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

The real-time detection of the mixing states of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs in ambient particles is of great significance for analyzing the source, aging process, and health effects of PAHs and nitro-PAHs; yet there is still few effective technology to achieve this type of detection. In this study, 11 types of PAH and nitro-PAH standard samples were analyzed using a high performance-single particle aerosol mass spectrometer (HP-SPAMS) in lab studies. The identification principles ‘parent ions’ and ‘mass-to-charge (m/z) = 77’ of each compound were obtained in this study. It was found that different laser energies did not affect the identification of the parent ions. The comparative experiments of ambient atmospheric particles, cooking and biomass burning emitted particles with and without the addition of PAHs were conducted and ruled out the interferences from primary and secondary organics on the identification of PAHs. Besides, the reliability of the characteristic ions extraction method was evaluated through the comparative study of similarity algorithm and deep learning algorithm. In addition, the real PAH-containing particles from vehicle exhaust emissions and ambient particles were also analyzed. This study improves the ability of single particle mass spectrometry technology to detect PAHs and nitro-PAHs, and HP-SPAMS was superior to SPAMS for detecting single particles containing PAHs and nitro-PAHs. This study provides support for subsequent ambient observations to identify the characteristic spectrum of single particles containing PAHs and nitro-PAHs.     

Biomass chemical looping gasification for syngas production using modified hematite as oxygen carriers

Syngas is a clean energy carrier and a major industrial feedstock. In this paper, syngas was produced via biomass chemical looping gasification(CLG) process. Hematite, the most common Fe-based oxygen carrier(OC), was modified with different metal oxides(CeO₂, CaO and MgO) by the impregnation method. The hematite modified by CeO₂, CaO and MgO was namely as CeO₂-hematite(CeO₂-H), CaO-hematite(CaO-H) and MgO-hematite(MgO-H), respectively. The introduction...     

Characterization of a new smog chamber for evaluating SAPRC gas-phase chemical mechanism

A new state-of-the-art indoor smog chamber facility(CAPS-ZJU) has been constructed and characterized at Zhejiang University,which is designed for chemical mechanism evaluation under well-controlled conditions.A series of characterization experiments were performed to validate the well-established experimental protocols,including temperature variation pattern,light spectrum and equivalent intensity(J_NO2),injection and mixing performance,as well as gases and particle wall loss.In additi...     

An integrated chemical mass balance and source emission inventory model for the source apportionment of PM2.5 in typical coastal areas

The source apportionment of PM_2.5 is essential for pollution prevention.In view of the weaknesses of individual models,we proposed an integrated chemical mass balancesource emission inventory(CMB-SEI) model to acquire more accurate results.First,the SEI of secondary component precursors(SO₂,NO_x,NH₃,and VOCs) was compiled to acquire the emission ratios of these sources for the precursors.Then,a regular CMB simulation was executed to obtain the contribut...     

Surface-enhanced Raman scattering for mixing state characterization of individual fine particles during a haze episode in Beijing, China

The nondestructive characterization of the mixing state of individual fine particles using the traditional single particle analysis technique remains a challenge. In this study, fine particles were collected during haze events under different pollution levels from September 5 to 11 2017 in Beijing, China. A nondestructive surface-enhanced Raman scattering (SERS) technique was employed to investigate the morphology, chemical composition, and mixing state of the multiple components in the individual fine particles. Optical image and SERS spectral analysis results show that soot existing in the form of opaque material was predominant during clear periods (PM_2.5 ≤ 75 µg/m³). During polluted periods (PM_2.5 > 75 µg/m³), opaque particles mixed with transparent particles (nitrates and sulfates) were generally observed. Direct classical least squares analysis further identified the relative abundances of the three major components of the single particles: soot (69.18%), nitrates (28.71%), and sulfates (2.11%). A negative correlation was observed between the abundance of soot and the mass concentration of PM_2.5. Furthermore, mapping analysis revealed that on hazy days, PM_2.5 existed as a core-shell structure with soot surrounded by nitrates and sulfates. This mixing state analysis method for individual PM_2.5 particles provides information regarding chemical composition and haze formation mechanisms, and has the potential to facilitate the formulation of haze prevention and control policies.     

Protonated acetone ion chemical ionization time-of-flight mass spectrometry for real-time measurement of atmospheric ammonia

Ammonia (NH₃) is ubiquitous in the atmosphere, it can affect the formation of secondary aerosols and particulate matter, and cause soil eutrophication through sedimentation. Currently, the use of radioactive primary reagent ion source and the humidity interference on the sensitivity and stability are the two major issues faced by chemical ionization mass spectrometer (CIMS) in the analysis of atmospheric ammonia. In this work, a vacuum ultraviolet (VUV) Kr lamp was used to replace the radioactive source, and acetone was ionized under atmospheric pressure to obtain protonated acetone reagent ions to ionize ammonia. The ionization source is designed as a separated three-zone structure, and even 90 vol.% high-humidity samples can still be directly analyzed with a sensitivity of sub-ppbv. A signal normalization processing method was designed, and with this new method, the quantitative relative standard deviation (RSD) of the instrument was decreased from 17.5% to 9.1%, and the coefficient of determination was increased from 0.8340 to 0.9856. The humidity correction parameters of the instrument were calculated from different humidity, and the ammonia concentrations obtained under different humidity were converted to its concentration under zero humidity condition with these correction parameters. The analytical time for a single sample is only 60 sec, and the limit of detection (LOD) was 8.59 pptv (signal-to-noise ratio S/N = 3). The ambient measurement made in Qingdao, China, in January 2021 with this newly designed CIMS, showed that the concentration of ammonia ranged from 1 to 130 ppbv.     

Synthesis of hierarchical porous carbon with high surface area by chemical activation of(NH4)2C2O4 modified hydrochar for chlorobenzene adsorption

In this work,hydrothermal technique combined with KOH activation were employed to develop a series of porous carbons (NPCK-x) using tobacco stem as a low-cost carbon source and (NH₄)₂C₂O₄ as a novel nitrogen-doping agent.Physicochemical properties of NPCK-x were characterized by Brunauer-Emmett-Teller,field emission scanning electron microscopy,X-ray diffraction,Raman microscope,elemental analysis,and X-ray photoelectron spectroscopy.Results showed tha...