Search

Atmospheric aerosol contributes significantly to public health and plays a critical role in global climate. Recent laboratory experiments showed that new particle formation is significantly enhance...

The size-resolved chemical composition and mixing state of single particles were observed by using single particle aerosol mass spectrometry (SPAMS) from May 12 to June 8, 2017. A total of 979,899 particles were successfully ionized to identify 6 main particle groups including carbon-rich particles (47.66%), K-rich particles (28.78%), heavy-metal particles (10.12%), sodium particles (8.86%), dust particles (3.89%), and ammonium particles (0.67%). The wind direction and speed had large impacts on the proportion of carbonaceous aerosol particles and had little influence on heavy-metal particles. The relative humidity (RH) had great impacts on the chemical components of aerosol particles. The proportion of secondary particles increased, while the primary particles diminished as RH increased. The proportion of carbon-rich particles decreased with increasing particle size. However, the size distributions varied significantly for different types of carbonaceous particles. Sodium particles and heavy-metal particles were mainly concentrated at sizes larger than 1 μm. K-rich particles had a maximum proportion at 0.5–1.0 μm. The number fraction of ammonium particles predominated chiefly at 0.6–2.0 μm. It has been found that aerosol particles, mainly from burning processes, were mixed with 36 [C 3 ] + to different degrees at Mt. Tai. A high proportion of ammonium particles were mixed with organics and elemental carbon (OCEC), elemental carbon-sulfate (EC-sulfate), and elemental carbon-secondary (EC-secondary) particles, while few of these particles were mixed with EC-nitrate particles, which indicated that the ammonia in the air was inclined to combine with organic species and sulfate. A higher proportion of atmospheric particles mixed with nitrate were observed compared to those mixed with sulfate.

Brake wear particles constitute a significant part of the non-exhaust related particulate matter (PM) associated to traffic. These particles derive from various components of the vehicles’ brake system and were recognized as an important pollution source only recently. In the present study, electron microscopy was applied to elucidate brake wear particle morphology and associated chemical composition. Sampling was carried out on a brake test bench. Particles were collected on 13 successive polycarbonate foil bags and a backup filter by means of a Dekati Low Pressure Impactor (DLPI), based on the equivalent aerodynamic particle diameter. The results revealed a broad size range from the micro-to the nano-scale, as measured on electron microscope images, including coarse (2.5–10 μm), fine (0.1–2.5 μm) and ultrafine ones (

This work presents a comprehensive study of the size-resolved particle hygroscopicity measurements in a suburban ambient in Southern Europe (Madrid). Measurements were obtained by an H-TDMA instrument during a 16-month period for the size particles of 50, 80, 110, 190 and 265 nm. The annual, seasonal and daily patterns were investigated with the aim of characterizing the hygroscopic growth of ambient aerosol particles and their mixing state in the atmosphere. Simultaneously, the particle number size distributions, gaseous species (SO2, NO, NO2, and O3) and meteorological factors were measured and analyzed, complementing this study. The growth factor probability density functions (GF-PDFs) at the measurement site normally exhibit a multimodal pattern with two hygroscopic groups of particles clearly differentiated, indicating that the aerosol particles were externally mixed. Generally, particle hygroscopicity increased as particles were larger, indicating an increase less-to-more hygroscopic species. In cold seasons, aerosol particles were more externally mixed than in warm seasons. Thus, the growth factor of the more hygroscopic particle group (GFMH) was higher than in warm seasons varying from 1.41 (50 nm)-1.70 (265 nm). However, the number fraction of more hygroscopic particle group (NFMH) was lower. The persistence of anticyclonic stagnation conditions and the enhanced particulate nitrate formation from traffic emissions seemed to be the two main factors responsible for this result. A dominant hygroscopic particle group was often observed in warm seasons, due to frequent NPF bursts. In these seasons, and probably associated to the high atmospheric oxidative capacity, the highest average growth factors (GFmean) of the study period were obtained. This finding was also reflected in the diurnal cycle. Thus, GFmean and NFMH during rush-hour periods usually reached the minimum values of the day, especially in cold seasons. When comparing weekdays and weekends, the strong influence of traffic emissions on particle hygroscopicity was evidenced (WKs/WEs ratios for NFMH were

One of the extensively used methods for aerosol mass concentration measurement is the optical filter method used in Aethalometer. Due to the aerosol loading and multi scattering effect, there are uncertainties that can lead to underestimation or overestimation of aerosol concentration and measurement of the absorption coefficient. To overcome such uncertainties, a data correction method has been adopted in the present work. During the winter, pre-monsoon and post-monsoon seasons, Aethalometer underestimated black carbon (BC) concentration by 8 ± 1%, 11 ± 1%, and 10.5 ± 0.2%, due to the higher aerosol deposition. While in the monsoon season, underestimation of 5.5 ± 2% is observed because of the presence of bigger scattering nature aerosol. For 70% of days, found a positive correlation between the compensation parameter (k880) and wavelengths, which indicated the dominance of the smaller aerosol particles. While 30% of days have a negative correlation due to the bigger aerosol particle. In the winter, pre-monsoon and monsoon seasons, the absorption coefficient at 370 nm was 86%, 90%, and 93% higher than that of 880 nm due to the higher biomass burning emissions. The absorption Angstrom exponent (α370-880) was 1.02 for fossil fuel burning and the corresponding k880 was 0.0037. In the winter and post-monsoon seasons, BC emissions from fossil fuel combustion dominated over the BC emitted by biomass burning emissions with α370-880

The hygroscopicity and phase state of atmospheric aerosols, depending on relative humidity (RH), dominate their impacts on global climate and heterogeneous atmospheric chemistry. It is challenging to achieve full course measurements on hygroscopic mass growth factors (MGFs), deliquescence relative humidity (DRH), efflorescence relative humidity (ERH) and efflorescence kinetics of aerosols at different ambient RH, which concerns the gas, liquid and solid phases. The combination of a rapid scan vacuum FTIR and a RH pulsed controlling system allowed us to directly and synchronously determine ambient RH and MGFs of aerosols, as well as nucleation rates in the efflorescence process with a subsecond time resolution. With an excellent signal-to-noise ratio and high time resolution spectra, the vacuum FTIR method allowed for real-time in situ measurements of water partitioning between gas and particle phases as it changed with RH, as well as the ratio between the number of crystallized aerosol droplets and the total number of particles during the efflorescence of aerosols. The hygroscopicity and efflorescence kinetics of NaCl and (NH4)2SO4 aerosols were studied in linear RH change mode and in pulsed RH change mode. The measured MGF values, DRH and ERH agreed well with theoretical data from the Extended Aerosol Inorganic Model (EAIM) and literature for both the linear and pulsed RH change modes. In addition, the pulsed RH mode also provided both heterogeneous and homogeneous nucleation rates for NaCl and (NH4)2SO4 aerosols. There were significant advantages of the vacuum FTIR method combined with the pulsed RH controlling technique. First, the RH was continuously changed and was determined in real-time with a time resolution of 0.12 s in the pulsed mode. During the RH change process, the water content in the aerosols was measured synchronously with the same time resolution, allowing for high-efficiency measurements of MGFs, ERH and DRH. The deviations of measured MGFs from the EAIM predictions in the RH range of 75–55% were less than ±3.3%. Second, FTIR spectroscopy was sensitive to phase transitions, which provided quantitative information on the ratio of the number of aerosols transformed from droplets to solid particles at ERH, allowing for the measurement of nucleation kinetics during the efflorescence of aerosols.

Vape shops are widespread due to the popularity of electronic cigarettes (e-cigs) as an alternative to tobacco cigarettes. In this study, sixty-seven Southern California vape shops were randomly surveyed for building characteristics, ventilation, and business patterns. Based on the survey results, six representative shops were recruited for real-time measurements of indoor and outdoor fine and ultrafine particles concentrations on a busy and less busy day. Occupancy, vaping frequency, and opening and closing of doors were recorded, and shop air exchange rate was determined. Indoor CO2, relative humidity, and temperature were also recorded. In addition, simultaneous measurements were taken at increasing distances away from a vaping area to assess the mixing and spatial profiles of particle levels inside the shops. During active vaping, real-time indoor particle number concentration and gravimetric-corrected PM2.5 mass concentration across the six vape shops varied from 1.3 × 104 to 4.8 × 105 particles/cm3 and from 15.5 to 37,500 μg/m3, respectively. The spatial profiles of particle number and mass were more uniformly mixed than expected in an indoor environment. Total vaping frequency was the main predictor of particle concentrations inside the vape shops when indoor-outdoor particle mass transfer is minimal (doors closed).

Laboratory experiments were conducted to investigate femtosecond filamentation induced particle formation and growth in particle-free air as well as in the presence of pre-existing ammonium sulfate aerosols. The ability of laser induced particles to act as cloud condensation nuclei (CCN) was explored. The influence of water vapor and the pulse energy on the production efficiency and activation properties of particles were also examined. In particle-free air, laser filaments could lead to a significant production of new particles, the number concentration of which was comparable to or larger than that in polluted ambient air, depending upon the pulse energy and humidity. Total particle number and mass concentrations within 20–708 nm were predominantly contributed by particles with a diameter smaller than 100 nm. Remarkably high NOx up to an order of ∼101 ppm was generated in the chamber, allowing sufficient production of HNO3 and probably subsequent HNO3-H2O binary nucleation. In the presence of pre-existing particles, the yield of particle number was largely enhanced in laser filaments, especially in humid air. Particle number size distribution shifted towards smaller particle size, leading to a slight increase in particle mass. It was found that a considerable portion of laser induced particles, no matter generated with or without pre-existing particles, could act as CCN. The amount of CCN at 0.80% supersaturation was in the magnitude of 104∼105 cm−3 in all experiments, nearly one order larger than the average ambient level even in severely polluted regions. Overall, increasing the pulse energy and water vapor would favor particle formation and growth as well as the production of CCN. Raising the pulse energy also resulted in a decline of the hygroscopic parameter κ, implying the modification of aerosol chemical composition. Though more investigative studies are still needed to explore mechanisms underlying some of these experimental results, laser filaments are undoubtedly capable of inducing substantial particle formation and modifying microphysical/chemical properties of pre-existing particles. By influencing these crucial properties and thereby aerosol direct/indirect climatic and environmental effects, laser filamentation would provide a promising potential for related atmospheric applications.

In order to understand the electrostatic charging state of atmospheric hundreds nanometer particles that has particular impact on health, we have observed the atmospheric particles charge distributions intermittently for one year. To easily estimate particle charge distribution, first of all, we have developed a simple instrument and calculation method. We confirmed by comparison with stationary charge distributions that the distributions obtained by our method can be used to easily determine the relative variation of particle charging states, although the proportion of particles with a small charge number was quantitatively underestimated. The charge distributions of the atmospheric particles observed from April 2017 to February 2018 were different from the generally accepted stationary charge distribution. Moreover, the observed distributions changed significantly throughout the year. This variation was found to correlate with seasonal variations in temperature, relative humidity, volumetric humidity, and air mass trajectories. Present result suggests that the seasonal variation of the charging state is possibly due to the seasonal variation of the atmospheric ion number concentrations. Thus, it is important to consider the variation in the charging state of atmospheric particles due to dynamic changes of atmospheric conditions, as the charging state can dramatically influence the deposition of particles in the lungs.

The performance of aerosol classification schemes based on intensive optical parameters and applied to mixed particle populations monitored at the surface has been investigated to test the ability of optical parameters to identify different types of particles/particle mixtures and explore their complex features. The results show that the combination of two intensive optical parameters does not allow for the unique identification of different particle types. The classification scheme based on the Absorption Angstrom Exponent (AAE) as a function of the Scattering Angstrom Exponent (SAE) and color-coded by the Single Scattering Albedo difference (dSSA) is a good graphical framework to discriminate between different types of particle/particle mixtures. This aerosol classification scheme has been applied to study the optical properties of heterogeneous PM2.5 particles that were monitored at a coastal site of the Central Mediterranean and were significantly affected by both natural and anthropogenic sources also because of long-range transport from surrounding countries. The calculated AAE, SAE, and dSSA hourly means smoothly and continuously vary within their respective range (0.6-3.4, -0.7-3.0, and -0.33-0.52, respectively) because of the different mixing degree of different types of particles. Consequently, the main features of the particle populations depend on the range of the AAE, SAE, and dSSA values. Eight different clusters have been selected within the used graphical framework to identify four key particle populations (dust, marine, OC-dominated, and BC-dominated particles) and four particle mixtures dominated by key aerosol populations. In addition, their main features have been characterized. Particle mixtures consisting of large and low-absorbing particles (LLAP), small and high-absorbing particles (SHAP), dominated by dust, and large organic particles have been characterized. Marine, LLAP, and mixed dust clusters with a SAE value below 1 are responsible for aerosol scattering coefficients (sigma(s); at 470 nm) below 100 Mm(-1). Conversely, SHAP, BC-dominated, and OC-based mixtures are responsible for the highest sigma(s) values and represent dominant particles species.

New particle formation (NPF) events are important phenomena that generate nanoparticles and even fine particles via gas-to-particle conversion. These events have clear effects on aerosol loading, atmospheric chemistry and global climate. Long-term field measurements were used to characterize aerosol size distributions and to examine the role of atmospheric volatile organic compounds (VOCs) in NPF events in the urban environment of Shanghai. Aitken and accumulation particles are dominant and account for 85–95% of the total particles, whereas coarse particles are negligible. Particles in the four size-models show the same seasonality: highest in winter and lowest in autumn. The mean particle size distributions display different patterns of diurnal fluctuation, including bimodal in spring and winter, tri-modal in autumn, and “banana” shaped in summer due to highly frequent NPF events. The geometric mean diameter (GMD) is often 20–30 nm or 40–60 nm. Overall, NPF events occur on 89 days out of 335 measurement days (26.5%), and the newly formed particles have a mean growth rate of 6.28 nm h−1. Two typical anthropogenic aromatics, benzene and toluene, from traffic emissions closely match the occurrence of NPF events and have a weakly positive correlation with the nucleation particle number concentrations. The enhanced VOCs as precursors of organic vapors may contribute to the growth process of NPF events to some extent (e.g., growth rate) so that newly formed particles can grow into a detectable size.

This study was undertaken to investigate the spatial and temporal variation of sixteen priority Polycyclic Aromatic Hydrocarbons (PAHs) as per the classification of the United States Environmental Protection Agency (US EPA); bound to size-fractionated particles along with their sources and probabilistic risks in urban environments of Delhi-National Capital Region (NCR) of India, where quantification of PAHs was carried out through Gas Chromatography-Mass Spectrometry (GC-MS) for the samples collected during the period 2015–16. PAHs were observed to be highly concentrated in the smaller size ranges of particles throughout the analyses. Benzo[a]pyrene (12%) contributed the highest mean concentration, whereas Acenaphthene (2%) contributed least among the PAHs in size fractionated particles. Relative abundances of PAHs revealed that higher amount were associated with fine particles ( 2.5 μm) among the priority PAHs. Winter registered considerably maximum concentration of PAHs, whereas it was minimum during the rainy season. Spatial distribution of PAHs was interpolated by applying the spatial analyst extension Arc Geographic Information System (GIS) software (version 10.1). Molecular Diagnostic Ratio (MDR) and Principal Component Analysis (PCA) were performed for source apportionment of PAHs; where pyrogenic and petrogenic emissions were found to be the major contributors in the monitored sites. Incremental Lifetime Cancer Risks (ILCR; in terms of inhalation exposure) and Benzo[a]pyrene equivalent concentrations were investigated for toxicity assessment of PAHs. The priority PAHs having inhalation unit risk [(μg/m3)−1] were used for the investigation of ILCR associated with children and adults, where Benzo[a]pyrene possessed the maximum ILCR of all the PAHs.

The objective of this study is to characterise urban refractory black carbon (rBC) mixing state relative to hygroscopic growth factor (HGF) of size selective aerosols to better constrain the aerosol indirect effect. The Aitken mode range (≤100 nm) is dominated by particles that have relatively low hygroscopicity and comprised freshly emitted hydrophobic rBC, however, our observations suggest that BC mixing states in Aitken range (down to 70 nm) still govern the hygroscopic properties. Conversely, the accumulation mode range (>100 nm) dominated by particles that have relatively high hygroscopicity consisted of oxidized organic compounds and inorganic salts. Single particle soot photometer (SP2) measurement further revealed that particles at lower size are mostly incandescent type dominated by refractory component whereas higher size particles are mostly scattering type dominated by nonrefractory component. The lower hygroscopicity parameter (κ) (0.26 ± 0.08) obtained for Aitken mode particles suggests that they may contain levoglucosan and levoglucosan-OH oxidation products, and are possibly from biomass burning sources whereas accumulation range particles with higher κ value (0.39 ± 0.03) have ammonium sulfate, ammonium bisulfate and malonic acid in their composition and their possible source would be secondary in origin. These findings are important because for the first time, BC mixing state and the impact of size selective rBC on HGF are determined directly over an urban region which have implications to precipitation.

Though sulfuric acid and ammonia/alkyl amines are recognized as main contributors to new particle formation (NPF), models and observations have indicated that other organic species may be involved. In this study we introduced a suitable flow tube system to investigate the effect of formaldehyde (CH2O) on NPF from sulfuric acid and water at 297 K. Our results showed that nucleation rates are slightly enhanced when adding CH2O of 0.31–2.40 ppbv (in the range of atmospheric CH2O peak concentration) to stable sulfuric acid and water system at relative humidity (RH) of 30%, i.e., a rise of the particle number only by a factor of about 2, which is small in comparison to the millionfold increase caused by methylamine in similar conditions. And the promoting effect was weak under different RH. Cluster growth flux at experimental conditions, obtained from quantum chemistry-based cluster evaporation rate constants applied in a cluster population dynamics model, showed H2SO4-CH2O-based clusters are hard to grow. Therefore, the effect of CH2O on NPF via directly involving in the nucleation can be eliminated. In addition, the derived information may provide new insight into the impact of aldehydes on NPF.

Sea spray aerosol particle is a dominating part of the global aerosol mass load of natural origin. Thus, it strongly influences the atmospheric radiation balance and cloud properties especially over the oceans. Uncertainties of the estimated climate impacts by this aerosol type are partly caused by the uncertainties in the particle size dependent emission fluxes of sea spray aerosol particle. We present simulations with a regional aerosol transport model system in two domains, for three months and compared the model results to measurements at four stations using various sea spray aerosol particle source source functions. Despite these limitations we found the results using different source functions are within the range of most model uncertainties. Especially the model's ability to produce realistic wind speeds is crucial. Furthermore, the model results are more affected by a function correcting the emission flux for the effect of the sea surface temperature than by the use of different source functions.

In coastal regions and ocean areas, methanesulfonic acid (MSA; CH3SO3H) is present in considerable concentrations in the gas-phase and aerosols. It has been shown that MSA could contribute to growth and possibly form initial molecular cluster, which may lead to aerosol formation. However, quantitative concentrations and thermodynamic properties of MSA and sulfuric acid (SA; H2SO4) in the presence of water (W; H2O) remain largely uncertain. In this study, flow tube reactor was used to investigate the effects of each reactant on new particle formation (NPF) in a multi-component system consisting of MSA, SA, and W. Particles were measured for different combinations of reactants. It showed that a different order for reactant addition led to different experimental results, where the added MSA vapor to the SA-W binary system presented an obvious bimodal structure, for ternary system with SA added to the MSA-W, the similar bimodal phenomenon was not observed. The composition of clusters in the air flow was further analyzed by the commercial Atmospheric Pressure Interface Time-of-Flight Mass Spectrometer (APi-TOF-MS, Tofwerk AG), which is equipped with a homemade chemical ionization (CI) source, mass peaks corresponding to clusters that contain smaller MSA or SA molecules were clearly observed, indicating that these clusters are exist and stable. In addition, quantum chemistry calculation-based evaporation rate values were applied in a cluster dynamics model to yield formation rates of 2.6 × 102 cm−3 s−1 and cluster concentrations under different simulation conditions. This study could provide some insight into how acids interact in the atmosphere.

Source apportionment studies have been performed on online receptor datasets in recent years (called online source apportionment), including mass spectra and online chemical dataset. Single particle aerosol mass spectrometry (SPAMS), an important online technique, has the ability to analyze mass spectrum (MS) and particular size information of a single particle in real time. Clustering methods have been widely applied to MS dataset to investigate the sources of particles, although the receptor models are the common tools to probe the particle sources based on the receptor dataset. This work developed a new method (SPAMS-RM) that employed the receptor model (RM) on an MS dataset from SPAMS to identify particle sources. Particles were measured by SPAMS from July 14 to August 15, 2015, at an urban site in Tianjin, China. Multilinear Engine-2 (ME2) and adaptive resonance theory-based neural networks-2a (ART-2a) were separately used to analyze the single particle MS dataset. This work also evaluated the performance of SPAMS-RM method. Concentrations of chemical components of PM2.5 (particulate matter with an aerodynamic diameter of less than 2.5 μm) and gaseous pollutants were measured by independent online instruments (1 h resolution). Source apportionment was separately conducted using two receptor models, Positive Matrix Factorization (PMF) and ME2, based on the 1 h resolution chemical dataset. This method was called online chemical source apportionment (OCSA-RM). ART-2a obtained 19 clusters that merged into five major classes: carbon species, rich-K, sea salt, crustal dust, and industrial metals. SPAMS-RM identified eight sources by interpreting the MS characteristic of factors and investigating the relationship of the temporal trends of factor contributions, chemical species, gaseous pollutants, and particle clusters. OCSA-ME2 and OCSA-PMF both identified seven factors. Source apportionment results between SPAMS-RM and OCSA-ME2/PMF were compared. Each method identified coal combustion, biomass burning, sea salt, nitrate source, sulfate source, vehicle emission, and crustal dust. The SPAMS-RM results showed that nitrate source was the most significant contributor (34%) to the PM followed by sulfate source (17%), coal combustion (14%), crustal dust (11%), vehicle emission (10%), biomass burning-OCEC (7%), and industrial activities & sea salt (4%). Some differences between SPAMS-RM and OCSA-ME2/PMF results existed and might be due to chemical analysis methods and sampling methods. ME2 was used for the first time to identify the PM sources based on the MS dataset from SPAMS and demonstrated its capability when coupled with MS dataset from SPAMS to apportion the source of PM.

Levoglucosan has been extensively used as a molecular marker of biomass burning in source-apportionment studies over the last few decades. However, recent studies suggest that the atmospheric lifetime of levoglucosan may be in the order of only 1–2 days under summertime conditions relevant to prescribed/wildfires. Implications of levoglucosan reactivity to wintertime conditions, however, remain uncertain despite significant contributions of domestic wood combustion to wintertime air quality. This study presents smog chamber experiments to investigate levoglucosan decay during photo-oxidation of wood smoke over a temperature range between −8 and 10 °C. Significant decay in particle wall-loss corrected levoglucosan is only observed around 10 °C in these experiments. Theoretical analysis shows that the apparent chemical lifetime of levoglucosan increases at lower temperatures as well as at higher organic aerosol mass concentrations as a result of smaller vapor fractions. The chemical lifetime of a molecular marker is commonly interpreted by a relationship between relative decay in particle wall-loss corrected marker concentrations versus integrated OH exposure. However, this relationship strongly depends on vapor wall-loss rates in addition to temperature, organic aerosol concentrations, and OH concentrations. Therefore, inferred lifetimes from a small set of experiments from a single chamber cannot easily be generalized for the full range of atmospheric smoke conditions.

Oxalic acid is the most abundant dicarboxylic acid in the atmosphere, but the processes involved in its formation in ambient aerosols are still uncertainty. We used single particle aerosol mass spectrometer to investigate the sources and formation mechanisms of oxalic acid-containing (C2) particles in ambient aerosols in Chengdu during summer and winter seasons. C2 particles accounted for 2.9 and 0.7% of the total amount of fine particles detected in summer and winter, respectively. The C2 particles in each season were classified as nine different types of particle with significant seasonal differences in their contribution to total C2 particles. The oxalic acid-sulfate (C2-SO4) particles and particles related to biomass burning (i.e., oxalic acid-organic nitrogen (C2-CN) and oxalic acid-elemental carbon (C2-EC)) represented 78% of the total C2 particles in summer, whereas the contributions of oxalic acid-dust (C2-D), oxalic acid-sulfate and nitrate (C2-SN), and oxalic acid-nitrate (C2-NO3) particles clearly increased in winter. Although the peak diameter of the average size distribution of total C2 particles was larger in winter than in summer, there was no significant seasonal difference in the number fraction of the size-resolved particles for each type of particle. The peak concentration of total C2 particle in summer occurred in the afternoon, but there was no obvious diurnal variation in winter. We concluded that local photochemical oxidation in the daytime favored the production of C2 particles in summer, whereas in-cloud processing with subsequent long-distance transport had an important effect on C2 particles in winter. The potential source contribution function (PSCF) analysis indicated that local sources from the eastern, southeastern, and southern regions of Sichuan Province dominated the C2 particles in summer, whereas the contribution from the long-distance transport of aerosols originating outside Sichuan Province was significantly enhanced in winter. These findings will help us to understand the formation of secondary organic aerosols in the atmosphere over the Sichuan Basin.

The size distribution of a particle population has proven to be of great value in source apportionment studies. Previous studies have reported that particle size distributions in ambient urban air vary with location and time, indicating that the ambient particles are affected by known sources. However, the size distributions of individual chemical species emitted from primary sources have received relatively little attention. This study presents a preliminary real-world investigation of the size distributions of particles emissions from coal-fired power plants, residential coal combustion, biomass burning, vehicles, soil dust and steelworks based on a high size-resolution measurement using an Electrical Low Pressure Impactor. The size profiles of individual chemical elements are found to have a high degree of source specificity, which assists source classification. We subsequently employed a chemical mass balance approach termed size-resolved CMB (SR-CMB), which is based on the use of both physical and chemical information on the high size-resolution measurements of particulate matter. By applying SR-CMB on the measured ambient data, source contributions to ambient particles were successfully obtained when copper (Cu) was chosen as the fitting species. The approach described in this paper enhances the capability of the CMB model and provides a useful tool to validate results of traditional receptor models when a high size-resolution measurement is available. This effort also highlights that the size profiles of sources is of potential concern in the situations when the chemically collinear sources exist.

Formation of haze is a phenomenon dependent on the relative atmospheric humidity and concentration of aerosol particles. The physical and chemical reactions on particle surfaces would lead to variations in particle sizes. This paper focuses on the physical behaviour of aerosol particles under the influence of atmospheric humidity, which produces liquid bridging forces and electrostatic interactions among particles. By water absorption experiment, a correlation between relative humidity (RH) and water content on particles was obtained. Through theoretical derivation, a relationship between the relative humidity and humidity ratio was established for calculating liquid bridging forces. The findings from experiments on atmospheric particles charging, showed most aerosols were negatively or positively charged and the average charges on these particles was more than one. An extended soft-sphere discrete element method (DEM) was used to simulate the evolution of aerosol particles, encapsulated in water vapour by considering liquid bridging forces, electrostatic interactions and Brownian forces. Results suggest that the agglomeration rate of particles would increase with a rise in the atmospheric humidity due to the increased liquid bridging forces that enhance the agglomeration velocity. The higher humidity would enhance the ionization on particle surfaces, which could affect electrostatic interactions. This paper provides an insight of a mechanism for formation of haze in atmosphere.

© 2018 Elsevier Ltd Compared to the space-borne estimation of PM 2.5 (particulate matter with aerodynamic diameter ≤2.5 μm), the investigation of PM 1 (≤1 μm) remains less intensive and thus unclear. Here we estimated four years (2014–2017) of ground-level PM 1 concentrations from MODIS aerosol optical depth (AOD) in attempt to gain a better understanding of much finer particles. The Yangtze River Delta (YRD) region, with a relatively dense ground-based PM 1 station network, was selected as the study area. The geographically and temporally weighted regression (GTWR) model simultaneously accounting for spatial and temporal variability existing within various predictors was constructed. Validation of satellite-estimated PM 1 against ground-measured PM 1 yields a high consistence, significant improvement over previous work (R 2 = 0.74 VS 0.59, RMSE = 13.02 μg/m 3 VS 22.5 μg/m 3 ). This suggests the PM 1 estimates from GTWR model are reliable and robust enough to obtain large-scale fine particle contents. The population exposure of air pollution in the YRD region, therefore, has been analyzed by calculating population-weighted mean PM 1 concentrations, which reaches as high as 37.22 μg/m 3 . Further analysis indicates that near half the people live in locations with high-level PM 1 concentration (>35 μg/m 3 ), which has profounding implication for improving our understanding of human exposure to fine aerosol particles.

Aerosols affect the Earth's radiation budget by interacting with the incoming solar radiation. The physico-chemical properties, particularly morphological parameters (Aspect Ratio, AR and Circulatory Factor, CIR) and composition at individual particle level are important inputs to the optical model for assessing the optical sensitivity towards said properties. The observation of these properties is limited over Antarctica which has been studied in detail in the present work. The PM5 particles (particulate matter with aerodynamic diameter less than 5 μm) over Antarctica were collected at Indian Antarctic station, Maitri (70.77°S, 11.73°E) from Dec 2013–Feb 2014. The individual particle analysis revealed that particles were mainly composed of Si, Fe, Al, Ca and Mg. Most of the particles were observed in layered, flattened, aggregated and glass-like shapes. The frequency distributions of the morphological parameters, AR and CIR were observed to be bimodal with respective mode peaks 1.3 and 1.9 for AR; 0.4 and 0.7 for CIR. The spectral refractive indices of individual particles were estimated. The imaginary part of the refractive indices was observed to be maximum for chromium (Cr) and iron (Fe) rich particle and nearly negligible for aluminum (Al) rich particle. At 0.58 μm wavelength, the difference in SSA with respect to Al rich particle was found to be maximum for Ca rich particles (i.e. 43%) followed with Cr and Fe rich particle (i.e. 42.08%) and Cr rich particle (i.e. 39.32%).

A total number of 109 new particle formation events identified in the ion-mobility spectra measured with a Neutral Cluster and Air Ion Spectrometer in the mobility range of 3.16–0.00133 cm2 V−1s−1 (Diameter* range 0.36–47.1 nm) at a tropical site at Pune, (18.53 °N, 73.85 °E, 573 m amsl) India from March 08, 2010–December 31, 2012 are classified based on their shape characteristics under four categories. Most of these events occurred in the morning hours of the pre-monsoon season during the hottest months (April and May) of the year. The meteorological conditions and the changes in ion characteristics associated with some typical events are examined. Average ion-mobility spectrum for the event days shows a minimum in the negative big cluster ion (diameter, 0.85–1.6 nm) concentration and two maxima in the positive intermediate (diameter, 1.6–7.4 nm) and large ion (diameter, 7.4–47.1 nm) concentrations as compared to the average spectrum for all days. Analysis of 7-days airmass back trajectories shows that since the only source of big cluster ions is through the growth of small cluster ions (diameter, 0.36–0.85 nm) the growth of small to big cluster ions is faster when the airmass approaches our site from the land. Further, the concentrations of positive intermediate and light large (diameter, 7.4–22 nm) ions is more when the airmass approaches from the Arabian Sea.

Methanesulfonic acid (MSA) is believed to play an important role in the formation and growth of atmospheric organic aerosols and could facilitate the binary nucleation of sulfuric acid (SA)–water (W). However, understanding of larger clusters formed by gas-phase MSA with atmospheric nucleation precursors from microscopic aspect is lacking. In this work, to study the microscopic mechanism of the ternary nucleation, the structural characteristics and thermodynamics of MSA clusters with SA in the presence of up to six W molecules have been investigated. It was found that MSA forms relatively stable clusters with SA and W molecules and that acid dissociation plays an important role. The analysis of the atmospheric relevance indicates that the heterodimer MSA–SA and monohydrated cluster MSA–SA–W1 show an obvious relative concentration in the atmosphere, and thus, these species likely participate in new particle formation (NPF). However, with an increasing number of W molecules, the concentration of clusters gradually decreases. Additionally, the minimum energy isomer of MSA–SA–W4 is predicted to possess a relatively stable configuration under the employed temperature dependence analysis, and evaporation rate analysis. The detailed non-covalent interactions of MSA-SA-Wn, n = 3–6 cluster have been thoroughly studied for the first time.

Air quality in the city of Innsbruck, Austria, is affected by transalpine traffic and mountainous terrain, which is characterized by a pronounced mountain – valley wind system often favouring high pollution levels. To contribute to a better understanding of urban air pollution mechanisms in an Alpine valley, eddy covariance (EC) measurements with a condensation particle counter (CPC) were performed at an urban site in Innsbruck in the framework of the Innsbruck Air Quality Study (INNAQS). Emission fluxes of 10.6⋅107 m−2 s−1 (median) were observed during daytime and up-valley flow, whereas fluxes during reversal periods of the valley wind system were more variable and partly negative. Sporadic gust-like motions of vertical wind and concurrently measured large changes in particle number concentration (termed particle gusts) significantly biased total particle fluxes, reflecting, however, rather local fluxes at the measurement height. The particle gust events were identified by applying the median absolute deviation (MAD) method to particle fluxes. The particle flux was reconstructed by means of a continuous wavelet transform (CWT) to confirm the validity of the EC calculations during particle gusts. Their origin could not clearly be identified, but they indicate the presence of poorly mixed air parcels which are strongly enriched with particles. Due to the episodic yet large contribution to particle fluxes in Innsbruck, the potential impact of particle gusts on turbulent particle exchange should also be evaluated at other urban and non-urban sites.

Aerosol fluxes were measured by eddy-correlation for 8 weeks of the summer and fall of 2011 above a temperate broadleaf forest in central Ontario, Canada. These size-resolved measurements apply to particles with optical diameters between 50 and 500 nm and are the first ones reported above a temperate deciduous forest. The particle spectrometer was located on top of the flux tower in order to reduce signal dampening in the tube and thus maximize measurement efficiency. The 8-week data set extends into autumn, capturing leaf senescence and loss, offering a rare opportunity to investigate the influence of leaf area index on particle transfer. A distinct pattern of emission and deposition that depends on the particle size is highlighted: while the smallest particles (dp 100 nm) are preferentially deposited (62% of the time). For the size bins with detection efficiency above 50% (68–292 nm), the median transfer velocity for each bin varies between +1.34 and −2.69 mm s−1 and is equal to −0.21 mm s−1 for the total particle count. The occurrence of the upward fluxes shows a marked diurnal pattern. Possible explanations for these upward fluxes are proposed. The measurements, and their comparison with an existing model, highlight some of the key drivers of the particle transfer onto a broadleaf forest: particle size, friction velocity, leaf area index and atmospheric stability.

Moisture plays a crucial role in the heterogeneous formation of sulfur compounds on mineral dust particles. The heterogeneous uptake of SO2 under various humidity conditions, however, is not well explained. In this study, heterogeneous reaction of SO2 on hematite particles are investigated using an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The interaction of SO2 with H2O is divided into the initial moisture absorption stage and the subsequent heterogeneous oxidation stage, indicating physical adsorption and chemical conversion of SO2, respectively. Uptake coefficients were estimated by Brunauer-Emmett-Teller (BET) surface area and geometric surface area. For unreacted (fresh) particles, the coefficients peak at 33% RH and then decline with increasing RH in both stages, implying the competition between SO2 and large amount of adsorbed H2O besides the promoting effect of water. For hematite after in-situ exposure to SO2 (sulfated particles), the coefficients increase as a function of RH in moisture absorption stage, indicating SO2 adsorption with particle hygroscopic growth. Nevertheless, the coefficients exhibit similar variation with that for fresh particles in heterogeneous oxidation stage, highlighting the competition effect after H2O accumulation. Generally, H2O plays both positive and negative roles in the adsorption of SO2. Reaction on sulfated hematite is significantly influenced by previously formed sulfate compounds with low hygroscopicity. Moreover, sulfate products may influence particle acidity after H2O introduction, and further result in diverse existence forms of S(IV) species. The extremely great uptake capacity of sulfated particles in moisture absorption stage may offer opportunities to explain the severe haze in high RH.

Ultrafine particles with diameters less than 100 nm suspended in the air are a topic of interest in air quality and climate sciences. Sub-10 nm particles are of additional interest due to their health effects and contribution to particle growth processes. Ambient measurements were carried out at North Carolina State University in Raleigh, NC between April to June 2019 and November 2019 to May 2020 to investigate the temporal variability of size distribution and number concentration of ultrafine particles. A mobile lab was deployed between March and May 2020 to characterize the spatial distribution of sub-10 nm particle number concentration. New particle formation and growth events were observed regularly. Also observed were direct emissions of sub-10 nm particles. Analysis against meteorological variables, gas-phase species, and particle concentrations show that the sub-10nm particles dominated number concentration during periods of low planetary boundary layer height, low solar radiation, and northeast winds. The spatial patterns observed during mobile deployments suggest that multiple temporally stable and spatially confined point sources of sub-10 nm particles are present within the city. These sources likely include the campus utility plants and the Raleigh-Durham International Airport. Additionally, the timing of data collection allowed for investigation of variations in the urban aerosol number size distribution due to reduced economic activity during the COVID-19 pandemic., Highlights • A monthly average of 8 new particle formation events contribute to the ultrafine particle number concentration. • Multiple distinct anthropogenic sources of sub-10 nm sized particles are identified. • A slight reduction in number concentration was observed during the the COVID-19 pandemic.

Aerosol microphysical properties, scattering and absorption characteristics, and in particular, the vertical distributions of these parameters over the eastern Loess Plateau, were analyzed based on aircraft measurements made in 2020 during a summertime aircraft campaign in Shanxi, China. Data from six flights were analyzed. Statistical characteristics and vertical distributions of aerosol concentration, particle size, optical properties, including aerosol scattering coefficient (σsp), backscattering ratio (βsc), Angstrom exponent (α), single-scattering albedo ( S S A ), partially-integrated aerosol optical depth (PAOD), and black carbon concentration (BCc), were obtained and discussed. Mean values of aerosol particle number concentration (Na), particle volume concentration (Va), mass concentration (Ma), surface concentration (Sa), and particle effective diameter (EDa) were 854.92 cm−3, 13.37 μm3 cm−3, 20.06 μg/m3, 170.08 μm3 cm−3, and 0.47 μm, respectively. Mean values of BCc, σsp (450, 525, 635 nm), βsp (525 nm), α(635/450), and SSA were 1791.66 ng m−3, 82.37 Mm−1 at 450 nm, 102.57 Mm−1 at 525 nm, 126.60 Mm−1 at 635 nm, 0.23, 1.47, and 0.92, respectively. Compared with values obtained in 2013, Na decreased by 60% and Ma decreased by 45%, but the scattering coefficients increased in different degrees. In the vertical direction, aerosol concentrations were higher at lower altitudes, decreasing with height. Vertical profiles of σsp, βsp, α(635/450), and BCc measured during the six flights were examined. Two peaks in Na were identified near the top of the boundary layer and between 2000 and 2200 m. Fine particles with EDa smaller than 0.8 μm are dominant in the boundary layer and coarse aerosols existed aloft. Aerosol scattering properties and BCc in the lowest layer of the atmosphere contributed the most to the total aerosol radiative forcing. SSA values were greater than 0.9 below 2500 m, with lower values at higher levels of the atmosphere. On lightly foggy days, SSA values were greater than 0.9, and aerosols played a cooling role in the atmosphere. On hazy days, lower-level SSA values were generally greater than 0.85, with aerosols likely having a warming effect on the atmosphere. 48-hour backward trajectories of air masses during the observation days showed that the majority of aerosol particles in the lower atmosphere originated from local or regional pollution emissions, contributing the most to the total aerosol loading and leading to high values of aerosol concentration and radiative forcing.

Levels of eleven organophosphate esters (OPEs) were measured in particle phase atmospheric samples collected at Bohai Sea and northern Yellow Sea in China. The concentration of ∑11OPEs in atmospheric particles ranged from 426 to 3933 pg/m3, with the mean concentration of 1412 pg/m3. Tris(1-chloro-2-propyl) phosphate (TCPP) and triphenyl-phosphine oxide (TPPO) were the most abundant OPE congeners measured, and the individual concentrations of trimethyl phosphate (TMP), tri-iso-butyl phosphate (TiBP), tri-n-butyl phosphate (TnBP), tris(1,3-dichloro-2-propyl) phosphate (TDCP), triphenyl phosphate (TPhP), 2-ethylhexyl diphenyl phosphate (EHDPP), TPPO and tri-m-cresyl phosphate (TMTP) in atmospheric particles above the Bohai Sea were higher than those above the northern Yellow Sea. The estimated atmospheric dry deposition fluxes ranged from 202 to 1869 ng/m2/day. Up to 18.3 ± 12.5 ton/year of OPEs can be loaded to the Bohai Sea.

Particle formation in point source plumes is a typical sub-grid process not explicitly resolved in chemical transport models, and is an important contributor to atmospheric aerosols. The sub-grid particle formation (SGPF) is closely associated with the concentration of hydroxyl radical and condensation sinks in the plume, thus it has diurnal, seasonal and spatial variations. The impacts of SGPF in point source plumes on both aerosol mass and number concentrations were first investigated in China by a newly developed global nested chemical transport model with a SGPF parameterization scheme. Although a mean oxidation fraction of 2.5% sulfur dioxide for parameterizing the SGPF is suggested, the oxidation fraction and the particles formed in point source plumes have clear spatiotemporal variations based on the results of the SGPF scheme. The SGPF can enhance the annual mean concentration of sulfate by more than 1 μg m−3 (10–25%) over high emission areas (HEAs) in central-eastern China (CEC). In terms of particle number concentration, the SGPF contributes much more to nucleation mode particles with increasing number concentration, by 25–50% in HEAs, 10–25% in CEC, and 1–5% in northwestern China (NWC) compared with lower values (within ±5%) for the accumulation mode. This study reveals the significant impacts of SGPF over China and its strong dependence on meteorological and environmental factors. Physically-based SGPF scheme should be incorporated when studying the regional effects of point source plumes on air quality and climate.

Marine aerosols have significant impacts on the global radiation balance and climate. New particle formation (NPF) is an essential source of aerosol formation. Sulfur-containing acids (sulfuric acid (SA), methanesulfonic acid (MSA), and methanesulfinic acid (MSIA)) oxidized from ocean-emitted dimethyl sulfide (DMS), have been identified as nucleation precursors in marine NPF. Given their homology, these sulfur species are likely to contribute jointly to the NPF. However, the joint effects of such sulfur acids on NPF and the nucleating mechanism remain unknown. Hence, the first quaternary SA-MSA-MSIA-DMA nucleation system was systematically investigated under different conditions using density functional theory (DFT) combined and Atmospheric Cluster Dynamic Code (ACDC). The results indicate that MSA and MSIA can synergistically enhance the formation rates of SA-dimethylamine (DMA) clusters, especially in regions with low temperatures, sparse SA and DMA. In the mid-latitude oceans, MSA and MSIA can jointly promote nucleation by forming SA-MSA-DMA and SA-MSIA-DMA clusters like ‘division of cooperation’. While in the cold polar regions, MSA and MSIA can synergistically enhance clustering via forming stable MSA-MSIA-based clusters like ‘hand in hand’. The proposed quaternary SA-MSA-MSIA-DMA mechanism manifests itself more effectively in the nucleation process, and such a multi-component nucleation model may help us to understand the frequent marine NPF more comprehensively.

During normal operations, buildings can protect their occupants from outdoor airborne particle hazards of all types, including airborne pollutants. A long-term international research effort has advanced our knowledge of building protection physics. Recently we have developed an operationally efficient, regional-scale methodology - Regional Shelter Analysis - to account for both building protection effects and the typical distribution of people in and among buildings. To provide input to this capability, we estimate here the degree of protection afforded by the currently existing US building stock. We first assemble and summarize the published literature relevant to indoor particle losses including (a) deposition to indoor surfaces, (b) losses that occur when particles penetrate through the building envelope, and (c) heating, ventilation and air conditioning (HVAC) system filtration efficiencies as well as general building operating conditions. Building protection against inhaling particulate hazards varies strongly, by orders of magnitude, according to building use (occupancy), particle-size, and airborne particle loss rate. Protection increases modestly as particle size increases from 0.1 to 1 μm and significantly as particle size increases from 1 to 10 μm. Model results are placed in context with previously reported measurements. Suggestions for future work, including enhanced validation datasets are provided. Description of Supplemental Materials

Haze related air pollution has become one of major environmental concerns in some Asian countries. Sulfate is a main component of ambient particulate matter (PM) in the urban environment during haze episodes. Among the pollutants, sulfur dioxide (SO2) is an important precursor of sulfate and new atmospheric particle formation. However, under different atmospheric conditions its underlying formation mechanisms are not clearly elucidated. In the current work, we collected ambient PM in two cities: Zurich (Switzerland) and Beijing (China). The PM morphology and the composition were investigated by scanning electron microscopy, energy dispersive X-Ray spectroscopy and Raman micro-spectroscopy. In addition, a series of lab controlled experiments were also performed to study the SO2 reaction with CaCO3 aerosol. We found different types of CaSO4·2H2O crystals in the Chinese urban samples, with clearly different compositions than those from Zurich. The experimental data showed that the relative humidity played a significant role on the new CaSO4·2H2O crystal formation including its size, morphology and composition. Relative humidity (RH) above 80% can significantly promote SO2 oxidation on the CaCO3 particles and form the CaSO4·2H2O crystals. In contrast, at relative humidity below 40%, only few CaCO3 particles can be converted to CaSO4 particles. The results of this study facilitate the understanding of secondary inorganic aerosol formation by the reaction of CaCO3 particles with SO2 with different RHs in different city environments, and provide useful information for air pollution control.

Recently, the correlation between the new particle formation (NPF) events and oxygenated organic molecules (OMs) was observed frequently in forest ambient. However, the understanding of OMs-driven NPF mechanism at the molecular level remains ambiguous. The participation of eight organic compounds (Orgs) together with sulfuric acid (SA) respectively in the initial steps of NPF was investigated by the quantum-chemical calculation and Atmospheric Cluster Dynamics Code (ACDC). Thermodynamic and structural analysis prove that most of (Org)x(SA)y (0 = x ≤ 2; 0 = y ≤ 2) clusters possess stable H-bonds, but other interactions, such as steric hindrance, should not be ignored when investigating their stabilities and reaction properties. Furthermore, the cluster formation rates of eight Org-SA systems are calculated and found to be different at three levels: (1) systems involved 3-carboxyheptanoic acid (CHA) and phthalic acid (PTA) present high formation rates exceeding 10−3 cm3 s−1, which indicate their high nucleation abilities; (2) systems containing cis-3-caric acid (CRA), limonic acid (LMA) and 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) have medium formation rate values from 10−6 to 10−4 cm3 s−1; and (3) systems including cis-pinic acid (PNA), 2-methyltetrols (MT) and 2-methylglyceric acid (MGA) present low formation rates less than 10−8 cm3 s−1. Our comparison results of theoretical researches about eight Orgs and SA indicate that OMs are expected to make important contributions to NPF under real atmospheric conditions. Especially, CHA and PTA, the crucial oxidation product of monoterpene and aromatic respectively, represent considerably strong potential abilities to form the critical clusters unexpectedly, and more attention should be paid to their effects on NPF in the real environment.

Despite its profound influence on air quality, the aerosol acidity, quantifiable by aerosol pH is poorly characterized in South Korea where high concentrations of fine particles have become a serious environmental issue. In this study, we estimated the pH values of PM2.5 using observations of inorganic species and precursor gases concentrations, ambient temperature and relative humidity (RH), measured at the Olympic Park in Seoul during the KORUS-AQ campaign (10 May to June 19, 2016). For the aerosol pH calculation, the ISORROPIA and E-AIM thermodynamic equilibrium models in forward mode were used, in which we found the phase state assumption, either stable (solid + liquid) or metastable (liquid only) had no significant impact on pH predictions. As reported previously, the unrealistic pH prediction of ∼7.6 by ISORROPIA, which largely misrepresents ammonia-rich aerosol contents in the Seoul atmosphere was mainly due to coding errors in the standard ISORROPIA model (i.e., forward mode with stable state assumption). Using the revised ISORROPIA, pH predictions obtained with stable assumption approached those obtained with the metastable state assumption. Following such amendment, fine particle samples were predicted to be acidic with pH values ranging from 1.5 to 4.0 as determined by both ISORROPIA and E-AIM calculations. These pH values were higher than those reported in the United States and Europe and lower than those reported in northern China. A comparison of ISORROPIA and E-AIM models revealed that the pH values obtained using ISORROPIA were consistently but only ∼0.4 pH unit higher than those obtained using E-AIM, demonstrating the precision and consistent utility of thermodynamic equilibrium model in the quantification of PM2.5 pH in Seoul.

Free amino acids (FAAs) are particularly interesting because they play an important role in the atmosphere, but their origins are not well understood. This study measured the concentrations of FAAs and water-soluble ions as well as δ15N values of Glycine (Gly) in total suspended particle (TSP) samples collected at Nanchang in 2017. The correlation of total FAAs concentrations with meteorological conditions and atmospheric oxidants showed that secondary formation processes could be an important contribution sources for FAAs in the atmosphere. Moreover, the concentrations of FAAs in aerosols may be affected by the wind directions and the regions where air mass passed. The correlations of FAAs with water-soluble ions and PMF analysis indicated that the concentration of FAAs in Nanchang aerosols was influenced by agricultural activities and dust sources, mixture of natural origins and biomass burning and mixture of secondary formation process and biomass burning. Interestingly, we also found that coal combustion and vehicle emission are not the sources for atmospheric FAAs. Based on δ15N values of free Gly, a Bayesian model was performed to obtain the individual fractional contributions of free Gly from major sources (natural and biomass burning sources) to aerosol Gly. Subsequently, applying fractional contributions of free Gly from biomass burning obtained by Bayesian model to the analysis result of PMF, the overestimated of the contribution of secondary formation processes and natural sources to atmospheric FAAs concentration caused by biomass burning source could be excluded. Our findings suggest that combining δ15N values of free Gly and PMF analysis could provide further information on the sources of atmospheric FAAs.

Organosulfur compounds are being of increasing interest in the atmospheric environment and climate because of their profound impacts on the formation of secondary organic aerosol. However, their role in the initial step of new particle formation (NPF) is still unclear. Here, using Density Functional Theory (DFT) calculation combined with the Atmospheric Clusters Dynamic Code (ACDC) model, we study the enhancement effect of hydroxymethanesulfonic acid (HMSA) - one of the most important organosulfur compounds - on sulfuric acid (SA) - dimethylamine (DMA) molecular clustering and the underlying mechanism. The results show that HMSA can enhance cluster formation rates at room temperature with the enhancement strength ranging from zero to four orders of magnitude. The comparison of the enhancement effect between HMSA and MSA shows that the enhancement strength of HMSA could be up to 3.97 times stronger than that of MSA, indicating that HMSA may be a more potential stabilizer. Meanwhile, different from the “bridge” role of α-hydroxyl acids, HMSA acts as “stabilizer” directly participating in NPF. Both of its enhancement strength on cluster formation rate and the corresponding contribution to the growth pathway present a negative dependence on SA concentration. All those could, to some extent, help to explain the missing sources of NPF between field observation and currently cognition, as well as to assist us to better understand atmospheric organosulfur chemistry.

A framework to describe transport and deposition of ultrafine particles (UFP) within forests using large eddy simulation (LES) is presented. Comparison with measurements collected within and above a Scots pine stand in Southern Finland are used to explore the plausibility of the simulations. The numerical model is then employed to quantify the effects of canopy morphology (leaf area index and leaf area density), turbulence intensity, and particle size on the partitioning between upper canopy and subcanopy deposition and the overall deposition velocities. Results show a complex interplay between canopy morphology and turbulence, which is reflected on the particle flux profiles within the canopy. However, mean particle concentration profiles, total deposition, and deposition velocities at the canopy top are insensitive to the leaf area density profile but show dependence mostly on leaf area index, turbulence levels, and particle size. Finally, with the goal of understanding the sensitivity of the deposition velocity to all these parameters, an analytical model is developed that shows good agreement with LES results (within ± 20 % ) for all conditions simulated here.

Aerosol size distributions were measured using a scanning mobility particle sizer (SMPS), and also PM1 (particulate matter ≤ 1 μm in aerodynamic diameter) samples were collected in parallel at a representative site in New Delhi during spring in 2013 and 2014. Based on the temporal variation of particle count mean diameter (CMD), sampling periods are characterized as growth events and non-growth events. Particle size distribution measurements suggest that some consecutive nights experienced unique nighttime subsequent growth of particles, which sustained for a longer period. Average particle growth rate measured during growth events was 5.64 ± 3.03 nm h−1. Atmospheric trace gas concentrations and meteorological data show that these growth events (nighttime) are influenced by higher concentrations of gases, e.g., NO2 (56.5 ± 29.7 μg m−3), SO2 (9.34 ± 1.14 μg m−3) and RH (45.7 ± 9.5%) than those of non-growth events (daytime) (37.9 ± 18.6 μg m−3, 7.19 ± 2.08 μg m−3 and 37.7 ± 6.9%, respectively). Further, analysis of PM1 samples collected during the study period shows that the particulate water-soluble organic carbon (WSOC) (12.7 ± 4.1 μg m−3), NH4+ (9.4 ± 3.2 μg m−3), SO42− (2.03 ± 0.70 μg m−3), K+(1.06 ± 0.40 μg m−3), and NO2− + NO3− (0.59 ± 0.36 μg m−3) are the major contributors of particulate mass, wherein NH4+, SO42−, K+, NO2− + NO3− mass concentrations were higher during growth events. Correlation study shows that nighttime aerosol composition during growth (in sub-micron range) events are more enriched by inorganic species (i.e., NH4NO3, (NH4)2SO4 and H2SO4 vapors) as compared to organics (i.e., WSOC, does not show much difference in growth events and non events). Our results suggest that nighttime sulfate formation at the site is mostly mediated by high NO2 and NH3 at elevated RH. For the formation of sulfate and other inorganic species, a nighttime atmospheric chemistry is proposed, which is linked to particle growth. Growth events observed typically in nighttime have both biomass burning and anthropogenic influences as indicated by high concentrations of WSOC, K+ and black carbon in PM1 and carbon monoxide in gas phase.

An intensive measurement campaign was conducted at a rural site in Northwest China to investigate aerosol optical absorption properties, using the ground-based mobile facility of the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). The average mass concentration of PM2.5 was 103 ± 4 μg m−3 during the 20-day campaign in April 2014. Black carbon (BC) only accounted for ∼0.4% of the PM2.5 on average, with the mean concentration of 443 ± 12 ng m−3 measured using a single particle soot photometer (SP2). The aerosol absorption coefficient (σap) was 5.69 ± 0.01 Mm−1 on average, recorded by a multi-angle absorption photometer (MAAP) at the wavelength of 637 nm. It showed a linear relationship with BC mass concentration during non-dust periods, especially at their diurnal peaks of 07:00–09:00 a.m. (local standard time), deriving a bulk mass absorption efficiency (MAE) for BC of 8.5 ± 1.1 m2 g−1. The σap increased sharply during the dust storm, while the BC remained at a lower concentration than other moments, implying that the dust particles had a considerable contribution to light absorption. On average, dust particles accounted for 26.7% of the aerosol absorption and increased to 71.6% during the dust storm. The MAE of dust was calculated to be 0.014 ± 0.00028 m2 g−1, which was comparable to that measured in the downwind regions in East Asia. Based on the Mie theory for spherical particles, the refractive index (m) of natural mineral dust particles was estimated to be 1.50–0.0007i in Northwest China.

Particle number size distribution in a suburban Beijing was measured during the HOPE-J3A (Haze Observation Project Especially for Jing–Jin–Ji Area) field campaigns in 2015 from 18 June to 23 July (summer) and 2 to 25 December (winter). Average particle concentrations during the summer and winter campaigns were 9.6 ± 4.8 × 103cm−3 and 13.9 ± 8.3 × 103cm−3, respectively. Particle numbers were dominated by Aitken mode particles in both seasons. During the winter campaign, pollution events occurred every four to five days, each lasting for two to three days. In contrast, pollution events lasted for one to two days every six to seven days during the summer campaign. Aitken mode particles were 50% higher in the winter but new particle formation (NPF) events occurred more frequently in the summer. NPF events usually starts at around 10:00 LT (local time) in the summer but 12:00 LT in the winter. Aitken and accumulation mode particles accounted for 43.5% and 38.2% of all particles. The proportion of Aitken mode to total particles remained almost the same during summer, while it increased as haze intensified in winter. Particle number concentration was closely correlated with traffic and residents living activities and wind speed, with higher concentrations during rush hours, heating period and in the southerly wind. These results, when combined with trajectory cluster analysis, suggest that Aitken and accumulation mode particles were mainly from regional transport during the summer campaign, but from vehicle and coal-combustion emissions during the winter campaign.

Particle number size distributions are among the most important parameters in trying to understand the characteristics of particle population. Atmospheric particles were measured in an interaction of mixed environments in the Southeastern coastal city of Wollongong, Australia, during a comprehensive field campaign known as Measurements of Urban, Marine and Biogenic Air (MUMBA). MUMBA ran in summer season between 21st December 2012 and 15th February 2013. Particle number concentrations measured during this campaign were indicative of the interplay between marine environments and urban air which met the objective of this campaign. Particle number size distributions ranging from 14 nm to 660 nm in diameter, as measured by Scanning Mobility Particle Sizer (SMPS) in this study, were grouped using Principal Component Analysis. Based on strong component loadings (value ≥ 0.75), three different factors were identified (i) Small Factor (NS): 15 nm

The estimation of particle removal rates in closed atmospheric environments such as rooms or airplanes is of great interest because it is directly relevant to air quality and disease transmission. In this work we investigate experimentally and numerically the depletion of micron-sized particles inside a turbulent, naturally driven enclosure flow. The enclosure is a cubical cavity with side 0.7 m in which two opposite vertical walls are held at different temperatures while other walls are adiabatic. The transport of monodisperse SiO2 particles with diameter 0.5, 1.0, and 2.5 μm was studied at Rayleigh numbers varying in the range of 3 × 108 to 109, corresponding to temperature differentials ΔT from 10 to 40 K. The decay time constant of the airborne particle concentration was calculated from discrete measurements performed with an Electrical Low-Pressure Impactor. It is found that the temperature difference greatly influences the deposition of particles with sizes equal to or less than 1 μm in diameter. For this particle range, thermophoresis becomes important and hence the larger the ΔT, the larger the deposition, a significant part of which taking place on the cold wall by the thermophoretic effect. As a result, the decay time constant of submicron particles is up to 5 times smaller than predicted by the stirred settling model, depending on the imposed ΔT. For the largest particles with diameter 2.5 μm, the influence of thermophoresis and hence ΔT is negligible, and particle removal rates are in line with the stirred settling model predictions, with mostly gravity dominated deposition on the bottom wall. A Large Eddy Simulation of the tests was performed using an Euler-Lagrange approach, and predictions of the decay time constant are within less than 20% of the measured values.

Ground measurements of physical, chemical and hygroscopic properties of aerosols were made at the Olympic Park, Seoul, as part of the KORea-United States Air Quality study (KORUS-AQ) campaign in May–June 2016. The average number concentrations of aerosols larger than 10 nm in diameter and cloud condensation nuclei (CCN) at 0.6% supersaturation (S) were 10800 c m − 3 and 3400 c m − 3 , respectively. The average geometric mean diameter ( D g ) was 44 nm, and size-resolved aerosol hygroscopicity (κ) from HTDMA ranged from 0.11 to 0.24 for particle diameters in the range of 30–150 nm. Aerosols were classified into three types based on mixing state and hygroscopic growth factor (GF): Type 1 (externally mixed aerosol), Type 2 (Internally mixed and growth aerosol) and Type 3 (internally mixed and non-growth aerosol). These three aerosol types showed distinct diurnal patterns. The difference in physical and chemical properties of aerosols for different air mass sources crucially impacted aerosol hygroscopicity. Using the external mixture assumption with measured hygroscopicity data improved the results of CCN prediction compared to those from the simple internal mixture assumption because externally mixed aerosols comprised a significant portion of aerosols in this urban area. Moreover, the simple assumption of aerosol size distribution with a fixed chemical composition sufficiently explained more than 50 percent of the variation of CCN number concentrations, although the information of chemical composition was still meaningful. Overall, the measured data showed consistency with Megacity Air Pollution Studies (MAPS-Seoul) campaign held during May–June 2015, implying that these results may represent urban aerosols in spring/summer in the Korean Peninsula.

An Eulerian-Lagrangian 3D computational fluid dynamics (CFD) model of pesticide dust drift from precision vacuum planters in field conditions was developed. Tractor and planter models were positioned in an atmospheric computational domain, representing the field and its edges. Physicochemical properties of dust abraded from maize seeds (particle size, shape, porosity, density, a.i. content), dust emission rates and exhaust air velocity values at the planter fan outlets were measured experimentally and implemented in the model. The wind profile, the airflow pattern around the machines and the dust dispersion were computed. Various maize sowing scenarios with different wind conditions, dust properties, planter designs and vacuum pressures were simulated. Dust particle trajectories were calculated by means of Lagrangian particle tracking, considering nonspherical particle drag, gravity and turbulent dispersion. The dust dispersion model was previously validated with wind tunnel data. In this study, simulated pesticide concentrations in the air and on the soil in the different sowing scenarios were compared and discussed. The model predictions were similar to experimental literature data in terms of concentrations and drift distance. Pesticide exposure levels to bees during flight and foraging were estimated from the simulated concentrations. The proposed CFD model can be used in risk assessment studies and in the evaluation of dust drift mitigation measures.

This short communication investigated the characteristics and sources of refractory black carbon (rBC) aerosols using an Aerodyne soot-particle aerosol mass spectrometer (SP-AMS). The SP-AMS dataset acquired at suburban Nanjing observed carbon clusters (Cn+) up to n = 160, which was classified into three groups (low-C: C1+-C5+; mid-C: C6+-C31+; full-C (fullerenes): C32+-C160+). A simple method was first developed to reduce influences of organic molecules on the Cn+ signals. We found that the temporal variations of low-C and mid-C varied similarly, but were substantially different from full-C, indicating different source contributions. Furthermore, positive matrix factorization analyses showed that the C1+/C3+ ratios of traffic-, industry-, cooking-related rBC were 0.88, 1.29 and 0.01, respectively. We propose such C1+/C3+ ratios can be used as references to distinguish different sources for rBC in ambient conditions, yet further verifications with more field data are still required, and whether or not such ratios in rBC cores are stable upon atmospheric ageing remains to be elucidated.