Aerosol Concentration Distribution Research Articles

Assessment of Occupational Exposure to Inhalable Aerosols in an Instant Powdered Food Manufacturing Plant in Norway

BackgroundIn the food manufacturing industry, exposure to inhalable aerosols contributes to respiratory illnesses such as occupational asthma and rhinitis. However, there is a lack of comprehensive exposure assessment studies. This study evaluated occupational exposure to inhalable aerosols in an instant powdered food manufacturing plant during work operations involving dried food and powders. MethodsIn total, 50 workers from an instant powdered food manufacturing plant were recruited. Personal inhalable aerosol exposure measurements were taken for both full-shift and task-based activities. The concentrations of inhalable aerosols were analyzed to identify any variation within and across departments, as well as between seasons, handedness, and sex. ResultsIn total, 134 personal air samples were collected, and the particulate mass was determined gravimetrically. The concentrations of inhalable aerosols ranged from 0.1 to 27 mg/m3 for full-shift exposure measurements and 3.1 to 73 mg/m3 for task-based measurements. Statistically significant differences in mean aerosol concentrations were found across departments (A:B p < 0.001, A:C p < 0.05, B:C p < 0.001) and between seasons (p < 0.001). ConclusionThis study revealed high exposure to inhalable aerosols among workers, particularly those involved in manual weighing, mixing, and adding powders. The significant differences between departments highlight the specific activities contributing to increased inhalable aerosol concentrations. Seasonal variations were also evident, with autumn showing higher concentrations of inhalable aerosols in all departments compared with summer. These findings emphasize the importance of understanding the distribution of aerosol concentrations across different work tasks and departments, particularly during different seasons.

Study on aerosol thermophoretic force and thermophoresis deposition model in reactor building

During nuclear reactor severe accident, the input of external passive containment cooling system will result in significant aerosol thermophoresis deposition in reactor building, which plays important factor affecting the safety assessment of nuclear reactor. Ratio of aerosol particles radius and gas molecule mean free path (Kn number) in reactor building is not greater than 2, corresponding to the near-continuous medium zone and transition zone. Firstly the typical thermophoretic force equations for these zones are evaluated. Combined with key influencing factors analysis, the correction factor connected to Kn number is introduced to address the deviation in the prediction for the transition zone of the current equations. The modified thermophoretic force equation obviously improves the underestimation of the original equation and is then used to obtain the thermophoresis deposition coefficient. According to experimental validation, the obtained coefficient is more accurate than the model that is widely employed in analysis codes in predicting the thermophoresis deposition of aerosol particles. Finally, fluid continuity, momentum, energy and particle continuity equations are established with deduced thermophoresis deposition coefficient and solved numerically. The thermophoresis deposition model considering natural convection (CT model) is established by theoretical derivation and fitting with the numerical solutions. By introducing the effects of natural convection on temperature distribution and aerosol concentration distribution the CT model could accurately describe the aerosol thermophoresis deposition behavior under natural convection conditions for Kn number is not greater than 2, which can be applied to aerosol thermophoresis deposition prediction in reactor building.

Calculation of Concentration Distribution of Steady Flow Aerosol by Langevin Dynamics Method

Langevin dynamics (LD) method is a modelling technique using pseudo-random numbers to reproduce the acceleration of aerosol particles due to random collisions of gas molecules onto the particles. Although the LD method can reproduce the Brownian motion of particles and motion due to inertial force and/or external force, it is difficult to understand the behavior of aerosol, which is group of particles, from the information on the motion of individual particles. In this study, a novel calculation method was developed to obtain the concentration distribution of aerosol by accumulating the information of position of particles calculated by the LD method, and it was applied to the diffusion of aerosol flowing steadily in a cylindrical tube. The concentration distribution obtained by this method agreed well with that obtained by solving the conventional convective-diffusion equation. Furthermore, change in cup-mixing concentration of aerosol in axial direction calculated from the concentration distribution agreed well also with the penetration expressed by Gormley & Kennedy.

Spatiotemporal and Vertical Distribution of Asian Tropopause Aerosol Layer Using Long-Term Multi-Source Data

The Asian tropopause aerosol layer (ATAL) is an enhanced aerosol concentration layer in the upper troposphere and lower stratosphere over Asia, and it has important effects on radiation balance, atmospheric circulation, regional climate, and atmospheric chemical processes. However, despite its importance, the specific structure and long-term variation trend of the ATAL have been rarely analyzed, which is critical for assessing the impact of ATAL on climate change and evaluating the performance of climate models. This study compared and analyzed the three-dimensional spatial distribution characteristics and temporal variability using CALIPSO, SAGEII, and MERRA-2 data and discussed the possible causes of the variation. The results showed that the ATAL began to appear in the mid-to-late 1990s and then strengthened rapidly until 2010, after which this trend was no longer observed. Moreover, significant heterogeneity existed in the distribution of aerosol concentration in the ATAL, showing north–south differences (NSDs) in both time and space. In addition, it was found that besides surface emissions, atmospheric circulation, the strength of convective transport, and stratosphere–troposphere exchange processes also contribute to this pattern. This study has important implications for quantifying the climate consequences of the ATAL.

Sparse Inversion of Aerosol Concentration Distribution Based on LIDAR Remote Sensing

Sparse Inversion of Aerosol Concentration Distribution Based on LIDAR Remote Sensing

Patterns of SARS-CoV-2 aerosol spread in typical classrooms

Although current industry guidelines to control the spread of aerosols such as SARS-CoV-2 (COVID-19) have adopted a six-foot (~1.8 m) spacing between individuals indoors, recent evidence suggests that longer range spread is also responsible for infections in public spaces. The vehicle for long-range spread is smaller (<5 μm) droplets or particles, termed bio-aerosols, or aerosols for short, which have a large surface area to volume ratio such that aerodynamic drag is much larger than gravity forces. The aerosols remain suspended in air for extended time periods, and they essentially move with air currents. Prediction of the danger to occupants in a closed room when exposed to an infected individual requires knowledge of the period of exposure and the concentration level of aerosols in the breathing zone of an occupant. To obtain an estimate of the concentration level, a common assumption is well-mixed conditions within an interior space. This is obtained from a mass balance between the level of aerosol produced by an infected individual along with the airflow rate into and out of the entire space. In this work, we use computational fluid dynamics, compared with experimental results in several cases, to explore the aerosol concentration distribution in a typical classroom for several common conditions and compare these results to the well-mixed assumption. We use a tracer gas to approximately simulate the flow and dispersion of the aerosol-air mixture. The two ventilation systems examined, ceiling diffusers and open windows, yield average concentrations at occupant breathing level 50 % greater than the well mixed case, and some scenarios yield concentrations that are 150 % greater than the well mixed concentration at specific breathing-level locations. Of particular concern are two conditions: horizontal air flow from an open window in line with a row of seating and, second, an infected individual seated near a sealed cold window. For the former, conditions are improved if a baffle is placed inside the open window to direct the air toward the floor, creating a condition similar to displacement ventilation. In the latter, the cold air flowing down along the cold window recirculates aerosols back into the breathing zone. Adding window covers or a portable heater below the window surface will moderate this condition.

Study on the distribution characteristics of aerosol produced by powder dumping in glove box

Objective To investigate the effects of particle size, wind speed and dumping velocity on aerosol concentration distribution during powder dumping in a reprocessing plant. Methods CeO 2 powder was selected as the substitute material of PuO 2. FLUENT software was used to calculate the pouring process of CeO 2 powder under different operation conditions. Then the aerosol concentration distribution under different dumping speeds was measured by particle size spectrometer to verify the accuracy of simulation results. Results The particles with small particle size are more likely to be separated from the mainstream area by the drag force of the surrounding gas, and the radius of the diffusion range also increases with the decrease of the particle size. 2) When the ventilation speed is less than 1 m/s, the dust lifting can be reduced and the concentration of dust particles in the chamber can be reduced to a certain extent. 3) In the process of powder dumping, the spoon is rotated anticlockwise at a speed of 100° in 2~3 s, and less dust aerosol is produced on the right side of the tray. Conclusion When operating the powder particles with smaller particle size, more attention should be paid to the monitoring of aerosol at different positions; the change of air inlet velocity makes the flow field in glove box more complex, and the volume fraction of dust particles is related to the size and location of vortex formed by airflow. The greater the wind speed, the greater the impact on the powder dumping process. The experimental results are basically consistent with the simulation results, and the results show that the lower the dumping speed, the smaller the aerosol concentration near the tray. 摘要： 目的 考察粒径、风速和倾倒速度对后处理厂粉末倾倒过程产生的气溶胶浓度分布的影响。 方法 选择 CeO 2 粉末作为 PuO 2 替代材料, 用 FLUENT 软件对不同操作条件下 CeO 2 粉末倾倒过程进行数值计算, 再利用粒径谱 仪对不同倾倒速度下的气溶胶浓度分布进行测量, 验证模拟结果准确性。 结果 小粒径的颗粒更可能受周围气体的 曳力影响而从主流区域脱离出来形成散射粉尘, 其扩散范围的半径也随着粒径的减小而扩大。通风速度在 1 m/s 以下可以减少操作过程粉尘的扬起, 在一定程度上降低箱室内粉尘颗粒的浓度。粉末倾倒过程, 以 2~3 s 将勺子逆时 针旋转 100° 的速度倾倒粉末在托盘右侧产生的粉尘气溶胶较少。 结论 在对粒径较小的粉末颗粒进行操作时, 不同 位置气溶胶的监测应该引起更多的关注;进风速度的变化使得手套箱内的流场变得复杂, 粉尘颗粒的体积分数与气流 形成涡流的大小和涡流位置有关, 风速越大, 对粉末倾倒过程的影响越大;实验结果与模拟结果基本相符, 较慢的倾倒 速度在托盘附近处产生的气溶胶颗粒较少。

Dual-channel mobile fluorescence lidar system for detection of tryptophan.

We present a dual-channel mobile lidar system based on laser-induced fluorescence (LIF) for real-time standoff detection and concentration distribution analysis of tryptophan. The system employs an ultraviolet laser excitation source and signal detectors for receiving fluorescence signals within two different wavelength bands. The performed experiments measured tryptophan aerosols at two different standoff distances. Moreover, distilled water and ethanol solutions were also detected for comparison. The results show that the system can detect LIF signals of tryptophan, give early warnings, locate the diffusion sources, and monitor the variation of the aerosol concentration distribution in real time.

Simulated coordinated impacts of the previous autumn North Atlantic Oscillation (NAO) and winter El Niño on winter aerosol concentrations over eastern China

Abstract. The high aerosol concentration (AC) over eastern China has attracted attention from both science and society. Based on the simulations of a chemical transport model using a fixed emissions level, the possible impact of the previous autumn North Atlantic Oscillation (NAO) combined with the simultaneous El Niño–Southern Oscillation (ENSO) on the boreal winter AC over eastern China is investigated. We find that the NAO only manifests its negative impacts on the AC during its negative phase over central China, and a significant positive influence on the distribution of AC is observed over south China only during the warm events of ENSO. The impact of the previous NAO on the AC occurs via an anomalous sea surface temperature tripole pattern by which a teleconnection wave train is induced that results in anomalous convergence over central China. In contrast, the occurrence of ENSO events may induce an anomalous shift in the western Pacific subtropical high and result in anomalous southwesterlies over south China. The anomalous circulations associated with a negative NAO and El Niño are not favorable for the transport of AC and correspond to worsening air conditions over central and south China. The results highlight the fact that the combined effects of tropical and extratropical systems play a considerable role in affecting the boreal winter AC over eastern China.

Atmosphere Boundary Layer Height (ABLH) Determination under Multiple-Layer Conditions Using Micro-Pulse Lidar

Accurate estimation of the atmospheric boundary layer height (ABLH) is critically important and it mainly relies on the detection of the vertical profiles of atmosphere variables (temperature, humidity,’ and horizontal wind speed) or aerosols. Aerosol Lidar is a powerful remote sensing instrument frequently used to retrieve ABLH through the detection of the vertical distribution of aerosol concentration. A challenge is that cloud, residual layer (RL), and local signal structure seriously interfere with the lidar measurement of ABLH. A new objective technique presenting as giving a top limiter altitude is introduced to reduce the interference of RL and cloud layer on ABLH determination. Cloud layers are identified by looking for the rapid increase and sharp attenuation of the signal combined with the relative increase in the signal. The cloud layers whether they overlay the ABL are classified or are decoupled from the ABL are classified by analyzing the continuity of the signal below the cloud base. For cloud layer capping of the ABL, the limiter is determined to be the altitude where a positive signal gradient first occurs above the cloud upper edge. For a cloud that is decoupled from the ABL, the cloud base is considered to be the altitude limiter. For RL in the morning, the altitude limiter is the greatest positive gradient altitude below the RL top. The ABLH will be determined below the top limiter altitude using Haar wavelet (HM) and the curve fitting method (CFM). Besides, the interference of local signal noise is eliminated through consideration of the temporal continuity. While comparing the lidar-determined ABLH by HM (or CFM) and nearby radiosonde measurements of the ABLH, a reasonable concordance is found with a correlation coefficient of 0.94 (or 0.96) and 0.79 (or 0.74), presenting a mean of the relative absolute differences with respect to radiosonde measurements of 10.5% (or 12.3%) and 22.3% (or 17.2%) for cloud-free and cloudy situations, respectively. The diurnal variations in the ABLH determined from HM and CFM on four selected cases show good agreement with a mean correlation coefficient higher than 0.99 and a mean absolute bias of 0.22 km. Also, the determined diurnal ABLH are consistent with surface turbulent kinetic energy (TKE) combined with the time-height distribution of the equivalent potential temperature.

Determination of boundary layer top on the basis of the characteristics of atmospheric particles

The planetary boundary layer (PBL) is the lowest layer of the atmosphere that can be directly influenced with the Earth's surface. This layer can also respond to surface forcing. The determination of the PBL is significant to environmental and climate research. PBL can also serve as an input parameter for further data processing with atmospheric models. Traditional detection algorithms are susceptible to errors associated with the vertical distribution of aerosol concentrations. To overcome this limitation, a maximum difference search (MDS) algorithm was proposed to calculate the top of the boundary layer based on differences in particle characteristics. The top positions of the PBL from MDS algorithm under different convection states were compared with those from conventional methods. Experimental results demonstrated that the MDS method can determine the top of the boundary layer precisely. The proposed algorithm can also be used to calculate the top of the PBL accurately under weak convection conditions where the traditional methods cannot be applied. Finally, experimental data from June 2015 to December 2015 were analysed to verify the reliability of the MDS algorithm. The correlation coefficients R2 (RMSE) between the results of MDS algorithm and radiosonde measurements were 0.53 (115 m), 0.79 (141 m) and 0.96 (43 m) under weak, moderate and strong convections, respectively. These findings indicated that the proposed method possessed a good feasibility and stability.

Monitoring the industrial sources of aerosol in Cubatao, Brazil, using a scanning elastic lidar and a lidar doppler

Field campaigns with a scanning multiwavelength elastic lidar coupled with a Doppler system to monitor industrial atmospheric aerosol emissions were carried out, with the objective of monitoring aerosol emission sources and plume dispersion. Since the technique provides information on the spatial and temporal distribution of aerosol concentration, the implementation of a systematic monitoring procedure is proposed as a valuable tool in air quality monitoring applied to regions of interest.

Simulated contrasting influences of two La Niña Modoki events on aerosol concentrations over eastern China

AbstractUsing the Goddard Earth Observing System (GEOS)‐Chem model driven by GEOS‐4 assimilated meteorological data, the potential influence of two La Niña Modoki events on aerosol concentrations over eastern China is explored. The results indicate that the impact of La Niña Modoki on aerosol concentrations differs between strong and moderate events. During the mature phase of the strong event of 1998/1999, an anomalous dipole pattern is observed over eastern China, i.e., with increased aerosol concentrations in the south and reduced concentrations in the north. The dipole pattern in the moderate event of 2000/2001 is reversed, with reduced aerosol concentrations in the south and increased concentrations in north China. Additionally, decreased aerosol concentrations are seen in spring of the decaying phase for the 1998/1999 event, while in the decaying spring of the 2000/2001 event, the dipole is reversed relative to the mature phase. During the decaying summer, aerosol concentrations are found to increase over eastern China in the 1998/1999 event but not in the 2000/2001 event. These anomalous aerosol concentrations are mainly caused by changes in circulation associated with the two La Niña Modoki events. In contrast, the role of wet deposition is observed to be limited during the lifespan of these two events. It is also found that the potential influence of the two La Niña Modoki events on aerosol concentrations can be up to 20% of the climatological mean. This suggests that La Niña Modoki has an important role in determining the distribution of aerosol concentrations over eastern China.

Modelling multi-component aerosol transport problems by the efficient splitting characteristic method

In this paper, a splitting characteristic method is developed for solving general multi-component aerosol transports in atmosphere, which can efficiently compute the aerosol transports by using large time step sizes. The proposed characteristic finite difference method (C-FDM) can solve the multi-component aerosol distributions in high dimensional domains over large ranges of concentrations and for different aerosol types. The C-FDM is first tested to compute the moving of a Gaussian concentration hump. Comparing with the Runge-Kutta method (RKM), our C-FDM can use very large time step sizes. Using Δt = 0.1, the accuracy of our C-FDM is 10−4, but the RKM only gets the accuracy of 10−2 using a small Δt = 0.01 and the accuracy of 10−3 even using a much smaller Δt = 0.002. A simulation of sulfate transport in a varying wind field is then carried out by the splitting C-FDM, where the sulfate pollution is numerically showed expanding along the wind direction and the effects of the different time step sizes and different wind speeds are analyzed. Further, a realistic multi-component aerosol transport over an area in northeastern United States is studied. Concentrations of PM2.5 sulfate, ammonium, nitrate are high in the urban area, and low in the marine area, while sea salts of sodium and chloride mainly exist in the marine area. The normalized mean bias and the normalized mean error of the predicted PM2.5 concentrations are −6.5% and 24.1% compared to the observed data measured at monitor stations. The time series of numerical aerosol concentration distribution show that the strong winds can move the aerosol concentration peaks horizontally for a long distance, such as from the urban area to the rural area and from the marine area to the urban and rural area. Moreover, we also show the numerical time duration patterns of the aerosol concentration distributions due to the affections of the turbulence and the deposition removal. The developed splitting C-FDM algorithm can be applied to model spatial multi-component aerosol transport problems in large domains in atmosphere.

Analysis of Operation of Electrostatic Precipitators at High Concentrations of Fine Dispersed Phase

Analysis of operation of electrostatic precipitators at high concentrations of the fine dispersed phase is given here. Changes in the parameters of the electrostatic precipitator in the presence of the dispersed phase are considered. Theoretical analysis of the process of corona discharge locking is given. Calculation results of electric field voltage distribution in the presence of a charged dispersed phase and the distribution of aerosol concentration over the cross section of the electrode gap are given. The expediency of using discharge electrodes with a low corona discharge ignition voltage is demonstrated.

A Global Atmospheric Contaminant Transport Model Based on 3D Advection-Diffusion Equation

To study the global air pollution concentration and evaluate the impact of regional pollution on whole earth, a global atmospheric contaminant transport model is established based on 3D advection-diffusion equation, which captures the processes of advection by wind and turbulent diffusion during atmospheric dispersion. The Eulerian finite difference method is employed for numerical solution of the proposed model. Then one-year aerosol transport on global scale is simulated using the proposed model, and the simulation results are verified against the real remote sensing data of NASA. It turns out that the simulated values of aerosol concentration are strongly correlated with the real values and the correlation coefficient is above 0.8 for sample point. Furthermore, the proposed model is used for predicting the next-year global atmospheric contaminant concentration by simulation. Compared with the related models on atmospheric contaminant transport, we propose a model in this paper with three appealing features: three-dimensional (3D), global scale, and targeted for aerosol transport simulation. In this paper, we present the global 3D atmospheric contaminant transport model and simulate the transport of aerosol around the world. This proposed model uses 3D space coordinates which can fully address the spread of pollutants in space. In this mode, the wind speed and turbulent diffusivity are considered. Furthermore, a comprehensive term is introduced into the model to take into account the factors of emission source, chemical conversion, dry deposition and wet scavenging. The parameters in the model are variables changing over time and space. For simulation purposes, the horizontal resolution of the model is 45 oo × , and the vertical direction is divided into 11 layers. We first simulate the aerosol diffusion in the world in one year. It turns out that the simulated global aerosol concentration distribution is consistent with the real aerosol concentration distribution. Actually, the simulated value has strong correlation with the real data, and the correlation coefficient is above 0.8 for sample point. We also predict the global aerosol concentration over next year. Hence, the proposed model in this paper can be a useful tool for predicting the global aerosol concentration. If we combine this model with more precise chemical patterns, the accuracy of the model can be improved and the proposed model can be further extended to study other atmospheric contaminants. The rest of paper is organized as follows. Section II introduces the proposed global atmospheric contaminant transport model based on 3D advection-diffusion equation. Numerical solution of the proposed model is given in Section III. Section IV presents and discusses the simulation results. Finally, conclusions are drawn in Section V.

축산관련차량 이동에 따른 도로의 에어로졸 발생량 분석

Most of livestock houses are concentrated in certain area with mass rearing system resulting in rapid spread of infectious diseases such as HPAI (highly pathogenic avian influenza). The livestock-related vehicles which frequently travel between farms could be a major factor for disease spread by means of transmission of airborne aerosol including pathogens. This study was focused on the quantitative measurement of aerosol concentration by field experiment while vehicles were passing through the road. The TSP (total suspended particle) and PM10 (particle matter) were measured using air sampler with teflon filter installed downward the road with consideration of weather forecast and the direction of road. And aerosol spectrometer and video recorders were also used to measure the real-time distribution of aerosol concentration by its size. The results showed that PM2.5 was not considerable for transmission of airborne aerosol from the livestock-related vehicle. The mass generated from the road during the vehicle movement was measured and calculated to 241.4 <TEX>${\mu}g/m^3$</TEX> by means of the difference between TSP and PM2.5. The dispersion distance was predicted by 79.6 m from the trend curve.

Modelling aerosol concentration distributions from transient (puff) sources

A field trial involving 50 separate releases of inert aerosol (kaolin) was conducted to determine the concentration distribution within aerosol puffs resulting from near-instantaneous releases. Atmospheric conditions during the trial fell within Pasquill stability classes A and B (very and moderately unstable, respectively). Aerosol concentration measurements were made using a scanning lidar system operating at 1·06 μm. Artificial neural network (ANN) models were developed using the data to predict concentration distributions, given a number of meteorological parameters. The ANN predictions were compared to those from traditional Gaussian puff models, and provided better predictions than the Gaussian model parameterizations examined. The ANN models were also used to develop Gaussian fitting parameters to replace traditional Pasquill and Slade dispersion coefficients. The ANN-derived dispersion coefficients provided better predictions of measured puff concentration distributions than either the Pasquill or Slade parameterizations, though the full multi-input ANN models provided even better predictions than the Gaussian puff model using ANN-derived dispersion coefficients.

Size distributions of aerosol and water-soluble ions in Nanjing during a crop residual burning event

To investigate the impact on urban air pollution by crop residual burning outside Nanjing, aerosol concentration, pollution gas concentration, mass concentration, and water-soluble ion size distribution were observed during one event of November 4−9, 2010. Results show that the size distribution of aerosol concentration is bimodal on pollution days and normal days, with peak values at 60−70 and 200−300 nm, respectively. Aerosol concentration is 104 cm−3•nm−1 on pollution days. The peak value of spectrum distribution of aerosol concentration on pollution days is 1.5−3.3 times higher than that on a normal day. Crop residual burning has a great impact on the concentration of fine particles. Diurnal variation of aerosol concentration is trimodal on pollution days and normal days, with peak values at 03:00, 09:00 and 19:00 local standard time. The first peak is impacted by meteorological elements, while the second and third peaks are due to human activities, such as rush hour traffic. Crop residual burning has the greatest impact on SO2 concentration, followed by NO2, O3 is hardly affected. The impact of crop residual burning on fine particles (< 2.1 μm) is larger than on coarse particles (> 2.1 μm), thus ion concentration in fine particles is higher than that in coarse particles. Crop residual burning leads to similar increase in all ion components, thus it has a small impact on the water-soluble ions order. Crop residual burning has a strong impact on the size distribution of K+, Cl−, Na+, and F− and has a weak impact on the size distributions of NH4+, Ca2+, NO3− and SO42−.

Hyper-cooling in the nocturnal boundary layer: the Ramdas paradox

Characterizing the interaction between turbulence and radiative processes is necessary for understanding the nocturnal atmospheric boundary layer. The subtle nature of the interaction is exemplified in a phenomenon called the ‘Ramdas paradox’ or the ‘lifted temperature minimum’ (LTM), involving preferential cooling near the Earth's surface. The prevailing explanation for the LTM (the VSN model, Vasudeva Murthy et al (1993 Phil. Trans. R. Soc. A 344 183–206)) invokes radiative exchange in a homogeneous nocturnal atmosphere to predict a large cooling of the near-surface air layers. It is shown here that the cooling predicted by the VSN model is spurious, and that any preferential cooling can occur only in a heterogeneous atmosphere. The underlying error is fundamental, and occurs to varying degrees in a wide class of radiative models, in a flux-emissivity formulation, the VSN model being a prominent example. We, for the first time, propose the correct flux-emissivity formulation that eliminates spurious cooling. Results from field observations and laboratory experiments presented here, however, show that the near-surface radiative cooling is real; near-surface cooling rates can be orders of magnitude higher than values elsewhere in the boundary layer. The results presented include the dependence of the LTM on turbulence, the surface emissivity and the thermal inertia of the ground. It is proposed that aerosols provide the heterogeneity needed for the preferential cooling mechanism. Turbulence, by determining the aerosol concentration distribution over the relevant length scales, plays a key role in the phenomenon. Experimental evidence is presented to support this hypothesis.