The Los Angeles Aerosol Characterization and Source Apportionment Study: An Overview

The Los Angeles Aerosol Characterization and Source Apportionment Study (LA-ACSAS) is a decade-long laboratory and field study undertaken by the Southern California Edison Company (SCE) to characterize the chemical composition of fine (d _p < 3.5 μm) particles, PM_3,5, in the Los Angeles Basin, in terms of sulfate, nitrate, organic compounds and trace metals and apportion their sources. This paper provides an overview of the study results and summarizes the important conclusions regarding the composition and sources of PMJS in the Los Angeles Basin, especially regarding the organic fraction.     

Design and Characterization of a Fluidized Bed Aerosol Generator: A Source for Dry,Submicrometer Aerosol

A fluidized bed aerosol generator has been designed and built for the purpose of generating a constant output of dry, submicrometer particles with a large number density. The output of the fluidized bed for generating aerosol particles from dry soot powder has been characterized using a differential mobility analyzer and a condensation particle counter. The particle size distribution is bimodal, with a mode in the submicrometer diameter size range and a mode in the supermicrometer diameter size range. The larger diameter mode is fully separated from the smaller mode and can thus be easily removed from the aerosol flow using impaction techniques. The distribution in the submicrometer size range is nearly log-normal, with a count median diameter falling between 0.1 and 0.3 micrometers. A number density of greater than 10⁵ particles cm^-3 of soot particles in the submicrometer range can be produced, constant to within 25% (1 standard deviation) over a 4 h time period. The number density of particles produced in the submicrometer range was found to vary with the ratio of soot to bronze beads in the bed mixture, whether or not a feed system was used, and nitrogen flow rate through the fluidized bed and feed system.     

Side-by-Side Comparison of Four Techniques Explains the Apparent Differences in the Organic Composition of Generated and Ambient Marine Aerosol Particles

Copyright 2014 American Association for Aerosol Research     

Aerosol Charge Fractions Downstream of Six Bipolar Chargers: Effects of Ion Source,Source Activity,and Flowrate

Bipolar diffusion charging is used routinely in aerosol electrical mobility size distribution measurements. In this study, aerosol charge fractions produced by six bipolar chargers (neutralizers) were measured using a tandem differential mobility analyzer system. Factors that were studied include the type of ion source (²¹⁰Po, ⁸⁵Kr, ²⁴¹Am, and soft X-ray), source activity, charger design, and aerosol flowrate. It was found that all six types of neutralizers achieve stationary state charge distributions when the source activity is sufficiently high. For ²¹⁰Po neutralizers with an initial radioactivity of 18.5 MBq (0.5 mCi), stationary state charge distributions are achieved when the source is less than 3.25 years old (residual activity no less than 0.0527 MBq). Stationary state was achieved for ⁸⁵Kr neutralizers having residual radioactivity greater than 70 MBq. Source activities of ²⁴¹Am and soft X-ray neutralizers are discussed. Aerosol charge fractions for six neutralizers remain reasonably invariant over a wide range of flowrates. The positive charge fractions achieved by the soft X-ray neutralizer are higher than those by the other five neutralizers using radioactive sources while negative charge fractions for all neutralizers studied are all in a similar range. This study also raises questions about bipolar charging fractions used for data inversion in some scanning mobility particle spectrometer (SMPS) systems, and underscores the need to better understand bipolar charging to achieve more accurate measurements of particle size distributions.

Copyright 2014 American Association for Aerosol Research     

二次有机气溶胶中二羰基化合物的研究进展

二次有机气溶胶的形成是大气环境化学的研究热点。二羰基化合物对二次有机气溶胶形成具有重要的研究意义。由于二羰基化合物在液相中发生聚合反应,在液相中的分配大于Henry定律的预测值,影响二次有机气溶胶的形成。通过二羰基化合物乙二醛和甲基乙二醛在大气中光氧化和异相反应的研究,评述了二羰基化合物对二次有机气溶胶形成的研究发展。     

二次有机气溶胶的特征和形成机制

二次有机气溶胶(SOA)的形成是当今大气化学过程的研究热点之一. 城市大气中二次有机碳占颗粒物总有机碳的17%~65%. 单萜烯和芳香族化合物分别是SOA最重要的天然和人为源前体物,在大气中与×OH, NO3-和O3等氧化剂发生多途径反应形成有机酸、多官能团羰基化合物、硝基化合物等半挥发性有机物,通过吸附、吸收等过程进入颗粒相,改变了气溶胶的特性及其环境效应. 有机化合物表现出较强的源特征性,可以作为示踪分子解析颗粒物来源,二元羧酸是SOA的潜在示踪物. 论述了SOA研究的最新进展并指出了未来的研究方向.     

Impact of Fe Content in Laboratory-Produced Soot Aerosol on its Composition,Structure, and Thermo-Chemical Properties

Soot aerosol, which is a major pollutant in the atmosphere of urban areas, often contains not only carbonaceous matter but also inorganic material. These species, for example, iron compounds, originated from impurities in fuel or lubricating oil, additives or engine wear may change the physico-chemical characteristics of soot and hence its environmental impact. We studied the change of composition, structure, and oxidation reactivity of laboratory-produced soot aerosol with varying iron content. Soot types of various iron contents were generated in a propane/air diffusion flame by adjusting the doping amount of iron pentacarbonyl Fe(CO)₅ to the flame. Scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) was combined with cluster analysis (CA) to separate individual particles into definable groups of similar chemical composition representing the particle types in dependence of the iron content in soot. Raman microspectroscopy (RM) and infrared spectroscopy were applied for the characterization of the graphitic soot structure, hydrocarbons, and iron species. For the analysis of soot reactivity, temperature-programmed oxidation (TPO) was used. It is demonstrated that iron is most dominantly present in the form of amorphous Fe (III) oxide crystallizing to hematite α-Fe₂O₃ upon thermal treatment. Iron contaminations do not change the soot microstructure crucially, but Fe(CO)₅ doping of the flame impacts hydrocarbon composition. Soot oxidation reactivity strongly depends on the iron content, as the temperature of maximum carbon (di)oxide emission T _max follows an exponential decay with increasing iron content in soot. Based on the results of the thermo-chemical characterization of laboratory-produced internally mixed iron-containing soot, we can conclude that iron-containing combustion aerosol samples cannot be characterized unambiguously by current thermo-optical analysis protocols.

Copyright 2012 American Association for Aerosol Research     

The Thermal-Stability of Oligomers in Alpha-Pinene Secondary Organic Aerosol

Recent studies characterizing laboratory generated secondary organic aerosol (SOA) have shown that 50% or more of the particle mass is made up of oligomeric species, which based on molecular weight and structure should be nonvolatile. On the other hand, about 75% the particle mass is lost when SOA is passed through a denuder heated to 100°C, suggesting that it is semi-volatile. To study the reason for this discrepancy, the chemical effects of a thermal denuder (TD) on oligomers in laboratory SOA formed by ozonolysis of α-pinene were examined with high-resolution molecular mass spectrometry. Both monomers and oligomers in the particle phase were lost to the gas phase upon heating to 100°C. Additionally, when the species released to the gas phase during heating were allowed to readsorb onto the remaining particle mass, almost all of the readsorbed material was monomeric. Both of these observations suggest that oligomers decompose when heated in a TD. Chemical analysis of the remaining particle mass after passing through the TD showed formation of many new compounds that corresponded to oligomer decomposition products. While similar experiments should be performed with other aerosol types, these results suggest that care must be taken when attempting to use a TD at an elevated temperature to infer the volatility of SOA at ambient temperature.

Copyright 2012 American Association for Aerosol Research     

气溶胶单粒子成分和粒径的实时测量

利用气溶胶飞行时间激光质谱仪测定了两种芳香烃气溶胶的质谱,发现芳香族化合物产生的气溶胶粒子容易形成分子离子峰,对苯二酚还发生分子离子反应.对室内外空气中的气溶胶粒子的粒径进行实时检测的结果表明,室内外空气中的气溶胶粒子多以细粒子为主.实验结果表明,该仪器在大气气溶胶污染监测及相关研究领域具有重要的实用价值.     

灭火气溶胶发生剂灭火机理及配方设计

通过研究烟雾灭火剂与干粉灭火剂，探讨了灭火气溶胶发生剂的主要组分的选择原则,论述了灭火气溶胶发生剂的灭火机理,并由正交试验确定了发生剂的基本配方,试验证明灭火效果符合要求。     

Occurrence and Source Apportionment of Polycyclic Aromatic Hydrocarbons in Urban Residential Soils from National Capital Region,Uttar Pradesh,India

This study aims to investigate the level of priority polycyclic aromatic hydrocarbons (PAHs) and identification of their potential sources in residential soils. During the study, a total 36 soil samples collected from twelve residential locations at Sahibabad-Ghaziabad area of western Uttar Pradesh, India, a constituted part of the National Capital Region of India. Samples extracted using ultrasonication, cleaned with silica and analyzed by diode array detector–high-performance liquid chromatography using acetonitrile/water as mobile phase. The 25th and 75th percentile concentration of ∑PAHs was 264 μg kg^?1 and 584 μg kg^?1, respectively, with mean and median of 445 μg kg^?1 and 421 μg kg^?1. The detection frequency of PAHs in all samples was lower for low molecular weight PAHs (19%) than high molecular weight PAHs (81%). The concentration of seven probable carcinogenic PAHs accounted for 67% of the ∑PAHs. PAHs toxicity potential as benzo(a)pyrene toxicity equivalent ranged between 2.52–253 μg BaP_TEQ kg^?1. Composition profile of PAHs with different aromatic rings and selected diagnostic molecular ratios suggested the local pyrogenic sources of PAHs from vehicular emissions, diesel engines, biomass combustion, gasoline, and coal combustions.     

An In-Situ Instrument for Speciated Organic Composition of Atmospheric Aerosols: Thermal Desorption Aerosol GC/MS-FID (TAG)

We introduce a new in-situ instrument, Thermal desorption Aerosol GC/MS-FID (TAG), capable of hourly measurements of speciated organic compounds in atmospheric aerosols. Aerosol samples are collected into a thermal desorption cell by means of humidification and inertial impaction. The sample is thermally desorbed and transferred with helium carrier gas into a gas chromatography (GC) column, with subsequent detection by both quadrupole mass spectrometer (MS) and a flame ionization detector (FID). The collection and analysis steps are automated, yielding around the clock speciation. This approach builds on the extensive body of knowledge available for quantification and source apportionment of organic aerosols from past research using filter-based GC/MS analyses, but it is the first instrument to achieve in-situ time resolved measurements for an essentially unlimited number of samples, making it possible to analyze changes in organic aerosol speciation over timescales ranging from hours to seasons.     

Phase State and Deliquescence Hysteresis of Ammonium-Sulfate-Seeded Secondary Organic Aerosol

The phase state of secondary organic aerosol (SOA) has an impact on its lifetime, composition, and its interaction with water. To better understand the effect of phase state of SOA on climate interactions, we studied the SOA phase state and the effect of its history and report here the phase state and the humidity-induced phase hysteresis of multicomponent-seeded SOA particles produced in a large, continuously stirred tank reactor. We determined the phase state of the particles by their bounced fraction impacting on a smooth substrate in a low-pressure impactor. The particles were composed of ammonium sulfate ([NH₄]₂SO₄) seed and a secondary organic matter (SOM) shell formed from oxidized α-pinene or isoprene. The ammonium sulfate (AS) seed dominated the deliquescence of the α-pinene SOM multicomponent particles, whereas their efflorescence was strongly attenuated by the SOM coating. Particles coated with isoprene SOM showed continuous phase transitions with a lesser effect by the AS seed. The results agree with and independently corroborate contemporary research.

Copyright 2015 American Association for Aerosol Research     

Source Apportionment of Individual Carbonaceous Particles Using 14C and Laser Microprobe Mass Spectrometry

An exploratory study of laser microprobe mass spectra of individual atmospheric soot particles has been made in search of a potential combustion source tracer index. A tentative “cluster ratio index” (CRI = C₄ ^?/C₂ ^?) has been found and compared with bulk measurements of ¹⁴C in a set of ambient samples exhibiting varying impacts from woodburning and motor vehicle exhaust. A CRI-¹⁴C calibration curve resulted, and it led to the conclusion that, at the present level of precision, three particles (or agglomerates) of micrometer size or about 3 pg of carbon would be required for discrimination between the two pure sources. Mixture samples, such as those reported here, would require about 40 times as much. Classification of small set of individual particles from the mixed source ambient samples, suggests preservation of carbonaceous source identity at the single particle level.     

抚顺市大气颗粒物的研究进展

对近十年抚顺市PM10、PM2.5污染特征的研究结果进行总结,为了进一步全面研究PM2.5确定主要的污染源、各污染源的特征元素、PM2.5的样品成分。总结表明土壤尘、煤烟尘、尾气尘、工业尘、道路尘、有机碳是主要污染源,工业区、交通区、居民区和商业区是理想的采样点区域,理想的采样时间是按季节采样。     

Aerosol Concentrations During the 1999 Fresno Exposure Studies as Functions of Size,Season, and Meterology

Two 1999 Fresno exposure studies took place in February (winter season) and April/May (spring season) for periods of four weeks each. During that time, nearly continuous measurements of outdoor aerosol concentrations were made with a TSI Scanning Mobility Particle Sizer (SMPS) and a PMS optical particle counter (LASX). These instruments provide particle size distribution information from about 0.01 to 3     

Organic Aerosol Speciation: Intercomparison of Thermal Desorption Aerosol GC/MS (TAG) and Filter-Based Techniques

We compared measurements of organic molecular markers made using a novel Thermal Desorption Aerosol Gas Chromatograph/Mass Spectrometer (TAG) with two offline filter-based methods: solvent extraction GC/MS (SE-GC/MS) and thermal desorption GC/MS (TD-GC/MS). TAG is designed for automated, high time-resolved measurements of organic aerosol speciation. Laboratory and field measurements were performed to compare TAG and filter performance for n-alkanes, n-alkanoic acids, cholesterol, PAHs, and hopanes. Laboratory measurements of model organic aerosol mixtures of known composition were made in the Carnegie Mellon University smog chamber, and field measurements were made in downtown Pittsburgh. There was excellent agreement between techniques for hopanes and several PAHs, which are important markers for motor vehicle emissions. Agreement was also strong for moderately polar and nonpolar species in the high-concentration smog chamber experiments. Poorer agreement between filter and TAG observations was obtained for n-alkanes in ambient measurements. To further investigate the differences in n-alkane performance between these methods, potential matrix effects and internal consistency within the TAG and filter ambient air data sets were examined. We spiked a subset of ambient TAG samples with deuterated internal standards to examine potential matrix effects. Under typical conditions, there was little bias in recovery of deuterated standards. At extreme ambient aerosol levels, however, there were large biases in relative recovery, indicating matrix effects may be important under those conditions. Similar results were observed in laboratory experiments with engine lubricating oil. Applying internal standards in the TAG system would help track and correct for matrix effects influencing compound recovery.     

Quantification of Carboxylic and Carbonyl Functional Groups in Organic Aerosol Infrared Absorbance Spectra

Atmospheric aerosols are one of the least understood components of the climate system and incur adverse health effects on susceptible populations. Organic aerosols can make up as much as 80% of atmospheric aerosols (Lim and Turpin 2002 Lim, H. J. and Turpin, B. J. 2002. Origins of Primary and Secondary Organic Aerosol in Atlanta: Results’ of Time-Resolved Measurements During the Atlanta supersite experiment. Environ. Sci. Technol., 36: 4489–4496. 10.1021/es0206487[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]), and so its quantification and characterization plays an important role in reducing our uncertainty with regards to aerosol impacts on health and climate. As the number of organic molecules in the atmosphere are diverse in number (Hamilton et al. 2004 Hamilton, J. F., Webb, P. J., Lewis, A. C., Hopkins, J. R., Smith, S. and Davy, P. 2004. Partially Oxidised Organic Components in Urban Aerosol using GCXGC-TOF/MS. Atmos. Chem. Phys., 4: 1279–1290. [Crossref], [Web of Science ®] , [Google Scholar]), we advance a functional group representation of organic molecules as measured by Fourier transform infrared spectroscopy (FTIR) to characterize the chemical composition of particle samples. This study describes and evaluates the algorithm introduced by Russell et al. (2009 Russell, L. M., Takahama, S., Liu, S., Hawkins, L. N., Covert, D. S.Quinn, P. K. 2009. Oxygenated Fraction and Mass of Organic Aerosol from Direct Emission and Atmospheric Processing Measured on the R/V Ronald Brown During TEXAQS/GoMACCS 2006. J. Geophys. Res.-Atmos., 114: D00F05 10.1029/2008JD011275[Crossref], [Web of Science ®] , [Google Scholar]) for apportionment and quantification of oxygenated (carbonyl and hydroxyl) functional groups from infrared absorption spectra. Molar absorptivities for carbonyl and hydroxyl bonds in carboxylic groups are obtained for several dicarboxylic compounds, and applied to a multifunctional compound and mixture to demonstrate the applicability of this method for more complex samples. Furthermore, functional group abundances of two aldehydic compounds, 2-deoxy-d-ribose and glyceraldehyde, atomized from aqueous solution are in quantitative agreement with number of bonds predicted after transformation of these compounds into diols. The procedure for spectra interpretation and quantitative analysis is described through the context of an algorithm in which contributions of background and analyte absorption to the infrared spectrum are apportioned by the superposition of lineshapes constrained by laboratory measurements.

Copyright 2013 American Association for Aerosol Research