreds of years. Several mechanisms have been proposed to elucidate the electrification, including convective charging, inductive precipitation charging, and ice crystal-graupel collision charging. Field observations and model studies have demonstrated the vital roles that graupel and ice crystals play in the electrification, but the mechanism of the collision charging is still unclear. The fundamental essence of relative growth rate theory used for explaining the tripole charge structure in thunderclouds also needs a further exploration. We analyze the processes of ice crystal-graupel collision charging from charge migration inside hydrometeors to charge separation between two hydrometeors. The driving effects of temperature gradient and chemical potential gradient in charge migration are clarified, as well as the applicability of the relative growth rate theory, thermoelectric effect and surface tension gradient in different humidities. Based on the understanding from these electrification mechanisms, we propose that the essence of charge separation is driven by non-thermal equilibrium, and future studies on thunderstorm electrification should focus on the dynamical non-thermal equilibrium of cloud particles.

“…1a), over the period from 21 March to 2 June 2017. The area was selected since it lies within a dusty belt in the Hexi Corridor (Wang et al, 2018), which is mainly affected by the Mongolian cyclones (and probably by the cold downdrafts from thunderstorms/squall) during the observational period and is therefore frequently subjected to dust events (Shao, 2000;Williams et al, 2009). At the Qingtu Lake Observational Array (QLOA) site, there is a prevailing wind direction, along with a straight line having a mean angle of ∼ 247.5 • with respect to the north (approximately 74.6 % frequency), as shown in Fig.…”

Section: Description Of the Field Sitementioning

confidence: 99%

“…The F test is used for testing the SLR model. Previous studies have shown that charge transfer processes are nonlinearly related to the ambient temperature and RH (Gu et al, 2013;Lacks and Sankaran, 2011;McCarty and Whitesides, 2008;Wei and Gu, 2015;Zheng et al, 2014). We thus use the following MLR to evaluate the effects of ambient temperature and RH on µ * :…”

Section: Regression Analysismentioning

confidence: 99%

“…Measurements of electrical effects in dust events (especially dust storms) have been made for over 100 years, dating back to 1913 with the finding that the atmospheric vertical E-fields increased by 1-3 orders of magnitude and reversed their direction during dust storms (Rudge, 1913;Schmidt et al, 1998;Williams et al, 2009). However, owing to the difficulty in monitoring random dust events, only several tens of events are recorded in the literature (see Table 3 in Zheng, 2013, for details).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Quantifying the large-scale electrification equilibrium effects in dust storms using field observations at Qingtu Lake Observatory

Zheng

2018

Atmos. Chem. Phys.

Abstract. Dust and sand electrification, which is a ubiquitous phenomenon in dust events, has a potentially dramatic effect on dust and sand lifting and transport processes. However, the effect of such electrification is still largely unclear, mainly due to its complexity and sparse observations. Here, we conducted an extensive observational analysis involving mild and severe dust storms with minimum visibility, ranging from ∼0.09 to 0.93 km, to assess the electrical properties of airborne dust particles in dust storms. The space charge density has been estimated indirectly based on Gauss's law. Using the wavelet coherence analysis that is a method for evaluating the correlations between two non-stationary time series in the time–frequency domain, we found that the space charge density and dust concentration were significantly correlated over the 10 min timescales (on the order of the typical integral timescale of atmospheric turbulence). We further presented a simple linear regression (SLR) model to quantify such large timescale correlations and found that there was a significant linear relationship between space charge density and dust concentration at given ambient temperature and relative humidity (RH), suggesting that the estimated mean charge-to-mass ratio of dust particles was expected to remain constant (termed as the equilibrium value μ∗). In addition, the influences of ambient temperature and RH on μ∗ were evaluated by a multiple linear regression (MLR) model, showing that the μ∗ is nonlinearly related to environmental factors. The present study provides observational evidence for the environmental-dependent electrification equilibrium effects in dust storms. This finding may reduce challenges in future quantifications of dust electrification, as it is possible to exclude effects, such as the particles' collisional dynamics, on dust electrification.