Detection of polycyclic aromatic hydrocarbons using a high performance-single particle aerosol mass spectrometer

Unequal toxic effects of size-segregated single particles emitted from typical industrial plants, vehicles, and road dust

The health risks of particulate matters (PMs) associated with their chemical components and sizes have attracted increasing attention. However, the toxic effect of critical toxic components in size-segregated PMs from specific emission source remains unclear. We present the toxicity of size-segregated elements in PMs via integrating toxic analysis and online single-particle measurements of real-world industrial plants, vehicles, and road dust. The number fractions of elemental carbon (EC)- and Fe-containing particles were 5-11 and 3-12 folds greater than those of other metal-containing particles, respectively. A unimodal distribution with the peak at 0.4 µm was observed for the toxic metals emitted from industrial plants and road dust, while the distribution was relatively flat for vehicles. When integrating the abundance with toxicity of metals, especially Mn, Cu, V, and Fe, the peak for PM toxicity occurred at 0.4 µm for road dust, 0.4-0.7 µm for industrial plants, and 0.8 µm for vehicle-emitted PM. The inhalation risk in the alveolar region increased for these source-emitted PMs due to the efficient deposition of toxic PMs within 0.4-0.8 µm. These results reveal the complex coupling of health risks and size distributions of PMs, and further highlight that the health-oriented control of air pollution should consider PM1.

Mapping the constituent preference of tree species for capturing particulate matter on leaf surfaces using single-particle mass spectrometry and supervised machine learning

Respiratory health is negatively influenced by the dimensions and constituents of particulate matter (PM). Although mass concentration is widely acknowledged to be key to assessing dust retention by urban trees, the role of plant leaves in filtering PM from the urban atmosphere, particularly regarding the particle dimensions and chemical constituents of retained PM on the leaf, remains elusive. Here we combined single-particle aerosol mass spectrometry and a particle resuspension chamber to investigate how urban tree species capture PM constituents. Results indicate that leaves are efficient in capturing relatively larger particles (1.0-2.0 μm). Compositionally, airborne particles were mostly composed of elemental carbon (EC, 20%), organic carbon (OC, 17%), and secondary reaction products (13%). However, leaf surfaces revealed a preference for retaining crustal species, comprising 55% of captured particulates. Notably, specific tree species demonstrated varied affinities for different PM constituents: Osmanthus fragrans Lour. predominantly captured levoglucosan (LEV), indicative of its efficiency against biomass burning particles, whereas Cinnamomum camphora (L.) J.Presl and Sabina chinensis var. kaizuca W.C.Cheng & W.T.Wang were more effective in capturing heavy metals (HMs). XGBoost modelling identified indicator ions, e.g., CN-, NO3-, NO2-, PO3-, with SHAP values surpassing 0.035, suggesting a preferential adsorption of these ions among different tree species. These findings demonstrate that the particulate capture efficiency of urban tree species varies with species-specific leaf properties, particularly in their ability to selectively adsorb particles containing hazardous constituents such as LEV and HMs. This study provides a scientific basis for the strategic selection of tree species in urban forestry initiatives aimed at improving air quality and public health.

Mixing state and influence factors controlling diurnal variation of particulate nitrophenol compounds at a suburban area in northern China

Nitrophenols have received extensive attention due to their strong light-absorbing ability in the near-ultraviolet-visible region, which could be influenced by the atmospheric processes of nitrophenols. However, our knowledge and understanding of the formation and evolution of nitrophenols are still in the nascent stages. In the present study, the mixing states of four mononitrophenol particles (i.e., nitrophenol, methynitrophenol, nitrocatechol, and methoxynitrophenol), and one nitropolycyclic aromatic hydrocarbon particles (i.e., nitronaphthol (NN)) were investigated using a single-particle aerosol mass spectrometer (SPAMS) in November 2019 in Qingdao, China. The results showed, for the first time, that mononitrophenols and NN exhibit different mixing states and diurnal variations. Four mononitrophenols were internally mixed well with each other, and with organic acids, nitrates, potassium, and naphthalene. The diurnal variation in the number fraction of mononitrophenols presented two peaks at 07:00 to 09:00 and 18:00 to 20:00, and a valley at noon. Atmospheric environmental conditions, including NO2, O3, relative humidity, and temperature, can significantly influence the diurnal variation of mononitrophenols. Multiple linear regression and random forest regression models revealed that the main factors controlling the diurnal variation of mononitrophenols were photochemical reactions during the day and aqueous-phase reactions during the night. Unlike mononitrophenols, about 62-83% of NN were internally mixed with [NH4]+ and [H(NO3)2]-, but not with organic acids and potassium. The diurnal variation of NN was also different from that of mononitrophenols, generally increased from 17:00 to 10:00 and then rapidly decreaed from 11:00 to 16:00. These results imply that NN may have sources and atmospheric processes that are different from mononitrophenols. We speculate that this is mostly controlled by photochemical reactions and mixing with [NH4]+, which may influence the diurnal variation of NN in the ambient particles; however, this requires further confirmation. These findings extend our current understanding of the atmospheric formation and evolution of nitrophenols.

Determination of policyclic aromatic compounds, (PAH, nitro-PAH and oxy-PAH) in soot collected from a diesel engine operating with different fuels

A qualitative and quantitative analysis of polycyclic aromatic compounds (PACs; polycyclic aromatic hydrocarbons (PAHs), oxygenated and nitrated polycyclic aromatic hydrocarbons (OPAHs and NPAHs)) present in the soluble organic fraction (SOF) of different soot samples has been carried out to determine the effect of soot-generation conditions on their composition and health effects. The soot samples were generated using a diesel engine bench powered by diesel (DS) and biodiesel (BS) fuels under different combustion conditions. To optimize the procedure, a surrogate soot (Printex-U) and a certified reference material (SRM1650b) were also tested. Different extraction methods were used to extract the PAHs, OPAHs and NPAHs, and the Soxhlet technique using pyridine:acetic acid 1 % was found to be the most suitable procedure to extract the highest concentration (ng mg-1) and more types of PAHs and OPAHs from the soot. The results show that the PACs identified, and their concentrations, depend on the formation and collection conditions. The predominant compounds in all soot samples studied were fluorene (Flo), phenanthrene (Phe), fluoranthene (Fla), pyrene (Pyr), 9-fluorenone (9Flo) and 9,10-anthraquinone (9,10Anq). As such, the presence of these PACs in the atmosphere of urban and rural areas can mainly be attributed to the emissions from diesel vehicles. The percentage of OPAHs with respect to total PACs was highest in the soot generated from a biofuel. These oxidized compounds favor regeneration of the diesel particulate filter (DPF). The results also indicate that the carcinogenicity of the soot depends on the combustion conditions and type of fuel.

Brake wear-derived particles: Single-particle mass spectral signatures and real-world emissions

Brake wear is an important but unregulated vehicle-related source of atmospheric particulate matter (PM). The single-particle spectral fingerprints of brake wear particles (BWPs) provide essential information for understanding their formation mechanism and atmospheric contributions. Herein, we obtained the single-particle mass spectra of BWPs by combining a brake dynamometer with an online single particle aerosol mass spectrometer and quantified real-world BWP emissions through a tunnel observation in Tianjin, China. The pure BWPs mainly include three distinct types of particles, namely, Ba-containing particles, mineral particles, and carbon-containing particles, accounting for 44.2%, 43.4%, and 10.3% of the total BWP number concentration, respectively. The diversified mass spectra indicate complex BWP formation pathways, such as mechanical, phase transition, and chemical processes. Notably, the mass spectra of Ba-containing particles are unique, which allows them to serve as an excellent indicator for estimating ambient BWP concentrations. By evaluating this indicator, we find that approximately 4.0% of the PM in the tunnel could be attributable to brake wear; the real-world fleet-average emission factor of 0.28 mg km^-1 veh^-1 is consistent with the estimation obtained using the receptor model. The results presented herein can be used to inform assessments of the environmental and health impacts of BWPs to formulate effective emissions control policies.

Insights into the different mixing states and formation processes of amine-containing single particles in Guangzhou, China

The formation processes of particulate amines are closely related to their emission sources and secondary reactions, which can be revealed through the investigation of their real-time mixing states in individual particles. The mixing states of methylamine (MA)-, trimethylamine (TMA)-, and diethylamine (DEA)-containing particles were studied using a high-performance single particle aerosol mass spectrometer (HP-SPAMS) in Guangzhou, China, in January 2020. The sharp increase in TMA particles was found to be closely associated with the increase in the ambient relative humidity (RH), while the MA- and DEA-containing particles were not similarly influenced by the changes in the RH. The prominent enrichment of secondary oxygenated organics in DEA particles during the daytime was consistent with the active period of photochemistry, implying that the sharp decrease in DEA particles in the afternoon was likely due to photo-oxidation of the DEA. The number fraction (N_f) of DEA particles, the N_f of the nitrate in the DEA particles, and the abundance of nitrate increased as the NO_x content all increased during the nighttime, suggesting that the formation of DEA·HNO₃ salt was the dominant pathway of particulate DEA production. These results are consistent with our previous measurements in Nanjing, confirming the general and distinct mixing states of TMA and DEA particles. Positive matrix factorization analysis revealed that the total fraction of the more oxidized organics factor and the less oxidized organics factor were much higher in the DEA particles (26.9 %) than in the TMA particles (9 %), confirming the significant enrichment of oxygenated species in the DEA particles. The different mixing states of the amines revealed the unique response of each type of amine to the same atmospheric environment, and the prominent mixing states of the DEA with secondary oxygenated species suggest the potential role of DEA in tracing the evolution of organic aerosols.

Measurement of the mixing state of PAHs in individual particles and its effect on PAH transport in urban and remote areas and from major sources

Although recent laboratory simulations have demonstrated that organic matter prevents the degradation of polycyclic aromatic hydrocarbons (PAHs), their role in the long-range transport of PAHs in the real atmosphere remains poorly understood. In this study, we measured the chemical composition and mixing state of PAHs-containing individual particles in aerosols from three sources, one urban area and one remote area. PAHs-containing particles were classified into five types: organic carbon (OC), potassium mixed with organic carbon (KOC), potassium mixed with sodium (KNa), Krich and PAH-rich. The PAH-rich and KOC particles were the main types of particles produced by vehicle exhaust/coal burning and biomass burning, respectively, accounting for >50% of the PAHs-containing particles. It was found that organic matter enhancement of PAHs-containing particles occurs in the ambient atmosphere, with organic-rich (OC and KOC) particles accounting for >90%. Further analysis revealed that the increase in the fractions of PAHs was related to the mixing state with organic compounds due to the protection of organics against PAHs and/or the aging of PAHs-containing particles. The results of this study improve our understanding of the chemical composition and mixing state of PAHs particles in atmospheric aerosols from emission sources and urban and remote areas, and provide field observation evidence to support the promotion of the study of long-range transport of PAHs by organics.