Characterization Of Aerosol Particles Research Articles

A versatile sample-delivery system for X-ray photoelectron spectroscopy of in-flight aerosols and free nanoparticles at MAX IV Laboratory.

Aerosol science is of utmost importance for both climate and public health research, and in recent years X-ray techniques have proven effective tools for aerosol-particle characterization. To date, such methods have often involved the study of particles collected onto a substrate, but a high photon flux may cause radiation damage to such deposited particles and volatile components can potentially react with the surrounding environment after sampling. These and many other factors make studies on collected aerosol particles challenging. Therefore, a new aerosol sample-delivery system dedicated to X-ray photoelectron spectroscopy studies of aerosol particles and gas molecules in-flight has been developed at the MAX IV Laboratory. The aerosol particles are brought from atmospheric pressure to vacuum in a continuous flow, ensuring that the sample is constantly renewed, thus avoiding radiation damage, and allowing measurements on the true unsupported aerosol. At the same time, available gas molecules can be used for energy calibration and to study gas-particle partitioning. The design features of the aerosol sample-delivery system and important information on the operation procedures are described in detail here. Furthermore, to demonstrate the experimental range of the aerosol sample-delivery system, results from aerosol particles of different shape, size and composition are presented, including inorganic atmospheric aerosols, secondary organic aerosols and engineered nanoparticles.

Simulation Analysis on the Characteristics of Aerosol Particles to Inhibit the Infrared Radiation of Exhaust Plumes.

Aerosol infrared stealth technology is a highly effective method to reduce the intensity of infrared radiation by releasing aerosol particles around the hot exhaust plume. This paper uses a Computational Fluid Dynamics (CFD) two-phase flow model to simulate the exhaust plume fields of three kinds of engine nozzles containing aerosol particles. The Planck-weighted narrow spectral band gas model and the Reverse Monte Carlo method are used for infrared radiation transfer calculations to analyze the influencing factors and laws for the suppression of the infrared radiation properties of exhaust plumes by four typical aerosol particles. The simulation calculation results show that the radiation suppression efficiency of aerosol particles on the exhaust plume reaches its maximum value at a detection angle (ϕ) of 0° and decreases with increasing ϕ, reaching its minimum value at 90°. Reducing the aerosol particle size and increasing the aerosol mass flux can enhance the suppression effect. In the exhaust plume studied in this paper, the radiation suppression effect is best when the particle size is 1 μm and the mass flux is 0.08 kg/s. In addition, the inhibition of aerosol particles varies among different materials, with graphite having the best inhibition effect, followed by H2O, MgO, and SiO2. Solid particles will increase the radiation intensity and change the spectral radiation characteristics of the exhaust plume at detection angles close to the vertical nozzle axis due to the scattering effect. Finally, this paper analyzed the suppression effects of three standard nozzle configurations under the same aerosol particle condition and found that the S-bend nozzle provides better suppression.

Measurement report: Evaluation of the TOF-ACSM-CV for PM1.0 and PM2.5 measurements during the RITA-2021 field campaign

Abstract. The recently developed time-of-flight aerosol chemical speciation monitor with a capture vaporizer and a PM2.5 aerodynamic lens (TOF-ACSM-CV-PM2.5) aims to improve the collection efficiency and chemical characterization of aerosol particles with a diameter smaller than 2.5 µm. In this study, comprehensive cross-comparisons were performed between real-time online measurements and offline filter analysis with 24 h collection time. The goal was to evaluate the capabilities of the TOF-ACSM-CV-PM2.5 lens, as well as the accuracy of the TOF-ACSM-CV-PM2.5. The experiments were conducted at Cabauw Experimental Site for Atmospheric Research (CESAR) during the RITA-2021 campaign. The non-refractory fine particulate matter (PM1.0 and PM2.5) was measured by two collocated TOF-ACSM-CV-PM2.5 instruments by placing them behind a PM2.5 and PM1.0 inlet, respectively. A comparison between the ACSMs and PM2.5 and PM1.0 filter samples showed a much better accuracy than ±30 % less given in the previous reports, with average differences less than ±10 % for all inorganic chemical species. In addition, the ACSMs were compared to the Monitoring Instrument for Aerosol and Gas (MARGA) (slope between 0.78 and 0.97 for inorganic compounds, R2≥ 0.93) and a mobility particle size spectrometer (MPSS), measuring the particle size distribution from around 10 to 800 nm (slope was around 1.00, R2= 0.91). The intercomparison of the online measurements and the comparison between the online and offline measurements indicated a low bias (< 10 % for inorganic compounds) and demonstrated the high accuracy and stability of the TOF-ACSM-CV-PM2.5 lens for the atmospheric observations of particle matter. The two ACSMs exhibited an excellent agreement, with differences less than 7 %, which allowed a quantitative estimate of PM1.0 vs. PM2.5 chemical composition. The result showed that the PM1.0 accounted for about 70 %–80 % of the PM2.5 on average. The NO3 mass fraction increased, but the organic carbon (OC) mass fraction decreased from PM1.0 to PM2.5, indicating the size dependence on chemical composition.

Molecular dynamics investigation on structural and interfacial characteristics of aerosol particles containing mixed organic components

Microscopic morphology plays a significant role in the description of aerosol particle evolution, but the knowledge on particles containing mixed organic matters is insufficient. In this study, molecular simulation (MD) method is employed to investigate the morphologies of particles containing two or three of malonic acid (MA), adipic acid (AA) and eicosane (C20). The key point is the effects of organic species and water content on structural and interfacial characteristics of particles. Results show that all dry particles exhibit the approximate core-shell structure with the shell composed of organic with longer hydrocarbon chain. With water content increasing from 100 to 1000, MA + AA + H2O particles present the core-shell structure with decreasing MA in the core, while particles containing C20 successively exhibit the core-shell structure and the ball-cap structure with three layers. These structural differences are caused by the surface propensity of organics, which is positively correlated with both the length of hydrocarbon chain and the water content. At the particle surface, hydrophobic groups of organic molecules direct towards the gas phase. MA (AA) located between water droplet and C20 cluster orient their hydrophobic groups toward C20. Furthermore, ratios of hydrophilic and hydrophobic atoms (K) at the surface of all studied particles increases with increasing water content, and at each water content the order is K(MA + AA) > K(MA + AA + C20) > K(AA + C20) > K(MA + C20). These findings provide microscopic information support for the development of theoretical model for the particle formation and growth.

Influence of temperature and humidity on scattering characteristics of aerosol particles in the terahertz band.

The terahertz band is considered to be the next breakthrough point to revolutionize communication technology, attributed to its rich spectrum resources. The study of terahertz atmospheric transmission characteristics is important in guiding the terahertz communication window selection process. In this report, based on the equivalent medium theory, the scattering characteristics of terahertz Gaussian beams by moist media are discussed. Numerical results show that the extinction coefficient of particles is mainly affected by the humidity, and the scattering efficiency is affected by both temperature and humidity. When the temperature is over 273K and the humidity is 0.5, the extinction efficiency shows a trend of increasing initially and decreasing afterwards. Hence, the appropriate temperature is beneficial to minimizing the attenuation coefficient.

Influence of the Sphericity Coefficient on the Deposition Characteristics of Aerosol Particles on the Surface of Photovoltaic (PV) Modules: Numerical Simulation

The deposition of aerosol particles has a significant impact on the output capacity of photovoltaic modules. Therefore, studying the deposition characteristics of aerosol particles on photovoltaic modules is of great importance for improving their output capacity. Particle morphology is one of the important parameters affecting the deposition characteristics of aerosol particles. This study introduces the spherical coefficient as a quantification method for characterizing the morphology of aerosol particles. Numerical simulations using FLUENT 2022 software were conducted to investigate the influence of the spherical coefficient on the deposition characteristics of aerosol particles on photovoltaic modules. The reliability of the numerical simulations was further validated through experimental studies. Based on the research, the following conclusions can be drawn: the airflow velocity near the surface of the photovoltaic panel increases from bottom to top, with the lowest wind speed recorded near the ground at a minimum value of 2.2 m/s and a maximum value of 3.89 m/s. The air pressure near the surface of the photovoltaic panel shows a decreasing trend from bottom to top, with the highest pressure recorded near the ground at a maximum value of 10 pa and a minimum value ranging from 3.33~5.56 pa. During the deposition process, the accumulation of particles increases with an increase in the sphericity factor. Furthermore, as the sphericity factor gradually increases, the distribution of particles on the surface of the photovoltaic panel becomes more dispersed, covering the entire surface.

Characterization of atmospheric aerosols by SEM-EDX in a rural-continental environment-a seasonal approach

The vital information on the morphology and composition of the atmospheric aerosols over any region is critical to understand their climatic and health effects. This work aims at the physicochemical characteristics of atmospheric aerosols at a rural continental site in northeastern India. We collected the aerosol samples from January to December 2018 and applied a seasonal approach to investigate the physical and elemental characteristics of aerosol particles. A Scanning Electron Microscope (SEM) has been used to examine the morphology of particles that, includes shape, size, and structure information. Energy-dispersive X-ray analysis (EDX) is used to investigate the elemental composition information. By using the SEM-EDX, we have noticed a variation in the morphology of particles and elemental composition from season to season. The different particle shapes vary from regular to irregular, including spherical, nearly spherical, triangular, capsule-like, and platy shapes have been observed. We have seen a variety of particle clusters, including chain-like structures, porous textures, soot structures, and irregular structures. A size range of particles with a diameter ranging from 100 nm to 30 µm has been observed. The presence of elements C, Si, O, B, K, Ca, P, S, Fe, Na, N, Cl, Mg, and Al has been examined in different seasons. We have noticed that road dust, crustal origin particles, and carbonaceous particles dominate the study region. We have observed a clear seasonal variation in the percentage of different elements. A small contribution by sea salt origin elements has also been noticed during the pre, monsoon, and post-monsoon seasons when winds flow from the marine region, and air mass back trajectory results support this.

Numerical simulation of welding aerosol diffusion based on plasma flow characteristics

The welding plasma flow and the turbulent diffusion of aerosol were explored in this study to describe the diffusion of welding aerosol particles more accurately. A new simulation method for welding aerosol pollution sources was applied in this study based on considering the momentum transfer between multiphase flows. The effect of distance and angle between welded electrodes on plasma flow was evaluated through CFD numerical simulation and visualization experiment. The changes in the initial positions of welding aerosol particles under different plasma morphological characteristics were evaluated. The action mechanism of the local flow field on aerosol particle trajectory was evaluated under different working conditions. Finally, the diffusion characteristics of aerosol particles with different particle sizes were explored. The results showed that the distance and angle between the anode and the cathode of the welding affected the plasma flow morphology and stability, and thus affecting the diffusion trajectory of aerosol particles. The effect increased when the distance to the welding spot was small. The proportion of particles that diffused to quadrants II and III increases from 50% to 87.4% when the polar angle decreased from 90° to 30°. Particles with particle size over 1μm had the highest airflow dispersion, and their RDR was up to 71, whereas those with a particle size less than 0.15μm had an RDR of 49 due to the effect of Brownian motion and molecular slip.

Aerosol infrared stealth technology: Theory and development of infrared suppression and particle dispersion in aircraft plume

Aerosol infrared stealth technology (AIRST) is a highly effective method to suppress the strong infrared (IR) signal and interfere in the IR detection within a short time. It has been equipped on many low-speed vehicles, such as tanks and helicopters. The researchers have conducted many experimental and numerical investigations on the AIRST applied in the jet engine. The recent two decades have witnessed the rapid development of the particle IR extinction and aerosol IR suppression in aircraft plume. This paper has reviewed the published studies about the AIRST comprehensively, including the IR extinction of a discrete particle, IR radiation suppression characteristics of aerosol clusters, and distribution patterns of aerosol particles. The widely applied theories of particle IR extinction and its applicability have been analysed, as well as the characteristics and influence factors of the particle IR extinction. This paper has summarized the mostly used calculation model for IR transmittance of aerosol particle clusters and the IR suppression characteristics of aerosol particles in aircraft plume. In addition, the effects of aerosol injection on the aerosol particle dispersion and turbulent flow features have been systematically displayed. Finally, the future challenges and suggestions about the AIRST are discussed, which could be valuable for the aerosol IR suppression and its application on the supersonic aircrafts.

The use of transmission electron microscopy with scanning mobility particle size spectrometry for an enhanced understanding of the physical characteristics of aerosol particles generated with a flow tube reactor

Aerosol particles are found throughout the atmosphere with considerable variety in morphological characteristics and chemical composition. Identifying and characterizing these particle attributes is a significant step toward improving our understanding of atmospheric chemistry. Many methods exist for measuring the size and spreading of Aitken mode particles, but there are few studies rigorously comparing the results generated between approaches in this field. Here, we compare two methods for assessing aerosol particles – scanning mobility particle size spectrometry (SMPS) and transmission electron microscopy (TEM). Aitken mode particles consisting of salt seed particles and seed particles coated with α-pinene secondary organic material were produced in a flow tube reactor. The same populations of particles were analyzed using both techniques to facilitate direct comparison. For ammonium sulfate particles impacted onto carbon and Si TEM substrates, diameters increased by +0% to +30% when compared to the suspended electrical mobility diameters, an unexpectedly wide range for a single component system. Coated particles had unpredictable diameter differences, sometimes evaluated at larger and sometimes smaller sizes after impaction when compared to the corresponding SMPS electrical mobility diameter, from −34% to +60%. While all particles were generally round in shape, variation in particle morphology was also observed in coated samples. Between 0% and 98% of particles displayed obvious phase separation suggesting more population-level diversity than expected from these particle generation processes. Characterizing the differences between TEM and SMPS results better elucidates the role of a substrate where present and shows nonequivalence in particle size distributions obtained from different instruments.Copyright © 2023 American Association for Aerosol Research

Effect of Oily Aerosol Charge Characteristics on the Filtration Efficiency of an Electrostatically Enhanced Fibrous Filter System

The synergistic effect of electrostatically enhanced fibrous filtration originates from the charging characteristics of aerosol particles and electret fibers in an electric field. Two electrostatically enhanced fibrous filter systems are designed in this study to investigate the mechanism of the effects of the charging characteristics of oily aerosol on the filtration efficiency. We investigate the charging characteristics and their effects on the filtration efficiency of dioctyl-phthalate (DOP) aerosol particles of various sizes by setting different filter systems and electric field intensities. The experimental results show that the charge of DOP particles increases with the strength of the electric field, and the average charge increases with the particle size. The maximum charge of DOP particles reaches 4760 eC/P, and the filtration efficiency of the coupled system improves when DOP particles are amply charged. For 0.25 μm DOP particles as the most penetrating particle size, the system had good long-term stability, and the filtration efficiency is approximately 72% higher than that of the fiber acting alone. Meanwhile, the problem of oily aerosol deposition reducing the electret filtration efficiency is solved, providing a basis for long-term filtration and oily aerosol purification by electret fiber.

Particle beam deflection imaging for simultaneous characterization of aerosol particle size and charge

We present a novel method referred to as Particle Beam Deflection Imaging (PBDI) for the simultaneous characterization of the size and electric charge distribution of submicrometer (currently ∼200–800 nm) aerosol particles in real-time (currently ≤30 s). It combines aerodynamic and electrostatic particle deflection, providing two-dimensional information on size and charge in a single two-dimensional light scattering image. The image allows one to extract information on charge-averaged and charged-resolved particle size distributions, and on size-dependent bipolar charge distributions. The current prototype has a size resolution of <50 nm and can resolve individual charge states. Compared to Scanning Mobility Particles Sizers (SMPS), the PBDI offers the advantage of providing simultaneous size and charge information at higher size resolution in a significantly shorter measurement time, hence allowing real-time characterization of volatile aerosol particles.

A Collection of Molecular Fingerprints of Single Aerosol Particles in Air for Potential Identification and Detection Using Optical Trapping-Raman Spectroscopy.

Characterization, identification, and detection of aerosol particles in their native atmospheric states remain a challenge. Recently, optical trapping-Raman spectroscopy (OT-RS) has been developed and demonstrated for characterization of single, airborne particles. Such particles in different chemical groups have been characterized by OT-RS in recent years and many more are being studied. In this work, we collected single-particle Raman spectra measured using the OT-RS technique and began construction of a library of OT-RS fingerprints that may be used as a reference for potential detection and identification of aerosol particles in the atmosphere. We collected OT-RS fingerprints of aerosol particles from eight different categories including carbons, bioaerosols (pollens, fungi, vitamins, spores), dusts, biological warfare agent surrogates, etc. Among the eight categories, spectral fingerprints of six groups of aerosol particles have been published previously and two other groups are new. We also discussed challenges, limitations, and advantages of using single-particle optical trapping-Raman spectroscopy for aerosol-particle characterization, identification, and detection.

Characterization of aerosol particles containing trace elements (Ga, As, Rb, Mo, Cd, Cs, Tl, and others) and their atmospheric concentrations with a high temporal resolution

Particles with diameters of 2.5 μm and smaller (PM2.5) contain various trace elements and potentially influence human health. Physical and chemical features of individual particles and their concentrations with detailed time trends provide useful information for an accurate estimation of the sources and potential toxicity of PM2.5. Although many studies have measured these features for relatively common elements (e.g., Fe, Zn, and Pb), diurnally concentrations changes and mixing states of particles containing trace elements (below 1 ng m−3) have not been explicitly analyzed. In this study, we observed atmospheric concentrations of 44 elements in PM2.5 using a real-time observation technique (GED-ICP-MS) at Fukuoka, western Japan, during the winter and spring of 2018. As a result, various elements were detected in anthropogenic air masses from long-range transports. We also sampled aerosol particles every 3 h and analyzed their shapes, mixing states, and compositions using transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy to demonstrate particle occurrences containing trace elements at an individual scale. We especially focused on the abundance and physicochemical features of aerosol particles containing trace elements, such as As, Ga, Rb, Mo, Cd, Cs, and Tl. The element group Ga, Rb, and Cs and a pair of As and Cd showed significant correlations and we succeeded to observe three Ga-bearing particles, seven As-bearing particles, and three Cd-bearing particles. Moreover, we introduce particle features containing Mo and Tl, which were not reported in previous studies. Our results have implications for understanding the occurrence of trace elements in the atmosphere, identifying aerosol sources, and evaluating the influences of aerosol particles on human health.

Observation Analyses of Aerosol Size Distribution Properties from February to March, 2019 in Tianjin Urban Area

The aerosol size distribution is an important physical parameter reflecting the source, formation process, and pollution characteristics of aerosol particles. In order to study the properties of aerosol number concentration and size distributions in the Tianjin urban area,the aerosol number concentration and size distributions ranging from 10-600 nm were detected using a scanning mobility particle sizer (SMPS) during February and March, 2019. The results showed that in the Tianjin urban area, the aerosol number concentration,surface area concentration. and volume concentration in the size range of 10-600 nm were 22188.22 cm-3, 1581.08 μm2·cm-3, and 70.76 μm3·cm-3,respectively, in late winter and early spring. The aerosol number concentration,surface area concentration, and volume concentration spectrum were all unimodally distributed,and the peak value sizes were 109.40, 269.00, and 429.40 nm. The number concentrations of the nucleation mode (10-20 nm),Aitken mode (20-100 nm), and accumulation mode (100-600 nm) aerosols accounted for 1.40%, 52.44%, and 46.16% of the total number concentration. The diurnal variation in aerosol number concentration showed three peaks (06:00-08:00, 12:00-14:00, and 18:00-20:00) on work days and two peaks (07:00-08:00 and 19:00-21:00) on weekends. The peaks appeared 1-2 hours later on weekends,and the increment of aerosol number concentration was attributed to vehicle exhaust emissions. Meteorological factors had a significant influence on the aerosol size distribution in Tianjin; aerosol number concentration values were high in east and southwest wind. On non-precipitation days,the aerosol number size distribution moved to larger size ranges with the increment of relative humidity (RH); as the RH increased from <20% to 50%-60%,the size peak increased from 50 nm to 131 nm. The precipitation removed 100-200 nm aerosol particles discernibly,which resulted in the size peak decreasing to 98 nm.

Aerosol particle characteristics measured in the United Arab Emirates and their response to mixing in the boundary layer

Abstract. Aerosol particles play an important role in the microphysics of clouds and hence in their likelihood to precipitate. In the changing climate already-dry areas such as the United Arab Emirates (UAE) are predicted to become even drier. Comprehensive observations of the daily and seasonal variation in aerosol particle properties in such locations are required, reducing the uncertainty in such predictions. We analyse observations from a 1-year measurement campaign at a background location in the United Arab Emirates to investigate the properties of aerosol particles in this region, study the impact of boundary layer mixing on background aerosol particle properties measured at the surface, and study the temporal evolution of the aerosol particle cloud formation potential in the region. We used in situ aerosol particle measurements to characterise the aerosol particle composition, size, number, and cloud condensation nuclei (CCN) properties; in situ SO2 measurements as an anthropogenic signature; and a long-range scanning Doppler lidar to provide vertical profiles of the horizontal wind and turbulent properties to monitor the evolution of the boundary layer. Anthropogenic sulfate dominated the aerosol particle mass composition in this location. There was a clear diurnal cycle in the surface wind direction, which had a strong impact on aerosol particle total number concentration, SO2 concentration, and black carbon mass concentration. Local sources were the predominant source of black carbon as concentrations clearly depended on the presence of turbulent mixing, with much higher values during calm nights. The measured concentrations of SO2, instead, were highly dependent on the surface wind direction as well as on the depth of the boundary layer when entrainment from the advected elevated layers occurred. The wind direction at the surface or of the elevated layer suggests that the oil refineries and the cities of Dubai and Abu Dhabi and other coastal conurbations were the remote sources of SO2. We observed new-aerosol-particle formation events almost every day (on 4 d out of 5 on average). Calm nights had the highest CCN number concentrations and lowest κ values and activation fractions. We did not observe any clear dependence of CCN number concentration and κ parameter on the height of the daytime boundary layer, whereas the activation fraction did show a slight increase with increasing boundary layer height due to the change in the shape of the aerosol particle size distribution where the relative portion of larger aerosol particles increased with increasing boundary layer height. We believe that this indicates that size is more important than chemistry for aerosol particle CCN activation at this site. The combination of instrumentation used in this campaign enabled us to identify periods when anthropogenic pollution from remote sources that had been transported in elevated layers was present and had been mixed down to the surface in the growing boundary layer.

Change in spray behavior of pharmaceutical particles by creating bypass hole in dry powder inhaler

This study presents the effects of adding bypass holes in a dry powder inhaler on aerosol particle characteristics. A commercially available inhaler device was modified with bypass holes, and the resulting drug powder spray characteristics were investigated in terms of how the direction, size, and position of the bypass holes in the inhaler passage affect the spray output to find the optimal design. All three factors influenced the aerosol behavior, and in particular, it is most significantly affected by the direction of bypass hole faces. Adding bypass holes to the inhaler passage was found to decrease the mean penetration length of the drug particles by 12%; however, at the same time, the spray angle is increased by 35%, which leads to a significant decrease in forward particle momentum.

Newly designed mouthpiece to improve spray characteristics of pharmaceutical particles in dry powder inhaler

This study presents the effects of mouthpiece designs in carrier-based dry powder inhalation on aerosol particle characteristics. Simulation models are developed to investigate drug powder spray characteristics from mouthpieces of four different-shaped flow channels. The simulation results agree well with the results of two experiments, one involving particle image velocimetry and the other the Anderson cascade impactor. A mouthpiece with a spiral channel and mixing chamber is discovered to be effective for low axial-flow velocities in the forward direction and yielded a more uniform dispersion of particles in the radial direction as the drug particles are ejected through the mouthpiece. This results in more effective delivery of the drug particles to the peripheral target regions of the respiratory system.

Sources and nature of ice-nucleating particles in the free troposphere at Jungfraujoch in winter 2017

Abstract. Primary ice formation in mixed-phase clouds is initiated by a minute subset of the ambient aerosol population, called ice-nucleating particles (INPs). The knowledge about their atmospheric concentration, composition, and source in cloud-relevant environments is still limited. During the 2017 joint INUIT/CLACE (Ice Nuclei research UnIT/CLoud–Aerosol Characterization Experiment) field campaign, observations of INPs as well as of aerosol physical and chemical properties were performed, complemented by source region modeling. This aimed at investigating the nature and sources of INPs. The campaign took place at the High-Altitude Research Station Jungfraujoch (JFJ), a location where mixed-phase clouds frequently occur. Due to its altitude of 3580 m a.s.l., the station is usually located in the lower free troposphere, but it can also receive air masses from terrestrial and marine sources via long-range transport. INP concentrations were quasi-continuously detected with the Horizontal Ice Nucleation Chamber (HINC) under conditions representing the formation of mixed-phase clouds at −31 ∘C. The INP measurements were performed in parallel to aerosol measurements from two single-particle mass spectrometers, the Aircraft-based Laser ABlation Aerosol MAss Spectrometer (ALABAMA) and the laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF). The chemical identity of INPs is inferred by correlating the time series of ion signals measured by the mass spectrometers with the time series of INP measurements. Moreover, our results are complemented by the direct analysis of ice particle residuals (IPRs) by using an ice-selective inlet (Ice-CVI) coupled with the ALABAMA. Mineral dust particles and aged sea spray particles showed the highest correlations with the INP time series. Their role as INPs is further supported by source emission sensitivity analysis using atmospheric transport modeling, which confirmed that air masses were advected from the Sahara and marine environments during times of elevated INP concentrations and ice-active surface site densities. Indeed, the IPR analysis showed that, by number, mineral dust particles dominated the IPR composition (∼58 %), and biological and metallic particles are also found to a smaller extent (∼10 % each). Sea spray particles are also found as IPRs (17 %), and their fraction in the IPRs strongly varied according to the increased presence of small IPRs, which is likely due to an impact from secondary ice crystal formation. This study shows the capability of combining INP concentration measurements with chemical characterization of aerosol particles using single-particle mass spectrometry, source region modeling, and analysis of ice residuals in an environment directly relevant for mixed-phase cloud formation.

Characterization of aerosol particles during a high pollution episode over Mexico City

More than 7 thousand wildfires were recorded over Mexico in 2019, affecting almost 640 thousand hectares. Most of these fires occurred during the spring season generating dense smoke plumes, impacting urban areas in the central part of the Mexican plateau. From May 10 to 17, 2019, biomass burning (BB) plumes affected Mexico City (MC) and diffused across the basin, producing PM2.5 levels ~ 2 times higher than the nation's air quality standards. Average PM2.5 concentrations increased sharply from 29.4 ± 7.2 µg m−3 to 65.1 ± 13.6 µg m−3 when the dense smoke plumes were detected. The higher particle concentration impacted the aerosol optical depth (AOD) as values ~ 3 times greater than the annual mean (0.32 ± 0.12) were measured, which resulted in a 17% loss of global horizontal irradiation (GHI). Under these severe pollution conditions, the visibility (Va) was reduced by ~ 80%. The high incidence of strong absorbent particles, such as soot and tarballs was revealed through electron microscopy and X-ray fluorescence (XRF) analysis. These techniques show chemical similarities between MC aerosols and those from the high-altitude (~ 4010 m. a. g. l.) Altzomoni Atmospheric Observatory, evidencing a strong influence of the BB emissions, suggesting a regional transport of these pollutants.