Time-of-flight mass spectrometry methods for real time analysis of individual aerosol particles

A Novel Optical Instrument for Measuring Mass Concentration and Particle Size in Real Time

Particle mass and particulate size are two important parameters used to characterize the aerosol. Currently, there are a few methods for measuring particle mass concentration and particle size. However, the existing methods have their own shortcomings. In this article, we describe a novel laser scattering instrument that measures mass concentration and particle size in real time over a wide concentration range. This instrument combines laser scattering and time-of-flight aerodynamics in one optical device. There are two innovations in this paper: (1) Two APD detectors are used to receive scattered light. One receives forward-scattered light and the other receives side-scattered light. The advantage is that the sensitivity of the detector is increased greatly, and the ratio of forward and side scattering is used to further obtain the size and shape information of the particles. (2) In order to measure the high concentrations of aerosol, a high-speed ADC and FPGA is combined to achieve an anti-overlap algorithm objective. It has been verified by experiments that the anti-overlapping algorithm can effectively improve the applicability of the aerodynamic particle size spectrometer under high concentration conditions.

Highly time-resolved aerosol characteristics during springtime in Weizhou Island

A single particle aerosol mass spectrometer was deployed to measure the changes of single particle species and sizes during March 2015 in Weizhou Island of the Beibu Gulf, Guangxi province, South China. In this campaign, a total of 3,100,597 particles were sized, and 25.8% particles with both positive and negative mass spectrum were collected and 24.8% characterized in combination with the ART-2a neural network algorithm. The distribution of sized particles was mainly in from 520 to 600nm, and the diameters ranging from 340 to 1000nm accounted for above 90%. Eight types of particles were classified: Elemental Carbon containing (EC), Organic Carbon containing (OC), EC and OC combined containing particles, Na containing particles, K containing particles (K), Levoglucosan containing particles, mineral containing particles, and Heavy Metal containing particles (HM). EC, OC and K were the major containing particles, which accounted for 84.3% in the eight types particles. The relative ratio and size distribution of the three types were EC (48.1%, 620nm), OC (12.7%, 440nm), and K (23.5%, 600nm), respectively. The three types of particles were a bit increasing ratios compared with those in clean periods during haze pollution periods. Combined with the back-trajectory results from the Hysplit-4 model and local pollution sources revealed that the ambient air quality on the Weizhou Island may be influenced by biomass burning in the Indochina Peninsula (biomass burning in the Indochina Peninsula) from the transportation on higher level atmospheric layer and by mainland of south China located northeast of Weizhou Island on the ground.

Characteristics of atmospheric single particles during haze periods in a typical urban area of Beijing: A case study in October, 2014

To investigate the composition and possible sources of particles, especially during heavy haze pollution, a single particle aerosol mass spectrometer (SPAMS) was deployed to measure the changes of single particle species and sizes during October of 2014, in Beijing. A total of 2,871,431 particles with both positive and negative spectra were collected and characterized in combination with the adaptive resonance theory neural network algorithm (ART-2a). Eight types of particles were classified: dust particles (dust, 8.1%), elemental carbon (EC, 29.0%), organic carbon (OC, 18.0%), EC and OC combined particles (ECOC, 9.5%), Na-K containing particles (NaK, 7.9%), K-containing particles (K, 21.8%), organic nitrogen and potassium containing particles (KCN, 2.3%), and metal-containing particles (metal, 3.6%). Three haze pollution events (P1, P2, P3) and one clean period (clean) were analyzed, based on the mass and number concentration of PM2.5 and the back trajectory results from the hybrid single particle Lagrangian integrated trajectory model (Hysplit-4 model). Results showed that EC, OC and K were the major components of single particles during the three haze pollution periods, which showed clearly increased ratios compared with those in the clean period. Results from the mixing state of secondary species of different types of particles showed that sulfate and nitrate were more readily mixed with carbon-containing particles during haze pollution episodes than in clean periods.

Microorganism characterization by single particle mass spectrometry

In recent years a major effort by several groups has been undertaken to identify bacteria by mass spectrometry at the single cell level. The intent of this review is to highlight the recent progress made in the application of single particle mass spectrometry to the analysis of microorganisms. A large portion of the review highlights improvements in the ionization and mass analysis of bio-aerosols, or particles that contain biologically relevant molecules such as peptides or proteins. While these are not direct applications to bacteria, the results have been central to a progression toward single cell mass spectrometry. Developments in single particle matrix-assisted laser desorption/ionization (MALDI) are summarized. Recent applications of aerosol laser desorption/ionization (LDI) to the analysis of single microorganisms are highlighted. Successful applications of off-line and on-the-fly aerosol MALDI to microorganism detection are discussed. Limitations to current approaches and necessary future achievements are also addressed.

Laser-induced breakdown spectroscopy for ambient air particulate monitoring: correlation of total and speciated aerosol particle counts

A statistical analysis of ambient air particle monitoring, namely PM2.5, is presented to elucidate the correlations between laser-induced breakdown spectroscopy (LIBS)-based speciated aerosol monitoring and non-speciated aerosol monitoring (i.e., total particle counts). LIBS was used in a real-time, conditional-processing mode to identify individual aerosol particles containing detectable quantities of either calcium or sodium, as based on the resulting atomic emission signals. Using this technique, real-time measurements of speciated aerosol particle concentrations and analyte mass concentrations were evaluated for a total of 60 1-hour sampling periods spread over a 5-week period. For each 1-hour sampling period, total aerosol counts were simultaneously monitored using a commercial light scattering-based instrument. Over the 30 sampling periods, aerosol counts (both total and LIBS-based) were found to vary by more than one order of magnitude. For aerosol particles in the 500 nm to 2.5 microm size range, significant correlations were found between the two sampling methods, resulting in correlation coefficients (r2) ranging from 0.22 to 0.93. In addition, transient fluctuations in aerosol counts on a timescale of 5 to 10 minutes were successfully observed simultaneously with the two monitoring techniques, thereby demonstrating the temporal resolution of LIBS.

An overview of analytical applications of time of flight-mass spectrometric (TOF-MS) analyzers and an inductively coupled plasma-TOF-MS technique

A brief overview of the applications of time-of-flight mass spectrometry (TOF-MS) for analytical purposes is presented. The performance of TOF-MS combined with an inductively coupled plasma (ICP) ion source is discussed in detail. The advantages of TOF-MS detectors over the quadrupole mass filters for multi-elemental analysis of fast transient signals are discussed. The applications of ICP-TOF-MS for the detection of signals from laser ablation, electrothermal vaporization, gas and liquid chromatography, capillary electrophoresis and flow-injection analysis are reviewed.

Real-time single particle mass spectrometry: a historical review of a quarter century of the chemical analysis of aerosols

Real-time single particle mass spectrometry, or continuous aerosol mass spectrometry, was originally developed in the 1970s for the purpose of identifying the chemical composition of airborne particulate matter in real-time. Although this technique has continued to evolve throughout the following decades, the fundamental characteristic of this method remains the same, involving the continuous introduction of solid particle or liquid droplets directly into the ion source region of a mass spectrometer. Continuous sample introduction allows for the chemical analysis of single airborne particles in real-time. A number of mass analyzers have been employed in real-time single particle mass spectrometry. The original real-time single particle mass spectrometer used a magnetic sector mass analyzer. Quadrupole, double-focusing, and ion trap mass spectrometers have also been utilized. The majority of the current real-time single particle mass spectrometry techniques use time-of-flight mass spectrometry. In the literature, a variety of general names have been applied to real-time single particle mass spectrometry methods. These names include direct-inlet mass spectrometry, on-line laser microprobe mass spectrometry, particle analysis by mass spectrometry, particle beam mass spectrometry, and rapid-single particle mass spectrometry. This review covers real-time single particle mass spectrometry techniques that were developed from 1973 through 1998, specifically for analyzing airborne particulate matter, including environmental aerosols, biological aerosols, and clean-room aerosols. Because the majority of the historical and current real-time single particle mass spectrometers have been employed for atmospheric aerosols, this topic is the primary focus of this review. This review does not include on-line mass spectrometry methods that are employed as a detector for other instrumental methods, such as liquid chromatography.