Laboratory-generated Aerosols Research Articles

Study on quantitative generation technology of bio-fluorescence calibration particles based on inkjet generator

Accurate measurements are critical for timely early warning and effective prevention of epidemics due to the continuing impact of bioaerosols on human health. In recent years, researchers have been focused on developing and calibrating online monitoring instruments. However, there is still a lack of laboratory-generated standard aerosol samples suitable for calibration. Therefore, in this study, we utilized a self-developed Ink Jet Aerosol Generator (H-IJAG) to achieve controllable generation of monodisperse aerosol standard particles. The Aerosol Particle Size Spectrometer (APSS, TOPAS 323) was employed as the particle detector. The diameter of the droplet was calculated by measuring the projected area of the droplet in the same image using Image-J software. Experimental results demonstrated that under standardized inkjet parameters, H-IJAG exhibited good reliability and reproducibility, and generated solid particles within (0.4–15) μm. To better simulate the laser-induced fluorescence emission properties of ambient bioaerosol, tryptophan (Trp) and 7-hydroxycoumarin-4-acetic acid (7-HCA) were selected as solutes of the laboratory-generated aerosol samples, which are known bio-fluorescent materials. According to the law of propagation of uncertainty, the relative uncertainty of the volume equivalent diameter of Trp and 7-HCA solid particles by H-IJAG were 0.42 %, while the relative uncertainty of the particle number concentrations of Trp and 7-HCA solid particles generated by H-IJAG were 1.4 %. This optimized IJAG technique provides a promising solution for the accurate calibration of bioaerosol monitors.

Investigating the Applicability of a Global Average Calibration Line for Ambient Size-Resolved Cloud Condensation Nuclei (CCN) Measurements: A Technical Note

Abstract Aerosol–cloud–precipitation interaction represents the largest uncertainty in climate change’s current and future understanding. Therefore, aerosol properties affecting the cloud and precipitation formation and their accurate estimation is a first step in developing improved parameterizations for the prognostic climate models. Over the last couple of decades, a commercially available Cloud Condensation Nuclei Counter (CCNC) has been deployed in the field and laboratory for characterizing CCN properties of ambient or atmospherically relevant laboratory-generated aerosols. However, most of the CCN measurements performed in the field are often compounded with the erroneous estimation of CCN concentration and other parameters due to a lack of robust and accurate CCNC calibration. CCNC is not a plug-and-play instrument and requires prudent calibration and operation, to avoid erroneous data and added parameterization uncertainties. In this work, we propose and demonstrate the usability of a global calibration equation derived from CCNC calibration experiments from 8 contrasting global environments. Significant correlation was observed between the global calibration and each of the 16 individual experiments. A significant improvement in the correlation was observed when the calibration experiments were separated for high-altitude measurements. Using these equations, we further derived the effective hygroscopicity parameter and found lower relative uncertainty in the hygroscopicity parameter at higher effective supersaturation. Our results signify that altitude-based pressure change could be of importance for accurate calibration at high-altitude locations. Our results are consistent with previous studies emphasizing the criticality of the accurate CCN calibration for the lower supersaturations.

An Exhaled Breath Sampler Based on Condensational Growth and Cyclone Centrifugation (BSCC)

An exhaled breath sampler based on condensational growth and cyclone centrifugation (BSCC) was developed and evaluated. The BSCC increases the size of exhaled breath aerosols through condensational growth and then collects them as liquid sample via centrifugation. This enables rapid sample collection and eliminates certain pre-treatment steps for pathogenic microorganism analysis. Laboratory-generated aerosols were mixed with saturated water vapor to simulate exhaled breath, and the collection efficiency and the virus infectivity conservation efficiency of the BSCC were evaluated. The collection efficiency of the BSCC was approximately 66.7% for 100 nm aerosols and increased to nearly 100% for 3 µm aerosols. Besides, the BSCC maintained approximately 93.5% infectivity of atomized model virus aerosol (Pseudomonas bacteriophage Phi6). When collecting exhaled breath samples from nine volunteers, the average collection rate was 248.7 µL min–1. The BSCC achieved superior overall performance (i.e., 60% high collection efficiency and 40% higher infectivity conservation efficiency) compared with RTube, a commercial used exhaled breath sampler, indicating its potential for diagnosis of respiratory infection and measurements of exhaled viral aerosols.

Calibration and evaluation of a broad supersaturation scanning (BS2) cloud condensation nuclei counter for rapid measurement of particle hygroscopicity and cloud condensation nuclei (CCN) activity

Abstract. For understanding and assessing aerosol–cloud interactions and their impact on climate, reliable measurement data on aerosol particle hygroscopicity and cloud condensation nuclei (CCN) activity are required. The CCN activity of aerosol particles can be determined by scanning particle size and supersaturation (S) in CCN measurements. Compared to an existing differential mobility analyzer (DMA) with CCN activity measurement, a broad supersaturation scanning CCN (BS2-CCN) system, in which particles are exposed to a range of S simultaneously, can measure the CCN activity with a high time resolution. Based on a monotonic relation between the activation supersaturation of aerosol particles (Saerosol) and the activated fraction (Fact) of the BS2-CCN measurement, we can derive κ, a single hygroscopicity parameter, directly. Here, we describe how the BS2-CCN system can be effectively calibrated and which factors can affect the calibration curve (Fact−Saerosol). For calibration, size-resolved CCN measurements with ammonium sulfate and sodium chloride particles are performed under three different thermal gradient (dT) conditions (dT=6, 8, and 10 K). We point out key processes that can affect the calibration curve and thereby need to be considered as follows: first, the shape of the calibration curve is primarily influenced by Smax, the maximum S in the activation tube. We need to determine appropriate Smax depending on the particle size and κ to be investigated. To minimize the effect of multiply charged particles, a small geometric mean diameter (Dg) and geometric standard deviation (σg) in number size distribution are recommended when generating the calibration aerosols. Last, Fact is affected by particle number concentration and has a decreasing rate of 0.02 per 100 cm−3 due to the water consumption in the activation tube. For evaluating the BS2-CCN system, intercomparison experiments between typical DMA-CCN and BS2-CCN measurements were performed with a laboratory-generated aerosol mixture and ambient aerosols. Good agreement of κ values between DMA-CCN and BS2-CCN measurements for both experiments shows that the BS2-CCN system can measure CCN activity well compared to the existing measurement method and can measure a broad range of hygroscopicity distributions with a high time resolution (∼1 s vs. a few minutes for a standard CCN activity measurement). As the hygroscopicity can be used as a proxy for the chemical composition, our method can also serve as a complementary approach for fast and size-resolved detection and estimation of aerosol chemical composition.

Measurement report: Cloud condensation nuclei activity and its variation with organic oxidation level and volatility observed during an aerosol life cycle intensive operational period (ALC-IOP)

Abstract. Cloud condensation nuclei (CCN) spectrum and the CCN activated fraction of size-resolved aerosols (SR-CCN) were measured at a rural site on Long Island during the Department of Energy (DOE) aerosol life cycle intensive operational period (ALC-IOP) from 15 July to 15 August 2011. During the last week of the ALC-IOP, the dependence of the activated fraction on aerosol volatility was characterized by sampling downstream of a thermodenuder (TD) operated at temperatures up to 100 ∘C. Here we present aerosol properties, including aerosol total number concentration, CCN spectrum, and the CCN hygroscopicity, for air masses of representative origins during the ALC-IOP. The hygroscopicity of organic species in the aerosol is derived from CCN hygroscopicity and chemical composition. The dependence of organic hygroscopicity on the organic oxidation level (e.g., atomic O:C ratio) agrees well with theoretical predictions and results from previous laboratory and field studies. The derived κorg and O:C ratio first increase as TD temperature increases from 20 ∘C (i.e., ambient temperature) to 50 or 75 ∘C and then decrease as TD temperature further increases to 100 ∘C. The initial increases of O:C and κorg with TD temperature below 50 ∘C are likely due to evaporation of more volatile organics with relatively lower O:C and hygroscopicity such as primary organic aerosol. At the high TD temperatures, the decreases of O:C and κorg indicate that evaporated organics were more oxygenated and had lower molecular weights. These trends are different from previous laboratory experiments and field observations, which reported that organic O:C increased monotonically with increasing TD temperature, whereas κorg decreased with the TD temperature. One possible reason is that previous studies were either focused on laboratory-generated secondary organic aerosol (SOA) or based on field observations at locations more dominated by SOA.

Insights on the Working Principles of Secondary Electrospray Ionization High-Resolution Mass Spectrometry for Quantitative Analysis of Aerosol Chemical Composition

Real-time mass spectrometry (MS) has attracted increasing interest in environmental analysis due to its advantages in high time resolution, minimization of sampling artifact, and avoidance of time-consuming sample pretreatment. Among real-time MS methods, secondary electrospray ionization MS (SESI-MS) is showing great promise for the detection of organic compounds in atmospheric particulate matter. In this study, we demonstrated the working principles of secondary nanoelectrospray ionization (Sec-nESI) for real-time measurement of laboratory-generated organic aerosols using l-tartaric acid (TA) as a model compound. Factors affecting the detection of TA particles using a homemade Sec-nESI source coupled with a high-resolution mass spectrometer are systematically investigated. Temperature of ion transport capillary (ITC) was found to be the key factor in determining the ion signal intensity, which shows an increase of intensity by a factor of 100 from ITC temperature of 100–300 °C and could be attributed to more efficient desolvation and ionization. The characteristic fragment ion at m/z 72.99 was selected for quantitative analysis of TA at normalized collision energy of 50%, the optimal value applied during MS/MS analysis. Detection limit of 0.14 µg/m3 and a linear range of 0.2–2.97 µg/m3 are achieved. Satisfactory correlations between ion signal intensity and particle surface area (R2 = 0.969) and mass concentration (R2 = 0.967) were obtained. Although an equally good correlation was observed between signal intensity and particle surface area, the good correlation between signal intensity and particle mass concentration indicates that high solubility of TA ensures efficient dissolution of TA in the primary ESI droplets for further ionization.

New in situ aerosol hyperspectral optical measurements over 300–700 nm – Part 1: Spectral Aerosol Extinction (SpEx) instrument field validation during the KORUS-OC cruise

Abstract. In situ observations of spectrally resolved aerosol extinction coefficients (300–700 nm at ∼ 0.8 nm resolution) from the May–June 2016 Korea–United States Ocean Color (KORUS-OC) oceanographic field campaign are reported. Measurements were made with the custom-built Spectral Aerosol Extinction (SpEx) instrument that previously has been characterized only using laboratory-generated aerosols of known size and composition. Here, the performance of SpEx under realistic operating conditions in the field was assessed by comparison to extinction coefficients derived from commercial instruments that measured scattering and filter-based absorption coefficients at three discrete visible wavelengths. Good agreement was found between these two sets of extinction coefficients with slopes near unity for all three wavelengths within the SpEx measurement error (± 5 Mm−1). The meteorological conditions encountered during the cruise fostered diverse ambient aerosol populations with varying sizes and composition at concentrations spanning 2 orders of magnitude. The sampling inlet had a 50 % size cut of 1.3 µm diameter particles such that the in situ aerosol sampling suite deployed aboard ship measured fine-mode aerosols only. The extensive hyperspectral extinction data set acquired revealed that nearly all measured spectra exhibited curvature in logarithmic space, such that Ångström exponent (α) power law fits could lead to large errors compared to measured values. This problem was particularly acute for α values calculated over only visible wavelengths and then extrapolated to the UV, highlighting the need for measurements in this wavelength range. Second-order polynomial fits to the logarithmically transformed data provided a much better fit to the measured spectra than the linear fits of power laws. Building on previous studies that used total column aerosol optical depth observations to examine the information content of spectral curvature, the relationship between α and the second-order polynomial fit coefficients (a1 and a2) was found to depend on the wavelength range of the spectral measurement such that any given α maps into a line in (a1, a2) coefficient space with a slope of −2LN(λch), where λch is defined as the single wavelength that characterizes the wavelength range of the measured spectrum (i.e., the “characteristic wavelength”). Since the curvature coefficient values depend on λch, it must be taken into account when comparing values from spectra obtained from measurement techniques with different λch. Previously published work has shown that different bimodal size distributions of aerosols can exhibit the same α yet have differing spectral curvature with different (a1, a2). This implies that (a1, a2) contain more information about size distributions than α alone. Aerosol size distributions were not measured during KORUS-OC, and the data reported here were limited to the fine fraction, but the (a1, a2) maps obtained from the SpEx data set are consistent with the expectation that (a1, a2) may contain more information than α – a result that will be explored further with future SpEx and size distribution data sets.

Quantitative Performance Analysis of Respiratory Facemasks Using Atmospheric and Laboratory Generated Aerosols Following with Gamma Sterilization

ABSTRACT The emergence of the recent COVID-19 pandemic has rendered mandatory wearing of respiratory masks by infected persons, frontline workers, security personnel and members of the public. This has caused a sudden shift of focus, and significant demand on availability, effectiveness, reuse after sterilisation and development of facemask. Toward this, three types of masks viz. N95, non-woven fabric and double layer cotton cloth are being used by the majority of the population across the world as an essential inhalation protective measure for suppressing the entry of virus-laden respiratory droplets. The Filtering Efficiency (FE) of these masks are tested for atmospheric and laboratory-generated aerosols of size 1.0 µm and 102.7 nm particles before and after sterilisation and the two flow rate conditions corresponding to normal breath rate and during sneezing/coughing. Sterilisation is carried out using a gamma irradiator containing Co-60 source for the two-dose exposures viz. 15 kGy and 25 kGy. The FE of surgical and cloth masks is found to be in the range of 15.76 ± 0.22 to 22.48 ± 3.92%, 49.20 ± 8.44 to 60 ± 7.59% and 73.15 ± 3.73 to 90.36 ± 4.69% for aerosol sizes 0.3–5.0, 1.0–5.0 and 3.0–5.0 µm atmospheric aerosols respectively. The FE of cloth and surgical masks ranges from 45.07 ± 6.69% to 63.89 ± 4.44% and 56.58 ± 1.69% to 83.95 ± 1.04% for 1.0 µm laboratory-generated aerosol for two flow rate, control and irradiated conditions. The FE of N95 mask is found to be more than 95% for atmospheric aerosol, and 1.0 µm laboratory-generated aerosol. However, FE reduced to about 70% for most penetrating particle size after sterilisation. Further, FE reduced to 84% for the particle > 0.3 µm and to 87% for the particle < 0.3 µm after sterilisation. The reduction in FE for N95 mask after sterilization is associated with the reduction of electrostatic interaction of filter medium with particles laden in the air stream. Instead of disposing of N95 masks after a single use, they can be reused a few times as N70 mask during this pandemic crisis after sterilisation. The use of cotton cloth masks in the general public serves fit for the purpose than surgical masks.

Experimental Study on the Dependency of Ice Nucleation Active Surface Site Density on ATD Aerosol Size

In light of the percentage of Earth’s cloud coverage, heterogeneous ice nucleation in clouds is the most important global-scale pathway. More recent parameterizations of ice nucleation processes in the atmosphere are based on the concept of ice nucleation active surface site density (ns). It is usually assumed that ns is independent of time and aerosol size distribution, i.e. that the surface properties of aerosols of the same species do not vary with size. However, the independence of ns on aerosol size for every species has been questioned. This study presents the results of ice nucleation processes of ATD laboratory-generated aerosol (particle diameters of 0 - 3 μm). Ice nucleation in the condensation mode was performed in a Dynamic Filter Processing Cham- ber at temperatures of -18°C and -22°C, with a saturation ratio with respect to water of 1.02. Results show that ns increased by lowering the nucleation temperature, and was also dependent on the particle size. The ns of particles collected on the filters, after a 0.5 μm D50 cut-off cyclone, resulted statistically higher with respect to the values obtained from the particles collected on total filters. The results obtained suggest the need for further investigation of ns dependence of same composition aerosol particles with a view to support weather and climate predictions.

Effects of aerosol type and simulated aging on performance of low-cost PM sensors

Studies that characterize the performance of low-cost particulate matter (PM) sensors are needed to help practitioners understand the accuracy and precision of the mass and number concentrations reported by different models. We evaluated Plantower PMS5003, Sensirion SPS30, and Amphenol SM-UART-04L PM sensors in the laboratory by exposing them to: (1) four different polydisperse aerosols (ammonium sulfate, Arizona road dust, NIST Urban PM, and wood smoke) at concentrations ranging from 10 to 1000 μg m−3, (2) hygroscopic and hydrophobic aerosols (ammonium sulfate and oil) in an environment with varying relative humidity (15%–90%), (3) polystyrene latex spheres (PSL) ranging from 0.1 to 2.0 μm in diameter, and (4) extremely high concentrations of Arizona road dust (18-h mean total PM = 33,000 μg m−3; 18-h mean PM2.5 = 7300 μg m−3). Linear models relating PMS5003- and SPS30-reported PM2.5 concentrations to TEOM-reported ammonium sulfate concentrations up to 1025 μg m−3, nebulized Arizona road dust concentrations up to 540 μg m−3, and NIST Urban PM concentrations up to 330 μg m−3 had R2 ≥ 0.97; however, an F-test identified a significant lack of fit between the model and the data for each sensor/aerosol combination. Ratios of filter-derived to PMS5003-reported PM2.5 concentrations were 1.4, 1.7, 1.0, 0.4, and 4.3 for ammonium sulfate, nebulized Arizona road dust, NIST Urban PM, wood smoke, and oil mist, respectively. For SPS30 sensors, these ratios were 1.6, 2.1, 2.1, 0.6, and 2.2, respectively. Collocated PMS5003 sensors were less precise than collocated SPS30 sensors when measuring ammonium sulfate, nebulized Arizona road dust, NIST Urban PM, oil mist, or PSL. Our results indicated that particle count data reported by the PMS5003 were not reliable. The number size distribution reported by the PMS5003 (a) did not agree with APS data and (b) remained roughly constant whether the sensors were exposed to 0.1 μm PSL, 0.27 μm PSL, 0.72 μm PSL, 2.0 μm PSL, or any of the other laboratory-generated aerosols. The size distribution reported by the SPS30 did not always agree with APS data, but did shift towards larger particle sizes when the sensors were exposed to 0.72 PSL, 2.0 μm PSL, oil mist, or Arizona road dust from a fluidized bed generator. The proportions of PM mass assigned as PM1, PM2.5, and PM10 by all three sensor models shifted as the PSL size increased. After the sensors were exposed to high concentrations of Arizona road dust for 18 h, PM2.5 concentrations reported by SPS30 sensors remained consistent, whereas 3/8 PMS5003 sensors and 2/7 SM-UART-04L sensors began reporting erroneously high values.

Coupling an online ion conductivity measurement with the particle-into-liquid sampler: Evaluation and modeling using laboratory and field aerosol data.

A particle-into-liquid sampler (PILS) was coupled to a flow-through conductivity cell to provide a continuous, nondestructive, online measurement in support of offline ion chromatography analysis. The conductivity measurement provides a rapid assessment of the total ion concentration augmenting slower batch-sample data from offline analysis and is developed primarily to assist airborne measurements, where fast time-response is essential. A conductivity model was developed for measured ions and excellent closure was derived for laboratory-generated aerosols (97% conductivity explained, R2 > 0.99). The PILS-conductivity measurement was extensively tested throughout the NASA Cloud, Aerosol and Monsoon Processes: Philippines Experiment (CAMP2Ex) during nineteen research flights. A diverse range of ambient aerosol was sampled from biomass burning, fresh and aged urban pollution, and marine sources. Ambient aerosol did not exhibit the same degree of closure as the laboratory aerosol, with measured ions only accountable for 43% of the conductivity. The remaining fraction of the conductivity was examined in combination with ion charge balance and found to provide additional supporting information for diagnosing and modeling particle acidity. An urban plume case study was used to demonstrate the utility of the measurement for supplementing compositional data and augmenting the temporal capability of the PILS.

Evaluation of a high flow rate electrostatic precipitator (ESP) as a particulate matter (PM) collector for toxicity studies

In this study, we investigated the performance of an electrostatic precipitator (ESP) operating at high flow rates (i.e., 50–100 lpm) as a fine particulate matter (PM2.5) collector for toxicological studies. The ESP optimum configuration (i.e., flow rate of 75 lpm and applied voltage of +12 kV) was determined based on maximum particle collection efficiencies and minimum ozone emissions associated with the instrument using different laboratory-generated aerosols. This configuration resulted in particle collection efficiencies above 80% for almost all particles in the size range of 0.015–2.5 μm while the ozone concentration was 17 ppb. The ESP was then deployed to our sampling site in central Los Angeles to evaluate its performance using ambient particles under the optimum configuration. Chemical composition and oxidative potential of PM2.5 samples collected on the foils placed inside the ESP tube were compared with those collected concurrently on filters and aerosol slurries using the versatile aerosol concentration enrichment system (VACES) operating in parallel. Our results demonstrated that the ESP was more efficient in preserving labile inorganic ions and total organic carbon (TOC) compared to filters. PM samples collected on ESP substrates also showed higher intrinsic oxidative potential compared to the filters, which might be the result of better preservation of redox active semi-volatile organic compounds on the ESP substrates. However, the TOC concentrations and intrinsic oxidative potential of PM samples collected on ESP substrates were somewhat lower than the aerosol slurries collected by the VACES, probably due to deficiency of water-insoluble compounds in extracted PM samples from ESP substrates. In conclusion, while particle collection for toxicological purposes by the ESP is somewhat inferior to a direct aerosol-into-liquid collection, the ESP performs equally well, if not better, than conventional filter samplers and can be utilized as a simple and adequately efficient PM collector for toxicological studies.

Measurement of Light Absorbing Aerosols with Folded-Jamin Photothermal Interferometry.

In this study, a photothermal interferometer was developed, based on a folded-Jamin polarization instrument with refractive-index sensitive configuration, in order to characterize light-absorbing aerosols. The feasibility of our interferometric technique was demonstrated by performing photothermal spectroscopy characterizing spark-generated black carbon particles with atmospherically relevant concentrations and atmospheric aerosols in a metropolitan area. The sensitivity of this interferometric system for both laboratory-generated aerosols and atmospheric aerosols was ~ 1 (μg/m3)/μV, which is sufficient for the monitoring of black carbon aerosol in urban areas.

An aerosol concentrator/diffusion battery tandem to concentrate and separate ambient accumulation mode particles for evaluating their toxicological properties

We designed and evaluated the performance of a tandem technique, consisting of a previously developed versatile aerosol concentration enrichment system (VACES) combined with a compact screen-type diffusion battery that removes ambient ultrafine particles (UFP) from the airflow to enable us to conduct exposures directly on concentrated ambient accumulation mode (0.18–2.5 μm) particles. The performance of the diffusion battery was evaluated first under controlled conditions using NaCl laboratory-generated aerosols. Based on the laboratory tests, the optimum operational conditions of the diffusion battery were selected in terms of the flow rate (i.e., 5 lpm) and number of stages (i.e., 6). The diffusion battery was then deployed to our sampling site in central Los Angeles and connected to the VACES in order to evaluate the performance of the VACES/diffusion battery tandem using concentrated ambient particulate matter (PM2.5). Results of the field tests confirmed the ability of this tandem technique to concentrate effectively the accumulation mode PM with the majority of the ultrafine particles removed from the concentrated aerosol. The 50% cutpoint of the diffusion battery was at around 100 nm, while the removal efficiency exceeded 70–90% for particles smaller than 50 nm. Comparison of the mass concentrations and chemical composition of the accumulation mode PM collected using the tandem technique with those collected using a MOUDI sampler operating in parallel showed excellent overall agreement (within 5–15% variation), corroborating the effectiveness of the VACES/diffusion battery tandem technique for application in exposure studies to concentrated ambient accumulation mode PM.

Development of Aerosol-LIBS (Laser Induced Breakdown Spectroscopy) for Real-time Monitoring of Process-induced Particles

ABSTRACT Laser-induced breakdown spectroscopy (LIBS) has been increasingly used in recent years to rapidly detect the elemental compositions of various materials in different media (i.e., solids, liquids, and gases). In this study, an aerosol-LIBS system was developed for the real-time monitoring of process-induced particles generated during semiconductor manufacturing. The developed system consists primarily of a laser, a spectrometer, optics, and an aerosol chamber; the last element was constructed for the application of the aerosol-LIBS to various semiconductor manufacturing processes and comprises exhaust tubes and low pressure and high temperature chambers. The system was evaluated for its sensitivity to various elements using laboratory-generated aerosols and successfully detected P, Fe, Mg, Cu, Co, Ni, Ca, Na, and K emission lines. Further evaluation of the aerosol-LIBS is ongoing.

Collection of airborne bacteria and yeast through water-based condensational growth

One limitation in air sampling of airborne microorganisms is their inactivation by forceful impaction and/or dehydration during the collection process. Proper inhalation risk assessments require proof of viability, as non-viable microorganisms cannot cause infectious diseases. In this study, laboratory-generated aerosols of a vegetative bacterium (E. coli) or yeast (S. kudriavzevii) were collected by a laminar-flow water-based condensational “growth tube collector (GTC),” and the GTC’s collection efficiencies were compared with those using an industry standard BioSampler. Collection efficiencies resulting from two types of collection media, phosphate-buffered saline (PBS) and nutrient media (Nutrient Broth, NB, for E. coli, and Yeast Tryptone Glucose Broth, YTGB, for S. kudriavzevii) were also assessed. Both the GTC and the BioSampler performed equally when PBS was used as the collection medium for E. coli, whereas more viable E. coli cells were collected in the GTC than the BioSampler with NB. For S. kudriavzevii, the GTC outperformed the BioSampler using either PBS or YTGB. This is likely because aerosolized E. coli cells can better survive impaction than S. kudriavzevii under the conditions used, and the BioSampler has a much higher collection efficiency for particles in the size range of single-celled E. coli than S. kudriavzevii. Moreover, the GTC had a detection limit one order of magnitude lower for yeast aerosols compared with that of the BioSampler. These results indicate that the GTC is a promising device for sampling viable aerosolized gram-negative bacteria and yeast, as it is less damaging to these types of microorganisms during the collection process.

Development of laser-induced breakdown spectroscopy (LIBS) with timed ablation to improve detection efficiency

ABSTRACTA laser-induced breakdown spectrometer (LIBS) was developed for determining the elemental composition of individual airborne particles. The system employs two lasers focused on a narrow beam of particles. A continuous wave laser placed upstream scatters light from particles, while a pulse laser downstream ablates the particles. The scattered light from the upstream laser is used to trigger the downstream pulse laser, resulting in more accurate hitting of the particles than a free-firing laser system without the triggering signal (i.e., constant pulse laser firing). Various laboratory-generated aerosols (NaCl, MgCl2, KCl, and CaCl2) were used to evaluate the newly developed LIBS system. Particles were tightly focused into a center line with a sheath air focusing system using an optimum aerosol-to-sheath air velocity ratio. The locations of both the scattering laser and pulse laser beams were precisely controlled by a motorized X-Y stage controller. Data showed that for the LIBS with the triggering ...

Light-Absorbing Brown Carbon Aerosol Constituents from Combustion of Indonesian Peat and Biomass.

Light-absorbing brown carbon (BrC) constituents of organic aerosol (OA) have been shown to significantly absorb ultraviolet (UV) and visible light and thus impact radiative forcing. However, molecular identification of the BrC constituents is still limited. In this study, we characterize BrC constituents at the molecular level in (i) aerosols emitted by combustion of peat, fern/leaf, and charcoal from Indonesia and (ii) ambient aerosols collected in Singapore during the 2015 haze episode. Aerosols were analyzed using ultra performance liquid chromatography instrument interfaced to a diode array detector and electrospray ionization high-resolution quadrupole time-of-flight mass spectrometer operated in the negative ion mode. In the laboratory-generated aerosols, we identified 41 compounds that can potentially absorb near-UV and visible wavelengths, such as oxygenated-conjugated compounds, nitroaromatics, and S-containing compounds. The sum of BrC constituents in peat, fern/leaf, and charcoal burning aerosols are 16%, 35%, and 28% of the OA mass, respectively, giving an average contribution of 24%. On average, the BrC constituents account for 0.4% of the ambient OA mass; however, large uncertainties in mass closure remain because of the lack of authentic standards. This study highlights the potential of light-absorbing BrC OA constituents from peat, fern/leaf, and charcoal burning and their importance in the atmosphere.

Comparison of Oxidative Abilities of PM2.5 Collected at Traffic and Residential Sites in Japan. Contribution of Transition Metals and Primary and Secondary Aerosols

ABSTRACTFilter environmental samples of PM2.5 were collected at a traffic intersection in Kawasaki, Japan, and at a residential site (Tsukuba, Japan) in summer and winter, and the chemical compositions of the samples and their oxidative abilities in the dithiothreitol (DTT) assay were determined. Laboratory-generated aerosols (diesel exhaust particles [DEPs], gasoline direct injection spark ignition particles, and secondary organic aerosols [SOAs] generated from various precursors) were also investigated. To assess the effects of transition metals in the filter samples, we also conducted DTT assays on solutions of metal compounds similarly to the filter samples. In addition, the samples were pretreated with chelating reagents to mask the effects of transition metals. The DTT consumption average values for the filter samples collected at the traffic site were 53 and 50 pmol min–1 µg–1 in summer and winter, respectively, and these values were 1.3 and 1.1 times the corresponding values at the residential site and were also higher than the values for the laboratory-generated aerosols. Transition metals (Cu, Fe, Ni, and Mn) in the environmental samples were considered to be major contributors to DTT consumption (more than 80%). After removal of the effect of these transition metals with the chelating reagents, the oxidative abilities of the environmental samples were correlated with the amounts of organic carbon, water-soluble organic carbon, and organic acids and were weakly correlated with the amounts of elemental carbon and inorganic ions. We also found that the oxidative abilities based on the amount of organic carbon after removal of the effects of transition metals for DEPs, photochemically generated SOAs, and environmental samples except in the case of the traffic site in summer were compatible.

A broad supersaturation scanning (BS2) approach for rapid measurement of aerosol particle hygroscopicity and cloud condensation nuclei activity

Abstract. The activation and hygroscopicity of cloud condensation nuclei (CCN) are key to the understanding of aerosol–cloud interactions and their impact on climate. They can be measured by scanning the particle size and supersaturation in CCN measurements. The scanning of supersaturation is often time-consuming and limits the temporal resolution and performance of CCN measurements. Here we present a new approach, termed the broad supersaturation scanning (BS2) method, in which a range of supersaturation is simultaneously scanned, reducing the time interval between different supersaturation scans. The practical applicability of the BS2 approach is demonstrated with nano-CCN measurements of laboratory-generated aerosol particles. Model simulations show that the BS2 approach may also be applicable for measuring CCN activation of ambient mixed particles. Due to its fast response and technical simplicity, the BS2 approach may be well suited for aircraft and long-term measurements. Since hygroscopicity is closely related to the fraction of organics/inorganics in aerosol particles, a BS2-CCN counter can also serve as a complementary sensor for fast detection/estimation of aerosol chemical compositions.