Single Particle Aerosol Mass Spectrometry Research Articles

Single particle mass spectral signatures from on-road and non-road vehicle exhaust particles and their application in refined source apportionment using deep learning

With advances in vehicle emission control technology, updating source profiles to meet the current requirements of source apportionment has become increasingly crucial. In this study, on-road and non-road vehicle particles were collected, and then the chemical compositions of individual particles were analyzed using single particle aerosol mass spectrometry. The data were grouped using an adaptive resonance theory neural network to identify signatures and establish a mass spectral database of mobile sources. In addition, a deep learning-based model (DeepAerosolClassifier) for classifying aerosol particles was established. The objective of this model was to accomplish source apportionment. During the training process, the model achieved an accuracy of 98.49 % for the validation set and an accuracy of 93.36 % for the testing set. Regarding the model interpretation, ideal spectra were generated using the model, verifying its accurate recognition of the characteristic patterns in the mass spectra. In a practical application, the model performed hourly source apportionment at three specific field monitoring sites. The effectiveness of the model in field measurement was validated by combining traffic flow and spatial information with the model results. Compared with other machine learning methods, our model achieved highly automated source apportionment while eliminating the need for feature selection, and it enables end-to-end operation. Thus, in the future, it can be applied in refined and online source apportionment of particulate matter.

Analysis and identification of degradation products in gas, particle, and liquid phases of polypropylene and polyethyleneterephthalate microplastics aging through non-thermal plasma simulation.

Plastic aging can cause alterations in the physical and chemical characteristics of plastics, as well as their behavior in the environment. Due to the extremely slow natural aging process, laboratory simulated aging methods have to be used. In this study, non-thermal plasma (NTP) was adopted to investigate the aging process of polypropylene (PP) and polyethylene terephthalate (PET) microplastics. Various analytical instruments, including proton transfer reaction mass spectrometry and single-particle aerosol mass spectrometry, were employed to examine and identify the organic constituents of the gas, liquid, and particle phase degradation products, as well as to monitor the degradation process. The results showed that after 90min of aging, both PP and PET surfaces showed yellowing, and the carbonyl index of PP increased while that of PET decreased, with an increase in crystallinity. The organic components of reaction products, such as ketones, esters, acids, and alcohols, increased with longer aging times. Gas products mainly contain aromatic hydrocarbons, while particles from aged PET contain compounds with benzene rings and metal elements. Liquid products from aged PP show a significant presence of branched alkanes. Based on this analysis, degradation mechanisms of PP and PET by NTP were proposed. This investigation represents the initial systematically exploration of the release of organic substances during the degradation of microplastics mediated by NTP. It provides significant insights into the detrimental organic compounds emitted during this process, thereby offering valuable information for understanding the environmental and human health implications of natural microplastic degradation. Furthermore, it addressed the requirements for increased attention to the potential environmental risks associated with these harmful components.

Insights into the seasonal characteristics of single particle aerosols in Chengdu based on SPAMS

To investigate the seasonal characteristics in air pollution in Chengdu, a single particle aerosol mass spectrometry was used to continuously observe atmospheric fine particulate matter during one-month periods in summer and winter, respectively. The results showed that, apart from O3, the concentrations of other pollutants (CO, NO2, SO2, PM2.5 and PM10) were significantly higher in winter than in summer. All single particle aerosols were divided into seven categories: biomass burning (BB), coal combustion (CC), Dust, vehicle emission (VE), K mixed with nitrate (K-NO3), K mixed with sulfate and nitrate (K-SN), and K mixed with sulfate (K-SO4) particles. The highest contributions in both seasons were VE particles (24%). The higher contributions of K-SO4 (16%) and K-NO3 (10%) particles occurred in summer and winter, respectively, as a result of their different formation mechanisms. S-containing (K-SO4 and K-SN), VE, and BB particles caused the evolution of pollution in both seasons, and they can be considered as targets for future pollution reduction. The mixing of primary sources particles (VE, Dust, CC, and BB) with secondary components was stronger in winter than in summer. In summer, as pollution worsens, the mixing of primary sources particles with 62 [NO3]− weakened, but the mixing with 97 [HSO4]− increased. However, in winter, the mixing state of particles did not exhibit an obvious evolution rules. The potential source areas in summer were mainly distributed in the southern region of Sichuan, while in winter, besides the southern region, the contribution of the western region cannot be ignored.

In Situ Characterization of Bioaerosols at the Single-Particle Level Using Single-Particle Mass Spectrometry: A Promising Tool for Defending Human Health against Bioaerosol Transmission.

Bioaerosol transmission is one of the important transmission pathways of COVID-19 and other infectious respiratory diseases caused by viral infection. The ability to detect bioaerosols and characterize encapsulated pathogens both in situ and in real time is crucial for early warning and monitoring of the progress of an epidemic or pandemic. The lack of a powerful analytical tool for distinguishing between bioaerosols and nonbioaerosols as well as for identification of pathogen species contained in the bioaerosols is the bottleneck in related fields. Herein, a promising solution for in situ and real-time accurate and sensitive detection of bioaeorosols is proposed by integrating single-particle aerosol mass spectrometry, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and fluorescence spectroscopy. The proposed mass spectrometry aims at detecting bioaerosols in a range of 0.5-10 μm with adequate sensitivity and specificity. This single-particle bioaerosol mass spectrometry would not only be a powerful tool that can be useful for the authorities and public health monitoring but also would be an example of advances in mass spectrometry.

Online study of the plasma-accelerated aging process and toxicity of polyethylene terephthalate

Plastic aging occurs in all environmental media and affects their environmental behavior and toxicity. In this study, non-thermal plasma was applied to simulate the aging process of plastics, with polyethylene terephthalate (PET-film) being used as a model. The surface morphology, mass defects, toxicity of aged PET-film and the generation of airborne fine particles were comprehensively characterized. The surface of PET films began to become rough and then gradually became uneven, generating pores, protrusions and cracks. The toxicity of aged PET films was assessed in Caenorhabditis elegans which significantly reduced head thrashing, body bending and brood size. A single particle aerosol mass spectrometry instrument was used to characterize the size distribution and chemical composition of airborne fine particles in real-time. Few particles were observed during the first 90 min, while the generation of particles accelerated significantly after aging time beyond 90 min. For two pieces of PET film with surface area of 5 cm2, during the 180 min, at least 15113 ± 153 fine particles were generated, having a unimodal size distribution with a peak of 0.4 µm. The main components of these particles included metals, inorganic non-metals, and organic components. The results provide useful information on plastic aging and are beneficial in assessing the potential environmental risks.

Sulfate formation via aerosol-phase SO2 oxidation by model biomass burning photosensitizers: 3,4-dimethoxybenzaldehyde, vanillin and syringaldehyde using single-particle mixing-state analysis

Abstract. Atmospheric oxidation of sulfur dioxide (SO2) to sulfate has been widely investigated by means of gas-phase and in-cloud chemistry studies. Recent field measurements have shown significant sulfate formation in cloud-free environments with high aerosol loadings. As an important fraction of biomass burning aerosol components, particulate phenolic and non-phenolic aromatic carbonyls may initiate photosensitized multiphase oxidation of SO2 in aerosols, of which our knowledge however is still in its nascent stage. In this study, on the basis of single-particle aerosol mass spectrometry (SPAMS) measurements, we find evident sulfate formation in the biomass-burning-derived photosensitizer particles under UV and SO2 exposure, attributable to photosensitized oxidation of S(IV), while almost no sulfate was observed under dark conditions. The efficiency of sulfate production by photosensitizer particles under UV irradiation, represented by the number percentage of sulfate-containing particles (99 %–43 %) and the relative peak area (RPA) of sulfate (0.67–0.12) in single-particle spectra, in descending order, were 3,4-dimethoxybenzaldehyde (DMB), vanillin (VL) and syringaldehyde (SyrAld). Internal mixtures of VL and potassium nitrate (KNO3) gave a slightly lower number percentage and RPA of sulfate than VL particles alone. In externally mixed VL and KNO3 particles, sulfate was predominantly formed on the former, confirming that sulfate formation via photosensitization prevails over that via nitrate photolysis. Our results suggest that photosensitized oxidation of S(IV) could make an important contribution to aerosol sulfate formation, especially in areas influenced by biomass burning.

Size–resolved mixing state of ambient refractory black carbon aerosols in Beijing during the XXIV Olympic winter games

Atmospheric loading of black carbon aerosols influences air quality and visibility, and their mixing state and aerosol chemistry were sensitive to both emission scenarios and regional transport. In this study, the aerodynamic size-resolved mixing state of refractory black carbon aerosols (rBC) was investigated using a novel tandem system consisting of an aerodynamic aerosol classifier (AAC), a single particle soot photometer (SP2), and single-particle-aerosol mass spectrometry (SPA-MS) during the XXIV Olympic Winter Games (OWG) at an urban site in Beijing. Particles with aerodynamic diameter (Dae) of 200 nm and 300 nm were selected by AAC to focus on the effect of relative differences in morphology on the coating thickness, coating compositions, and optical properties of rBC particles. We found that rBC-containing particles with Dae of 300 nm were characterized by a rBC core with a count median diameter (CMD) of 108 ± 4 nm that typically have regular morphology (χ:mean∼1), higher relative coating thickness (RCT: mean ∼1.9), and strong light absorption enhancement (Eabs: mean ∼1.5). The rBC-containing particles with Dae = 200 nm normally had irregular shapes (χ:mean∼1.4) and weak Eabs (Eabs: mean ∼1.37). Classification based on air mass clustering and air pollution level revealed that the coating thickness of rBC particles only exhibited unimodal patterns under clean air conditions and distinct bimodal distributions under heavy pollution conditions, implying multiple origins of rBC particles, even during OWG periods. The coating thickness and Eabs of rBC particles were greater when influenced by the higher RH air from east. Furthermore, the chemical compositions of the rBC coating quantitatively determined by SPA-MS were used to estimate the possible origins of the Dae = 300 nm, featured by a thicker coating thickness and stronger light absorption enhancement. Our results showed that rBC particles were primarily mixed with organics, nitrate, and sulfate during the XXIV OWG period. The organic components have a limited role in increasing rBC coatings under polluted conditions, while the alkali metal ions (K and Na) associated with traffic emissions and the secondary inorganic species favor the formation of thick coatings. Higher RH makes limited contributions to rBC mixed with sulfate and organics only (BCOC*_S) and pure BC. The relatively fresh BC could directly mix with organics and sulfate at low RH levels while evolving to mix with nitrate at high RH conditions. In addition to high concentrations of locally emitted precursors and high RH that tend to form thick coatings of nitrate-related rBC aerosols, secondary transport from the west and southwest also contributes to rBC aerosols mixed with nitrate with relatively thick coatings.

Smog chamber study of secondary organic aerosol formation from gas- and particle-phase naphthalene ozonolysis

Naphthalene (Nap), one of the most abundant PAHs in the atmosphere, has been shown to be an important secondary organic aerosol (SOA) precursor. In this study, the gas- and particle-phases (Suspended Nap-coated polystyrene latex spheres (PSLs) generated by vaporization condensation) Nap ozonolysis were investigated in a 1000 L volume cubic Teflon smog chamber. Gas-phase products and Nap-SOAs were observed from the gas- and particle-phase Nap ozonolysis via homogeneous and heterogeneous reactions, respectively. The time-dependent size distribution and mass concentration of Nap-SOAs were analyzed using a scanning mobility particle sizer and a laboratory-developed single-particle aerosol mass spectrometry (SPAMS) instrument. The chemical components of the homogeneous and heterogeneous reaction products were analyzed on-line by single photo ionization mass spectrometry (SPIMS), SPAMS, as well as by thermal desorption gas chromatograph-mass spectrometry. The results showed that the chemical components of the gas-and particle-phase Nap ozonolysis were essentially the same, with the dominant products being phthalaldehyde, phthalic anhydride, 2-carboxybenzaldehyde, and benzoic acid; Nap-SOA formation was attributed to the formation of new particles as well as the uptake of homogeneous and heterogeneous Nap oxidation products on the gas-phase or/and the particle surface. Based on the online measurement results, the reaction mechanism of Nap-ozonolysis also exhibits an initial carbon atom or double-bond attacks by O3, and kinetic analysis of Nap-coated PSLs ozonolysis shows a heterogeneous reaction rate constant of 2.55E-4 s−1 with R2 = 0.984. This study provides a systematic approach to characterize the chemical and physical properties of the gas- and particle-phase Nap ozonolysis in real time, which will deepen our understanding of the migration and transformation of PAHs in the atmosphere.

Effect of COVID-19 lockdown on the characterization and mixing state of carbonaceous particles in the urban atmosphere of Liaocheng, the North China Plain

To investigate the effect of COVID-19 control measures on aerosol chemistry, the chemical compositions, mixing states, and formation mechanisms of carbonaceous particles in the urban atmosphere of Liaocheng in the North China Plain (NCP) were compared before and during the pandemic using a single particle aerosol mass spectrometry (SPAMS). The results showed that the concentrations of five air pollutants including PM2.5, PM10, SO2, NO2, and CO decreased by 41.2%–71.5% during the pandemic compared to those before the pandemic, whereas O3 increased by 1.3 times during the pandemic because of the depressed titration of O3 and more favorable meteorological conditions. The count and percentage contribution of carbonaceous particles in the total detected particles were lower during the pandemic than those before the pandemic. The carbonaceous particles were dominated by elemental and organic carbon (ECOC, 35.9%), followed by elemental carbon-aged (EC-aged, 19.6%) and organic carbon-fresh (OC-fresh, 13.5%) before the pandemic, while EC-aged (25.3%), ECOC (17.9%), and secondary ions-rich (SEC, 17.8%) became the predominant species during the pandemic. The carbonaceous particle sizes during the pandemic showed a broader distribution than that before the pandemic, due to the condensation and coagulation of carbonaceous particles in the aging processes. The relative aerosol acidity (Rra) was smaller before the pandemic than that during the pandemic, indicating the more acidic particle aerosol during the pandemic closely related to the secondary species and relative humidity (RH). More than 95.0% and 86.0% of carbonaceous particles in the whole period were internally mixed with nitrate and sulfate, implying that most of the carbonaceous particles were associated with secondary oxidation during their formation processes. The diurnal variations of oxalate particles and correlation analyses suggested that oxalate particles before the pandemic were derived from aqueous oxidation driven by RH and liquid water content (LWC), while oxalate particles during the pandemic were originated from O3-dominated photochemical oxidation.

Ambient particle characteristics by single particle aerosol mass spectrometry at a coastal site in Hong Kong: a case study affected by the sea-land breeze.

The sea-land breeze (SLB) circulation plays a vital role in the transport of atmospheric pollutants in coastal cities. In this study, a single particle aerosol mass spectrometer (SPAMS) and combined bulk aerosol instruments were deployed to investigate the ambient particle characteristic at a suburban coastal site in Hong Kong from February 22 to March 10, 2013. Significant SLB circulations were captured from March 6-10, 2013, during the campaign. During the SLB periods, air quality worsened, with PM2.5 concentrations reaching a peak of 55.6 μg m-3 and an average value of 42.8 ± 4.5 μg m-3. A total of 235,894 particles were measured during the SLB stage. Eight major sources were identified by investigating the mixing states of the total particles, including the coal-burning related particles (48.1%), biomass burning particles (6.7%), vehicle emission-related particles (16.4%), sea salt (9.2%), ship emission particles (2.7%), dust/steeling industries (3.7%), waste incineration (6.3%), and road dust (3.9%). It was noteworthy that the PM2.5 concentrations and particle numbers increased sharply during the transition of land wind to the sea breeze. Meanwhile, the continental sourced pollutants recirculated back to land resulting in a cumulative increase in pollutants. Both individual and bulk measurements support the above results, with high contributions from coal burning, biomass burning, bulk K+, and NO3 -, which were probably from the regional transportation from the nearby area. In contrast, the ship and vehicle emissions increased during the SLB period, with a high sulfate concentration partially originating from the ship emission. In this study, field evidence of continental-source pollutants backflow to land with the evolution of sea breeze was observed and helped our current understanding of the effect of SLB on air quality in the coastal city.

Laser-driven ionization mechanisms of aluminum for single particle aerosol mass spectrometry

Single particle aerosol mass spectrometry (SPAMS), an analytical technique for measuring the size and composition of individual micron-scale particles, is capable of analyzing atmospheric pollutants and bioaerosols much more efficiently and with more detail than conventional methods which require the collection of particles onto filters for analysis in the laboratory. Despite SPAMS’ demonstrated capabilities, the primary mechanisms of ionization are not fully understood, which creates challenges in optimizing and interpreting SPAMS signals. In this paper, we present a well-stirred reactor model for the reactions involved with the laser-induced vaporization and ionization of an individual particle. The SPAMS conditions modeled in this paper include a 248 nm laser which is pulsed for 8 ns to vaporize and ionize each particle in vacuum. The ionization of 1 μm, spherical Al particles was studied by approximating them with a 0-dimensional plasma chemistry model. The primary mechanism of absorption of the 248 nm photons was pressure-broadened direct photoexcitation to Al(y2D). Atoms in this highly excited state then undergo superelastic collisions with electrons, heating the electrons and populating the lower energy excited states. We found that the primary ionization mechanism is electron impact ionization of various excited state Al atoms, especially Al(y2D). Because the gas expands rapidly into vacuum, its temperature decreases rapidly. The rate of three-body recombination (e− + e− + Al+ → Al + e−) increases at low temperature, and most of the electrons and ions produced recombine within several μs of the laser pulse. The importance of the direct photoexcitation indicates that the relative peak heights of different elements in SPAMS mass spectra may be sensitive to the available photoexcitation transitions. The effects of laser intensity, particle diameter, and expansion dynamics are also discussed.

Characterization of Fe-containing particles in Chengdu, southwest China, using single-particle aerosol mass spectrometry

Single-particle aerosol mass spectrometry was used to study the characteristics of Fe-containing particles during winter in Chengdu, southwest China. The mass concentrations of PM2.5 and PM10 during the study period were 64 ± 38 and 89 ± 49 µg/m3, respectively, and NO2 and particulate matter were high compared with most other regions of China. The Fe-containing particles were divided into seven categories with different mass spectra, sources and aging characteristics. The highest contribution was from Fe mixed with carbonaceous components (Fe-C, 23.1%) particles. Fe was more mixed with sulfate than nitrate and therefore the contribution of Fe mixed with sulfate (Fe-S, 20.7%) particles was higher than that of Fe mixed with nitrate (Fe-N, 12.5%) particles. The contributions from Fe-containing particles related to primary combustion were high in the small particle size range, whereas aged Fe-containing particles and dust-related particles were mostly found in the coarse particle size range. The air masses mainly originated from the west and east of Chengdu, and the corresponding PM2.5 concentrations were 79 ± 36 and 55 ± 36 µg/m3, respectively. The west and east air masses showed stronger contributions of Fe-containing particles related to biomass burning (Fe-B) and fossil fuel combustion (Fe-C and Fe-S) particles, respectively. The southwest area contributed the most Fe-containing particles. Future assessments of the effects of Fe-containing particles during heavy pollution period should pay more attention to Fe-C and Fe-S particles. Emission-reduction of Fe-containing particles should consider both local emissions and short-distance transmission from the surrounding areas.

Real-time single particle characterization of oxidized organic aerosols in the East China Sea

Knowledge of the chemical characteristics and sources of organic aerosols (OA) over marine is needed for evaluating their effects on climate change and air quality. Here, a quadrupole aerosol chemical speciation monitor (Q-ACSM) and a single-particle aerosol mass spectrometry (SPAMS) were synchronously employed to investigate the chemical composition, mixing state, and oxidation degree of oxidized organic aerosols (OOA) in PM1 over the East China Sea (ECS) from 3 to 27 June 2017. Both aerosol mass spectrometers demonstrated that a higher oxidation state of OOA in aerosol particles could be generated during marine air mass-dominated periods (MDP) than that generated during land air mass-dominated periods (LDP). Two OOA factors including semi-volatile oxidized organic aerosol (SV-OOA) and low-volatility oxidized organic aerosol (LV-OOA) were distinguished based on Q-ACSM. Fifty-seven percent of the total detected particles with obvious signals of organic markers were identified as oxidized organic carbon (OOC) particles via SPAMS and further divided into lower oxidized organic carbon (LOOC) particles and more oxidized organic carbon (MOOC) particles. All OOC-containing particles were clustered into seven particle subgroups. The EC and K subgroups dominated the LOOC and MOOC particles, respectively, during periods controlled by land air masses, indicating that notable OOC formation was influenced by continental sources. OOA with higher oxygen states were found to dominate near ports. This suggested that OOA chemical characteristics over the ESC are seriously affected by continental, ship, and port emissions, which should be synergistically considered in evaluating their effects on solar radiation transfer and cloud processes.

Structurally characterized aluminum alkoxide derivatives for aerosol spray materials production

The synthesis of a family of aluminum alkoxides was undertaken via the reaction of trimethyl aluminum (Al(CH3)3) using a series of sterically varied ortho-substituted phenols (H-OAr), including: 2-methyl phenol (H-oMP), 2-isopropyl phenol (H-oPP), 2-phenyl phenol (H-oPhP), 2,6-di-methyl phenol (H-DMP), 2,6-di-isopropyl phenol (H-DIP), and 2,6-di-phenyl phenol (H-DPhP). The products isolated using the least sterically encumbered phenoxides proved to generate the homoleptic compounds: [(oMP)Al((μ-oMP)2Al(oMP)2)2] (1), and [Al(μ-oPP)(oPP)2]2 (2), [Al(μ-oPP)(oPP)2(THF)]2 (2-THF), and [Al(μ-oPhP)(oPhP)2]2 (3). As the steric bulk was increased only partial substitution was achieved forming the alkyl, alkoxide compounds: [Al(μ-OAr)(CH3)(OAr)]2 (OAr = trans-DMP (4a), cis-DIP (5a), trans-DPhP (6a)). Sub-stoichiometric metathesis reactions for the smaller OAr ligands were undertaken to produce a series of [Al(CH3)3-x(OAr)x]2 where × = 2: OAr = trans-oMP (1a); x = 1, OAr = oMP (1b), and DMP (4b). Alternatively, the use of neo-pentanol (H-ONep) led to the homoleptic species [(ONep)Al((μ-ONep)2Al(ONep)2)2] (7) and heteroleptic [Al(μ-ONep)(CH3)2]2 (7b). Efforts to generate 7 from [Al(OPri)3]4 resulted in the production of the mixed ligated species [Al4(μ-OPri)6(ONep)6] (8). The compounds were fully characterized using a variety of analytical tools as well as multinuclear NMR (1H, 13C, 27Al) spectroscopy. Select species were used for aerosol spray pyrolysis for the anticipated production of alumina (Al2O3) materials. The final products from 1, 1b, 7, and 7b proved to generate amorphous mesoparticles of size 2.1(0.1), 2.6(0.2), 2.7(0.2), and 2.5(0.2) μm, respectively as determined by SEM and pXRD analyses. Data collected using Single Particle Aerosol Mass Spectrometry (SPAMS) revealed that Al0 particles had been produced instead of the expected Al2O3 ceramic materials.

Influence of Ambient Atmospheric Environments on the Mixing State and Source of Oxalate-Containing Particles at Coastal and Suburban Sites in North China

Photodegradation is a key process impacting the lifetime of oxalate in the atmosphere, but few studies investigated this process in the field due to the complex mixing and sources of oxalate. Oxalate-containing particles were measured via single-particle aerosol mass spectrometry at coastal and suburban sites in Qingdao, a coastal city in North China in the summer of 2016. The mixing state and influence of different ambient conditions on the source and photodegradation of oxalate were investigated. Generally, 6.3% and 12.3% of the total particles (by number) contained oxalate at coastal and suburban sites, respectively. Twelve major types of oxalate-containing particles were identified, and they were classified into three groups. Biomass burning (BB)-related oxalate–K and oxalate–carbonaceous particles were the dominant groups, respectively, accounting for 68.9% and 13.6% at the coastal site and 72.0% and 16.8% at the suburban site. Oxalate–Heavy metals (HM)-related particles represented 14.6% and 9.3% of the oxalate particles at coastal and suburban sites, respectively, which were mainly from industrial emissions (Cu-rich, Fe-rich, Pb-rich), BB (Zn-rich), and residual fuel oil combustion (V-rich). The peak area of oxalate at the coastal site decreased immediately after sunrise, while it increased during the daytime at the suburban site. However, the oxalate peak area of Fe-rich particles at both sites decreased after sunrise, indicating that iron plays an important role in oxalate degradation in both environments. The decay rates (k) of Fe-rich and BB-Fe particles at the coastal site (−0.978 and −0.859 h−1, respectively), were greater than those at the suburban site (−0.512 and −0.178 h−1, respectively), owing to the high-water content of particles and fewer oxalate precursors. The estimated k values of oxalate peak area for different ambient conditions were in the same order of magnitude, which can help establish or validate the future atmospheric models.

Characteristics and pollution formation mechanism of atmospheric fine particles in the megacity of Chengdu, China

To investigate the characteristics and pollution formation mechanism of fine particles in the atmosphere of Chengdu, one of the cities most affected by haze in China, ambient single aerosol particles were measured by single particle aerosol mass spectrometry from April to May 2021. All particles collected during the study period could be divided into seven categories: Dust, vehicle emission (VE), biomass burning (BB), coal combustion (CC), organic carbon (OC), K-nitrate (KNO3) and K-sulfate (KSO4) particles. BB and VE particles contributed 29.2% and 25.0% to the total particles, respectively, and these two types of particles can be used as the focus of pollution reduction in the future. The mixed state analysis showed that all types of particles highly mixed with their tracer ions, and the non secondary inorganic particles (i.e., Dust, VE, BB, CC and OC particles) showed stronger mixing with nitrate than sulfate. The increase of PM2.5 concentration can be divided into three stages, and the increase of PM2.5 concentration in these three stages was dominated by Dust and OC particles, BB and KNO3 particles, and the remaining three types of particles, respectively. The air masses mainly originated from the area northeast of Chengdu, while the southwest trajectory corresponded to the highest PM2.5 and PM10 concentrations. Meanwhile, the potential source areas of the different types of particles were different and the area southwest of Chengdu was the most important potential source of PM2.5 and of most particle types.

Characterization of the spatial and temporal distribution of lead around a battery industrial park by LA-SPAMS

A convenient technique for direct solids analysis, laser ablation single particle aerosol mass spectrometry (LA-SPAMS), was used to investigate lead and other components in soil and bark samples from around a battery industrial park. In total, over 50,000 particles ranging in size from 0.2 to 2 μm were sampled and approximately 15–35% of the particles were analyzed for chemical composition. The mean mass spectrum results showed that the intensity of lead varied widely among sampling points, reaching the highest intensity in the topsoil and bark at sampling point 4, located closest to the core factory. Based on the neural network algorithm of adaptive resonance theory (ART-2a), the topsoil and bark samples were classified into five categories: crustal composition (Ca+, silicates, aluminates, etc.), elemental carbon (C2-, C3−, C4−, etc.), organic carbon (CN−, levoglucosan, etc.), secondary inorganic sources (phosphates, nitrates, sulfates), and heavy metals (Pb+, Zn+, Cu+), with the proportion of Pb varying from 0.020 to 0.25% and 0.030–9.41% in topsoil and bark samples, respectively, while the proportion of Cu and Zn in topsoil and bark samples did not differ as greatly as Pb. In addition, the particle number concentrations of lead particles in topsoil and bark ranged from 0.14 to 3.48% and 0.36–37.93%, respectively. The concentrations of Pb in topsoil and bark samples measured by ICP-OES varied from 71 to 791 ppm and 172–2595 ppm, respectively. Overall, both the lead content in topsoil samples measured by LA-SPAMS and ICP-OES reached maximum values at sampling points 4 and 5, respectively, indicating moderate pollution with Pb at these two sites. This convenient LA-SPAMS method not only accurately detects the composition of solid samples, the mixing state of particulate matter, and the analytical component sources, but also omits tedious pretreatment steps, reduces the use of organic solvents, and shortens the detection time of solid samples, thereby providing an attractive method for soil environmental quality monitoring.

Dry-deposition of inorganic and organic nitrogen aerosols in Xiamen Bay: Fluxes, sources, and biogeochemical significance

Increased dry deposition of nitrogen aerosols (aerosol-N) as a result of anthropogenic emissions has caused large negative impacts on marine ecosystems. We monitored the number concentrations and sizes of inorganic nitrogen aerosols (aerosol-IN: NH4+ and NO3−) and organic nitrogen aerosols (aerosol-ON: methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine) by single-particle aerosol mass spectrometry (SPAMS) during the warm season (WS) and cold season (CS) of 2013 and 2015 in Xiamen Bay. The mean hourly number concentration of aerosol-IN (874/h) overwhelmed that of aerosol-ON (103/h), accounting for 83.9 ± 16.1% of aerosol-N. More than 90% of aerosol-N was concentrated in the condensation mode (0.1–0.5 μm) and droplet mode (0.5–2.0 μm). Aerosol-IN was the main contributor (80.1–94.2%) to aerosol-N deposition. New production potentially supported by the ocean's external nitrogen supply provided aerosol-N input of 11.51–11.96 g C m−2 yr−1, which contributed 17.5–18.2% of total new production in the southern East China Sea. Four potential sources of aerosol-N were identified based on the results of positive matrix factorization analysis, including secondary formation (F1), biogenic source (F2), sea spray, soil dust, biomass burning (F3), and anthropogenic sources (F4). Aerosol-N concentrations in Xiamen Bay were mainly affected by the ocean air masses during the WS and inland air masses during the CS. The percentages of aerosol-N at each backward trajectory cluster showed that the inland air masses brought more aerosol-IN emitted from biomass burning, soil dust, and secondary formation sources, whereas the ocean air masses brought more aerosol-ON emitted from a marine biogenic source into Xiamen Bay. This study provides an example of determining the number concentrations and sizes of IN and ON in aerosols by SPAMS, and helps us further understand the dry deposition and sources of IN and ON in aerosols in Xiamen Bay.

Effects of Volatile Components on Mixing State and Size Distribution of Individual Black Carbon Aerosols

In this study, the effects of different volatile components on the mixing state and size distribution of ambient individual black carbon (BC) aerosols were measured using thermo-denudation with single-particle soot photometry and single-particle aerosol mass spectrometry from September 9 to September 27, 2018, in Shanghai, China. The volatility, chemical composition, size distribution, and core-shell structure of BC aerosol were also analysed. To understand the influence of heating temperature on the BC core-shell structure, the mixing state of ageing particles at room temperature (25°C) and the mixing state of residual material heated to 150°C and 300°C were analysed. BC was internally mixed with secondary components, such as ammonium nitrate, ammonium sulphate, a small amount of sodium nitrate, potassium nitrate, sodium sulphate and potassium sulphate, and other nonvolatile components. At 300°C, the secondary components with low volatility escaped, resulting in a thinner BC coating. However, several low-volatile non-BC substances remained, namely organic species, potassium chloride, potassium nitrate, and other nonvolatile substances. The extremely strong photochemical reaction may have produced large amounts of secondary organic carbon on the BC surface in the afternoon, with the high temperature volatilising the whole particle. However, fresh BC particles emitted from traffic during morning rush hour had ultralow volatility, with relatively fewer low-volatile components on the surface.

Interannual evolution of elemental carbon-containing particles in winter in the atmosphere of Chengdu, China

As one of the important components of PM2.5, elemental carbon (EC) particles could quickly mix with other organic or inorganic species after entering the atmosphere, which directly affected its climate and environmental effects and impact on human health. In order to study the mixture and evolution of EC particles in the atmosphere, this study used single particle aerosol mass spectrometry to measure the EC-containing particles in three winters (2016/17, 2018/19 and 2019/20) in Chengdu, one of the most polluted megacities in China. The results showed that the average mass concentrations of PM2.5 in the three winters were 121 ± 58 μg m−3, 90 ± 32 μg m−3 and 79 ± 38 μg m−3, respectively, and the mass ratios of PM2.5/PM10 were 0.71, 0.78 and 0.78, respectively. EC-containing particles accounted for 40.7%–54.7% of all particles and could be divided into six categories: EC-dust (EC-D), fresh EC (ECf), EC-organic carbon (EC-OC), EC-nitrate (EC-N), EC-sulfate (EC-S) and EC-sulfate-nitrate (EC-SN). From winter 2016/17 to 2019/20, the contributions of EC-N and EC-OC particles increased, while the contributions of EC-S and EC-SN particles decreased. Meanwhile, EC-N particles became increasingly important for the formation of heavy pollution. Photochemical and liquid-phase processes dominated the formation of EC-N and EC-S particles, respectively, while the dominant formation mechanism of EC-SN particles changed from photochemical to liquid-phase processes from winter 2016/17 to 2019/20. Total EC and EC-S particles in Chengdu were mainly transported from the east and southeast areas to Chengdu, while ECf particles mainly derived from local emissions. Compared with the previous two winters, the potential source areas of the EC-containing particles in winter 2019/20 reduced significantly. These findings provide new insight into the atmospheric behavior of urban particles and are important reference for the study of EC particles in other regions in the world, especially in urban areas.