Investigating the effect of volatility on the hygroscopicities of acetate nanoparticle aerosols by surface plasmon resonance microscopy.

Under high relative humidity (RH) conditions, the release of volatile components (such as acetate) has a significant impact on the aerosol hygroscopicity. In this work, one surface plasmon resonance microscopy (SPRM) measurement system was introduced to determine the hygroscopic growth factors (GFs) of three acetate aerosols separately or mixed with glucose at different RHs. For Ca(CH3COO)2 or Mg(CH3COO)2 aerosols, the hygroscopic growth trend of each time was lower than that of the previous time in three cyclic humidification from 70% RH to 90% RH, which may be due to the volatility of acetic acid leading to the formation of insoluble hydroxide (Ca(OH)2 or Mg(OH)2) under high RH conditions. Then the third calculated GF (using the Zdanovskii-Stokes-Robinson method) for Ca(CH3COO)2 or Mg(CH3COO)2 in bicomponent aerosols with 1:1 mass ratio were 3.20% or 5.33% lower than that of the first calculated GF at 90% RH. The calculated results also showed that the hygroscopicity change of bicomponent aerosol was negatively correlated with glucose content, especially when the mass ratio of Mg(CH3COO)2 to glucose was 1:2, the GF at 90% RH only decreased by 4.67% after three cyclic humidification. Inductively coupled plasma atomic emission spectrum (ICP-AES) based measurements also indicated that the changes of Mg2+concentration in bicomponent was lower than that of the single-component. The results of this study reveal thatduring the efflorescence transitions of atmospheric nanoparticles, the organic acids diffusion rate may be inhibited by the coating effect of neutral organic components, and the particles aging cycle will be prolonged.

Characterization of the vertical evolution of urban nocturnal boundary layer by UAV measurements: Insights into relations to cloud radiative effect.

The complex structure of the nocturnal boundary layer (NBL) and its impact on air pollution remain poorly understood. In this study, we present in-situ nocturnal flight measurements onboard an unmanned aerial vehicle (UAV) during the wintertime of 2022 at an urban site in Hefei, China. Besides, co-located measurements of radiation intensity and total amount of cloud were conducted. The vertical distribution of temperature, particle number concentration, and relative humidity were obtained to study the structure of NBL and the key factors driving the evolution of the NBL. A multi-layer inversion boundary layer was observed during haze and fog episodes, which affects the vertical diffusion of particles near the surface and leads to a vertical gradient of particle number concentrations. The particle size distribution demonstrates a drastic vertical variation over different sections of the nocturnal boundary layer: homogeneously mixed in the SBL and the RL layer, sharply reduced in the IL. It is found that the temperature and particle number concentration differences between near-surface and at 500 m are highly related to variations of the radiation intensity and the amount of cloud. The decreased cloud cover enhances the surface cooling, creating a shallow NBL with multiple inversion layers, which reinforces the suppression of vertical diffusions and consequently promotes the accumulation of aerosols within the NBL. This reveals an important mechanism for the impact of NBL evolution modulated by cloud radiative effect on the formation of urban haze.

Retrieval of refractive index of ultrafine single particle using hygroscopic growth factor obtained by high sensitive surface plasmon resonance microscopy.

When exposed to different relative humidities (RHs), the optical properties of atmospheric aerosols will change because of changes in the aerosol particle size and complex refractive index (RI), which will affect haze formation and global climate change. The potential contributions of ultrafine particles to the atmospheric optical characteristics and to haze spreading cannot be ignored because of their high particle number concentrations and strong diffusibility; measurement of the optical properties of wet ultrafine particles is thus highly important for environmental assessment. Therefore, a surface plasmon resonance microscopy with azimuthal rotation illumination (SPRM-ARI) system is designed to determine the RIs of single particle aerosols with diameters of less than 100 nm in the hygroscopic growth process. Measurements are taken using mixed single particles with different mass ratios. The RIs of mixed single aerosols at different RHs are retrieved by measuring the scattering light intensity using the SPRM-ARI system and almost all the RIs of the bicomponent particles with different mass ratios decrease with increasing water content under high RH conditions. Finally, for each of the bicomponent particles, the maximum standard deviations for the retrieved RI values are only 2.06×10-3, 3.08×10-3 and 3.83×10-3, corresponding to the NaCl and NaNO3 bicomponent particles with a 3:1 mass ratio at 76.0% RH, the NaCl and glucose particles with a 1:3 mass ratio at 89.0% RH, and the NaCl and OA particles with a 1:1 mass ratio at 78.0% RH, respectively; these results indicate that the high-sensitivity SPRM-ARI system can measure the RI effectively and accurately.

Atmospheric environment monitoring technology and equipment in China: A review and outlook.

Accurate monitoring of the atmospheric environment and its evolution are important for understanding the sources, chemical mechanisms, and transport processes of air pollution and carbon emissions in China, and for regulatory and control purposes. This study gives an overview of atmospheric environment monitoring technology and equipment in China and summarizes the major achievements obtained in recent years. China has made great progress in the development of atmospheric environment monitoring technology and equipment with decades of effort. The manufacturing level of atmospheric environment monitoring equipment and the quality of products have steadily improved, and a technical & production system that can meet the requirements of routine monitoring activities has been initiated. It is expected that domestic atmospheric environment monitoring technology and equipment will be able to meet future demands for routine monitoring activities in China and provide scientific assistance for addressing air pollution problems.

Review on recent progress in on-line monitoring technology for atmospheric pollution source emissions in China.

Emissions from mobile sources and stationary sources contribute to atmospheric pollution in China, and its components, which include ultrafine particles (UFPs), volatile organic compounds (VOCs), and other reactive gases, such as NH3 and NOx, are the most harmful to human health. China has released various regulations and standards to address pollution from mobile and stationary sources. Thus, it is urgent to develop online monitoring technology for atmospheric pollution source emissions. This study provides an overview of the main progress in mobile and stationary source monitoring technology in China and describes the comprehensive application of some typical instruments in vital areas in recent years. These instruments have been applied to monitor emissions from motor vehicles, ships, airports, the chemical industry, and electric power generation. Not only has the level of atmospheric environment monitoring technology and equipment been improving, but relevant regulations and standards have also been constantly updated. Meanwhile, the developed instruments can provide scientific assistance for the successful implementation of regulations. According to the potential problem areas in atmospheric pollution in China, some research hotspots and future trends of atmospheric online monitoring technology are summarized. Furthermore, more advanced atmospheric online monitoring technology will contribute to a comprehensive understanding of atmospheric pollution and improve environmental monitoring capacity.

Characterization of submicron aerosol particles in winter at Albany, New York.

A thorough understanding of chemical composition, particle pH, and pollutant emissions is essential to address the climate and human health effects of atmospheric particles. In this study, we used a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and Scanning Mobility Particle Sizer (SMPS) to characterize the composition of submicron particles. Moreover, we applied the ISORROPIA-II model to analyze the particle acidity effect on the compositional characterization of submicron particles from December 22, 2016 to January 7, 2017 in Albany, New York, USA. The results indicated that aerosols with mobility diameter from SMPS in the range 200-400 nm were the main contributors to the mass during the measurement period. The dominance of organics (47%) and sulfate (16%) was similar to previous observations in the eastern United States in Winter 2015, while the fraction of nitrate (23%) was much higher. Moreover, nitrate could easily form at colder temperatures and lower RH levels even when there were more acidic particle periods during the measurement period in Albany. The ISORROPIA-II model indicated that there were more acidic particles, which was estimated using pH values. Lower temperature conditions tended to favor nitrate formation. The nitrate concentration exceeded that of sulfate in the measurement period, even though the SO2 and NOx emissions were similar. The organics in submicron particles were strongly influenced by the local emissions in winter. However, the inorganic compounds in submicron particles could be derived from regional transport as their pollution sources originated from different directions. This may help strategize emission reductions in the future.

Real-world gaseous emission characteristics of natural gas heavy-duty sanitation trucks.

As compared to conventional diesel heavy-duty vehicles, natural gas vehicles have been proved to be more eco-friendly due to their lower production of greenhouse gas and pollutant emissions, which are causing enormous adverse effects on global warming and air pollution. However, natural gas vehicles were rarely studied before, especially through on-road measurements. In this study, a portable emission measurement system (PEMS) was employed to investigate the real-world emissions of nitrogen oxides (NOx) (nitrogen monoxide (NO), nitrogen dioxide (NO2)), total hydrocarbons (THC), carbon monoxide (CO), and carbon dioxide (CO2) from two liquified natural gas (LNG) China V heavy-duty cleaning sanitation trucks with different weight. Associated with the more aggressive driving behaviors, the vehicle with lower weight exhibited higher CO2 (3%) but lower NOx (48.3%) (NO2 (78.2%) and NO (29.4%)), CO (44.8%), and THC (3.7%) emission factors. Aggressive driving behaviors were also favorable to the production of THC, especially those in the medium-speed range but significantly negative to the production of CO and NO2, especially those in the low-speed range with high engine load. In particular, the emission rate ratio of NO2/NO decreased with the increase of speed/scaled tractive power in different speed ranges.

In Situ Quantitative Observation of Hygroscopic Growth of Single Nanoparticle Aerosol by Surface Plasmon Resonance Microscopy.

Aerosol particle hygroscopicity is an important factor in visibility reduction, cloud formation, radiation forcing, and the global climate. The high number concentration of nanoparticles (defined as particles with diameters below 100 nm) means that their hygroscopic growth abilities and potential contributions to the climate and environment are significant. Therefore, a rapid and accurate in situ analysis method for single nanoparticle hygroscopic growth in an atmospheric environment is important to characterize the effects of the particle's physical and chemical properties in this process. In this work, surface plasmon resonance microscopy with azimuthal rotation illumination (SPRM-ARI) is used to observe the hygroscopic growth and water content of single nanoparticles in situ. The hygroscopic growth results of a single-component nanoparticle are well matched with the extended aerosol inorganic model (E-AIM) results, and the proposed method remains reliable even when the relative humidity (RH) exceeds 90%. For a bicomponent nanoparticle (with NaCl as the primary content), the presence of a component without deliquescence phase transitions under increasing humidity conditions causes the measured data to differ from both the Zdanovskii-Stokes-Robinson (ZSR) model and E-AIM predictions in the low RH range. However, because of their complete liquefaction, the growth factor (GF) variation of the bicomponent nanoparticle is close to the model predictions in the high RH range. Finally, based on the positive correlation between particle volume and the gray intensity of SPRM-ARI, GF values can be obtained from the cube root of the gray intensity and the actual water content of single nanoparticles can then be derived.

Simulation of three-stage operating temperature for supersaturation water-based condensational growth tube.

In order to realize accurate dynamic control of supersaturation and to study condensation growth characteristics of nanoparticles through different levels of supersaturation, a series of parametric analyses and systematic comparisons between two-stage and three-stage operating temperature designs were simulated with COMSOL Multiphysics. The simulation results showed that the three-stage operating temperature did not change peak supersaturation compared with two operating temperatures, and the three-stage operating temperature was superior in decreasing the amount of water vapor and the temperature, thus lowering particle loss and variation in detection and collection. The peak supersaturation level increased by 0.3 as the flow rate increased from 0.6 to 2.0 L/min, but the supersaturation peak moved from 0.0027 z0 to 0.08 z0 (i.e., the growth time and the final size decreased by 40%). Peak supersaturation increased as the temperature difference increased or the temperature difference window was shifting left, and minimum activation size decreased. Shifting the 70°C temperature difference window from 9°C, 79°C-1°C, 71°C for the condenser and initiator temperatures resulted in peak supersaturation in the centerline being above 5.8, and the activation size changed as low as 1 nm. Experiments with flow rates varying by a factor of 2.5 (from 0.6 to 1.5 L/min) resulted in a final size decrease of 43% (from 3.2 to 1.8 µm), and experimental results of outlet particle size distributions were equivalent with theoretical analysis as the operating temperature was changed.

Development of a static test apparatus for evaluating the performance of three PM2.5 separators commonly used in China.

PM2.5 separator directly affects the accuracy of PM2.5 sampling. The specification testing and evaluation for PM2.5 separator is particularly important, especially under China's wide variation of terrain and climate. In this study, first a static test apparatus based on polydisperse aerosol was established and calibrated to evaluate the performance of the PM2.5 separators. A uniform mixing chamber was developed to make particles mix completely. The aerosol concentration relative standard deviations of three test points at the same horizontal chamber position were less than 0.57%, and the particle size distribution obeyed logarithmic normal distribution with an R2 of 0.996. The flow rate deviation between the measurement and the set point flow rate agreed to within ±1.0% in the range of -40 to 50°C. Secondly, the separation, flow and loading characteristics of three cyclone separators (VSCC-A, SCC-A and SCC112) were evaluated using this system. The results showed that the 50% cutoff sizes (D50) of the three cyclones were 2.48, 2.47 and 2.44 µm when worked at the manufacturer's recommended flow rates, respectively. The geometric standard deviation (GSD) of the capture efficiency of VSCC-A was 1.23, showed a slightly sharper than SCC-A (GSD =1.27), while the SCC112 did not meet the relevant indicator (GSD = 1.2 ±â€¯0.1) with a GSD = 1.44. The flow rate and loading test had a great effect on D50, while the GSD remained almost the same as before. In addition, the maintenance frequency under different air pollution conditions of the cyclones was summarized according to the loading test.

Development of respirable virtual-cyclone samplers.

Health-based aerosol sampling should reflect how particles penetrate and deposit in various regions of the human respiratory system. Therefore, size-selective sampling should be adopted when monitoring aerosol concentration in the atmosphere. However, cyclone samplers, the most commonly used respirable sampler type in the workplace, show specific particle size-dependent bias toward the international respirable convention. Additionally, cyclone samplers are vulnerable to the dust loading effect resulting in an underestimation of respirable particulate matter. In the previous study, a virtual cyclone has been employed to overcome the dust loading effect, but still had the disadvantage of high aerosol penetration of large particle sizes. Therefore, in this work, the effects of key dimensions of virtual cyclones including chamber width (or inlet width), chamber size and inlet height on the separation performance were further studied and the configurations of virtual cyclones were modified to best fit the ISO/CEN/ACGIH respirable convention. Experimental results demonstrated that a better match with the ISO/CEN/ACGIH respirable convention curve can be achieved by increasing the chamber width to over 20 mm. Moreover, the new virtual cyclones can operate at a flow rate up to 21.5 L/min to collect more respirable particulate matter for the increasingly stringent respirable dust standards. The new virtual cyclones demonstrate accurate and constant measurement of the respirable dust for exposure assessment.

Full-circle range and microradian resolution angle measurement using the orthogonal mirror self-mixing interferometry.

The self-mixing technique based on the traditional reflecting mirror has been demonstrated with great merit for angle sensing applications. In order to solve the problems of the narrow measurement angle range and low resolution in traditional angle measurement method, we proposed an angle measurement system using orthogonal mirror self-mixing interferometry combine an orthogonal mirror with designed mechanical linkage. It overcomes the shortcomings of traditional angle measurement methods and realized the angle measurement with microradian resolution in a full-circle range of 0 rad to 2π rad. In the experiment, the measurement resolution can reach to 5.27 µrad and the absolute error can lower to ± 0.011µrad, which satisfies the requirements of most high accuracy angle measurement.

On the Performance of an Aerosol Electrometer with Enhanced Detection Limit.

An aerosol electrometer with enhanced detection limit was developed for measuring the collected particles electrical current ranging from -50 pA to 50 pA with no range switching necessary. The detection limit was enhanced by suppressing the electric current measurement noise and improving the detection efficiency. A theoretical model for the aerosol electrometer has been established to investigate the noise effect factors and verified experimentally. The model showed that the noise was a function of ambient temperature, and it was affected by the characteristics of feedback resistor and operational amplifier simultaneously. The Faraday cup structure of the aerosol electrometer was optimized by adopting a newly designed cup-shaped metal filter which increased the surface area of the cup; thus the particle interception efficiency was improved. The aerosol electrometer performance-linearity, noise and the particle detection efficiency, were evaluated experimentally. When compared with TSI-3068B, a 99.4% ( R 2 ) statistical correlation was achieved. The results also showed that the root mean square noise and the peak-to-peak noise were 0.31 fA and 1.55 fA, respectively. The particle detection efficiency was greater than 99.3% when measuring particle diameter larger than 7.0 nm.

Design and Evaluation of an Aerosol Electrometer with Low Noise and a Wide Dynamic Range.

A low-noise aerosol electrometer with a wide dynamic range has been designed for measuring the total net charge on high concentration aerosol particles within the range of -500 pA to +500 pA. The performance of the aerosol electrometer was evaluated by a series of experiments to determine linearity, sensitivity and noise. The relative errors were controlled within 5.0%, 1.0% and 0.3% at the range of -40 pA to +40 pA, ±40 pA to ±100 pA, and ±100 pA to ±500 pA respectively. The stability of the designed aerosol electrometer was found to be highly sensitive to temperature variations, but under temperature control, the root mean square noise and the peak-to-peak noise were 1.040 fA and 5.2 fA respectively, which are very close to the calculated theoretical limit of the current noise. The excellent correlation and the advantage of a wide dynamic range have been demonstrated by comparing with the designed aerosol electrometer to a commercial aerosol electrometer. A 99.7% (R²) statistical correlation was obtained; meanwhile, the designed aerosol electrometer operated well even when an overrange phenomenon appeared in the commercial aerosol electrometer.

Comparative study of cylindrical and parallel-plate electrophoretic separations for the removal of ions and sub-23 nm particles.

Cylindrical and parallel-plate electrophoretic separations for the removal of ions and sub-23 nm particles were compared in this study. First, COMSOL Multiphysics® software was utilized to simulate the ion and particle trajectories inside both electrophoretic separations. The results show that ions and sub-23 nm particles are removed simultaneously and that all particles can pass through both electrophoretic separations smoothly at a trap voltage of 25 V. The experimental results show that ion losses become smaller with increasing ion flow rates, and ion losses of the cylindrical and parallel-plate electrophoretic separations range from 56.2 to 71.6% and from 43.8 to 59.6%, respectively, at ion flow rates ranging from 1-3 L/min. For the removal of ions and sub-23 nm particles, the collection efficiency of both electrophoretic separations can reach 100%, but the parallel-plate electrophoretic separation requires a lower trap voltage. The particle loss of the parallel-plate electrophoretic separation is under approximately 10%, which is lower than that of the cylindrical electrophoretic separation. In particular, for large particles (800-2500 nm), the particle losses inside the cylindrical electrophoretic separation are approximately two times higher than those inside the parallel-plate electrophoretic separation. The parallel-plate electrophoretic separation is beneficial for the removal of ions and sub-23 nm particles.

Identification of long-range transport pathways and potential sources of PM2.5 and PM10 in Beijing from 2014 to 2015.

Trajectory clustering, potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) methods were applied to investigate the transport pathways and identify potential sources of PM2.5 and PM10 in different seasons from June 2014 to May 2015 in Beijing. The cluster analyses showed that Beijing was affected by trajectories from the south and southeast in summer and autumn. In winter and spring, Beijing was not only affected by the trajectories from the south and southeast, but was also affected by trajectories from the north and northwest. In addition, the analyses of the pressure profile of backward trajectories showed that backward trajectories, which have important influence on Beijing, were mainly distributed above 970hPa in summer and autumn and below 950hPa in spring and winter. This indicates that PM2.5 and PM10 were strongly affected by the near surface air masses in summer and autumn and by high altitude air masses in winter and spring. Results of PSCF and CWT analyses showed that the largest potential source areas were identified in spring, followed by winter and autumn, then summer. In addition, potential source regions of PM10 were similar to those of PM2.5. There were a clear seasonal and spatial variation of the potential source areas of Beijing and the airflow in the horizontal and vertical directions. Therefore, more effective regional emission reduction measures in Beijing's surrounding provinces should be implemented to reduce emissions of regional sources in different seasons.

All-Fiber Configuration Laser Self-Mixing Doppler Velocimeter Based on Distributed Feedback Fiber Laser.

In this paper, a novel velocimeter based on laser self-mixing Doppler technology has been developed for speed measurement. The laser employed in our experiment is a distributed feedback (DFB) fiber laser, which is an all-fiber structure using only one Fiber Bragg Grating to realize optical feedback and wavelength selection. Self-mixing interference for optical velocity sensing is experimentally investigated in this novel system, and the experimental results show that the Doppler frequency is linearly proportional to the velocity of a moving target, which agrees with the theoretical analysis commendably. In our experimental system, the velocity measurement can be achieved in the range of 3.58 mm/s-2216 mm/s with a relative error under one percent, demonstrating that our novel all-fiber configuration velocimeter can implement wide-range velocity measurements with high accuracy.

A kinetic model for heterogeneous condensation of vapor on an insoluble spherical particle.

A kinetic model is developed to describe the heterogeneous condensation of vapor on an insoluble spherical particle. This new model considers two mechanisms of cluster growth: direct addition of water molecules from the vapor and surface diffusion of adsorbed water molecules on the particle. The effect of line tension is also included in the model. For the first time, the exact expression of evaporation coefficient is derived for heterogeneous condensation of vapor on an insoluble spherical particle by using the detailed balance. The obtained expression of evaporation coefficient is proved to be also correct in the homogeneous condensation and the heterogeneous condensation on a planar solid surface. The contributions of the two mechanisms to heterogeneous condensation including the effect of line tension are evaluated and analysed. It is found that the cluster growth via surface diffusion of adsorbed water molecules on the particle is more important than the direct addition from the vapor. As an example of our model applications, the growth rate of the cap shaped droplet on the insoluble spherical particle is derived. Our evaluation shows that the growth rate of droplet in heterogeneous condensation is larger than that in homogeneous condensation. These results indicate that an explicit kinetic model is benefit to the study of heterogeneous condensation on an insoluble spherical particle.

Development of a multi-stage fog droplet screening system based on the virtual impact principle.

Accurately measuring fog droplet spectra is essential for understanding fog's formation, dissipation, and composition, which makes a challenge to the performance of droplet sampling and measurement systems. Standard particles such as glass beads are widely used to characterize their performance. However, the disparities between glass beads and fog droplets, including refractivity, size distribution, and composition, may lead to calibration errors. In this context, we developed a three-stage fog droplet screening system based on the virtual impact principle. We determined the Stokes number and the diameter of the acceleration nozzle through theoretical analysis. Subsequently, we utilized the computational fluid dynamics software Fluent to explore the influence of key system parameters on screening efficiency, including the diameter of the collection nozzle (D1) and the distance between the acceleration nozzle and the collection nozzle (S). The simulation results indicated that the screening efficiency improved with S. The best performance was achieved when D1 = 1.35 D0 and S = 1.90 D0 (where D0 represents the diameter of the acceleration nozzle), resulting in an average screening efficiency of 75.4%. Finally, we conducted experiments to validate the effectiveness of the screening system. The screening efficiency of each outlet was estimated at 42.2%, 66.1%, 84.0%, and 95.3%, with differences of 2.0%, 3.3%, 4.1%, and 4.7% compared to the simulations. The average screening efficiency was 71.9%, with a deviation of 3.5% from the simulation. These findings demonstrated that the screening system could provide an alternative technical apparatus for characterizing droplet sampling and measurement systems.

High-accuracy fiber optical microphone in a DBR fiber laser based on a nanothick silver diaphragm by self-mixing technique.

A high-accuracy fiber optical microphone (FOM) is first applied by self-mixing technique in a DBR fiber laser based on a nanothick silver diaphragm. The nanothick silver diaphragm fabricated by the convenient and low cost electroless plating method is functioned as sensing diaphragm due to critically susceptible to the air vibration. Simultaneously, micro-vibration theory model of self-mixing interference fiber optical microphone is deduced based on quasi-analytical method. The dynamic property to frequencies and amplitudes are experimentally carried out to characterize the fabricated FOM and also the reproduced sound of news and music can clearly meet the ear of the people which shows the technique proposed in this paper guarantee steady, high signal-noise ratio operation and outstanding accuracy in the DBR fiber laser which is potential to medical and security applications such as real-time voice reproduction for throat and voiceprint verification.