Fluorescent Aerosol Particles Research Articles

Assessing Characteristics and Variability of Fluorescent Aerosol Particles: Comparison of Two Case Studies in Southeastern Italy Using a Wideband Integrated Bioaerosol Sensor

Assessing Characteristics and Variability of Fluorescent Aerosol Particles: Comparison of Two Case Studies in Southeastern Italy Using a Wideband Integrated Bioaerosol Sensor

Roles of marine biota in the formation of atmospheric bioaerosols, cloud condensation nuclei, and ice-nucleating particles over the North Pacific Ocean, Bering Sea, and Arctic Ocean

Abstract. We investigated the association of marine biological indicators (polysaccharides, protein-like gel particles, and chl a) with the formation of fluorescent aerosol particles, cloud condensation nuclei (CCNs), and ice-nucleating particles (INPs) over the North Pacific Ocean, Bering Sea, and Arctic Ocean during September–November 2019. The abundance of bioindicators was high in the North Pacific Ocean and the Bering Sea (e.g., up to 1.3 mg m−3 of chl a), suggesting high biological activity due to a phytoplankton bloom. In the North Pacific Ocean, particles were characterized by high mass fractions of organics and sulfate with a predominance of terrestrial air masses. Conversely, in the Bering Sea and the Arctic Ocean, particles were characterized by high mass fractions of sea salt and sulfate with a predominance of maritime air masses. The averaged range/value of the CCN concentration at 0.4 % supersaturation were 99–151, 43–139, and 36 cm−3 over the North Pacific Ocean with terrestrial influences, over the Bering Sea with marine biogenic influences, and over the Arctic Ocean with marine influences, respectively, and the corresponding range/value of the hygroscopicity parameter κ were 0.17–0.59, 0.42–0.68, and 0.66, respectively. The averaged INP concentration (NINP) measured at temperatures of −18 and −24 ∘C with marine sources in the North Pacific and Bering Sea was 0.01–0.09 and 0.1–2.5 L−1, respectively, and that over the Arctic Ocean was 0.001–0.016 and 0.012–0.27 L−1, respectively. When marine sources were dominant, fluorescent bioaerosols in the fine mode were strongly correlated with all bioindicator types (R: 0.81–0.88) when the effect of wind-induced uplift from the sea surface to the atmosphere was considered. Correlations between NINP measured at −18 and −24 ∘C and all bioindicator types (R: 0.58–0.95 and 0.79–0.93, respectively) were positive, even when the extreme outlier point was omitted, as were those between NINP and fluorescent bioaerosols (R: 0.50 and 0.60, respectively), suggesting that marine bioindicators contributed substantially as sources of bioaerosols and to cloud formation.

Assessment of indoor bioaerosol exposure using direct-reading versus traditional methods—potential application to home health care

Home healthcare workers (HHCWs) can be occupationally exposed to bioaerosols in their clients’ homes. However, choosing the appropriate method to measure bioaerosol exposures remains a challenge. Therefore, a systematic comparison of existing measurement approaches is essential. Bioaerosol measurements with a real-time, fluorescence-based Wideband Integrated Bioaerosol Sensor (WIBS) were compared to measurements with four traditional off-line methods (TOLMs). The TOLMS included optical microscopic counting of spore trap samples, microbial cultivation of impactor samples, qPCR, and next-generation sequencing (NGS) of filter samples. Measurements were conducted in an occupied apartment simulating the environments that HHCWs could encounter in their patients’ homes. Descriptive statistics and Spearman’s correlation test were computed to compare the real-time measurement with those of each TOLM. The results showed that the geometric mean number concentrations of the total fluorescent aerosol particles (TFAPs) detected with the WIBS were several orders of magnitude higher than those of total fungi or bacteria measured with the TOLMs. Among the TOLMs, concentrations obtained with qPCR and NGS were the closest to the WIBS detections. Correlations between the results obtained with the WIBS and TOLMs were not consistent. No correlation was found between the concentrations of fungi detected using microscopic counting and any of the WIBS fluorescent aerosol particle (FAP) types, either indoors or outdoors. In contrast, the total concentrations detected with microbial cultivation correlated with the WIBS TFAP results, both indoors and outdoors. Outdoors, the total concentration of culturable bacteria correlated with FAP-type AC. In addition, fungal and bacterial concentrations obtained with qPCR correlated with FAP types AB and AC. For a continuous, high-time resolution but broad scope, the real-time WIBS could be considered, whereas a TOLM would be the best choice for specific and more accurate microbial characterization. HHCWs’ activities tend to re-aerosolize bioaerosols causing wide temporal variation in bioparticle concentrations. Thus, the advantage of using the real-time instrument is to capture those variations. This study lays a foundation for future exposure assessment studies targeting HHCWs.

Airborne Microbial Aerosol Detection by Combining Single Particle Mass Spectrometry and a Fluorescent Aerosol Particle Sizer.

Detection methods for microbiological aerosols based on single particle mass spectrometry (SPAMS) and a fluorescent aerosol particle sizer (FLAPS) have been developed progressively. However, they encounter interference and inefficiency issues. By merging FLAPS and SPAMS technologies, the majority of inorganic ambient aerosols may be eliminated by the FLAPS, thus resolving SPAMS' large data volume. SPAMS, on the other hand, may eliminate the secondary fluorescence interference that plagues the FLAPS. With the addition of the enhanced machine learning classifier, it is possible to extract microbial aerosol signals more precisely. In this work, a FLAPS-SPAMS instrument and a Random Forest classifier based on Kendall's correlation expansion training set approach were built. In addition to analyzing the outdoor microbial proportions, the interference components of non-microbial fluorescent particles were also examined. Results indicate that the fraction of outdoor microbial aerosols in fluorescent particles is 25.72% or roughly 2.57% of total particles. Traditional ART-2A algorithm and semi-empirical feature clustering approaches were used to identify the interference categories of abiotic fluorescent particles, which were mostly constituted of EC/OC, LPG/LNG exhaust, heavy metal organics, nicotine, vinylpyridine, polycyclic aromatic hydrocarbons (PAHs), and polymers, accounting for 68.51% of fluorescent particles.

Biological and Nonbiological Sources of Fluorescent Aerosol Particles in the Urban Atmosphere.

Online detection of bioaerosols based on the light-induced fluorescence (LIF) technique is still challenging due to the complexity of bioaerosols and the external/internal mixing with nonbiological fluorescent compositions. Although many lab studies have measured the fluorescence properties of the biological and nonbiological materials, there is still a scarcity of knowledge of the sources of fluorescent aerosol particles (FAP) in the ambient atmosphere. Here, we fill this gap by combining the online measurement of an LIF-based instrument (wideband integrated bioaerosol sensor, WIBS, 0.8-20 μm) with the measurements of typical biological matter and the compositions related to major nonbiological FAP from May to July in the megacity Beijing. We find that fungal spores and pollen are widely observed in all types of FAP using a WIBS. Bacteria are suggested to be associated with the fine mode FAP (excitation/emission: 280 nm/310-400 nm; 0.8-3 μm). The FL-B and -BC particles (emission in 420-650 nm) contributing the most to FAP are strongly associated with humic-like substances, dust, burning and combustion emissions, and secondary organic aerosols (SOA). This study provides a guide for interpreting individual FAP measured by LIF instruments and points to the applicability of online LIF instruments to characterize nonbiological compositions including SOA.

Observation of bioaerosol transport using wideband integrated bioaerosol sensor and coherent Doppler lidar

Abstract. Bioaerosols are usually defined as aerosols arising from biological systems such as bacteria, fungi, and viruses. They play an important role in atmospheric physical and chemical processes including ice nucleation and cloud condensation. As such, their dispersion affects not only public health but also regional climate. Lidar is an effective technique for aerosol detection and pollution monitoring. It is also used to profile the vertical distribution of wind vectors. In this paper, a coherent Doppler wind lidar (CDWL) is deployed for aerosol and wind detection in Hefei, China, from 11 to 20 March in 2020. A wideband integrated bioaerosol sensor (WIBS) is used to monitor variations in local fluorescent bioaerosols. Three aerosol transport events are captured. The WIBS data show that, during these transport events, several types of fluorescent aerosol particles exhibit abnormal increases in their concentration, number fractions to total particles, and number fractions to whole fluorescent aerosols. These increases are attributed to external fluorescent bioaerosols instead of local bioaerosols. Based on the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) backward trajectory model and the characteristics of external aerosols in WIBS, their possible sources, transport paths, and components are discussed. The results prove the influence of external aerosol transport on local high particulate matter (PM) pollution and fluorescent aerosol particle composition. The combination of WIBS and CDWL expands the aerosol monitoring parameters and provides a potential method for real-time monitoring of fluorescent biological aerosol transport events. In addition, it also helps to understand the relationships between atmospheric phenomena at high altitudes like virga and the variation of surface bioaerosol. It contributes to the further understanding of long-range bioaerosol transport, the roles of bioaerosols in atmospheric processes, and in aerosol–cloud–precipitation interactions.

Real-time measurements of fluorescent aerosol particles in a living laboratory office under variable human occupancy and ventilation conditions

The abundance of super-micron biological and abiotic particles in occupied indoor environments can be influenced by time-dependent changes in human-associated emissions and building ventilation conditions. Real-time measurements of fluorescent aerosol particles (FAPs) were integrated with a building sensing platform to evaluate the influence of human occupancy and ventilation on the temporal dynamics of fluorescent biological and abiotic particles in a living laboratory office. Concentrations and size distributions of FAPs were measured via laser-induced fluorescence (LIF). Human occupants were identified as a major source of super-micron FAPs in mechanically ventilated office buildings. Mass concentrations and size distributions of FAPs larger than 3 μm scaled with human occupancy in the office. Detailed single particle fluorescence data indicated that human-associated emissions enriched the office atmosphere with specific FAP types that varied in morphology. Office occupants were strong emitters of ABC-type particles (number and mass), and to a lesser extent, A-type particles (number and mass), AB-type particles (mass), and B-type particles (mass). Such FAP types are related to common indoor bacterial and fungal aerosols and fluorescent clothing fabric fibers. The introduction of natural ventilation via a double skin glass façade increased the indoor abundance of FAPs due to the efficient transport of outdoor FAPs into the office. While LIF provides valuable real-time data on indoor FAP dynamics, it lacks specificity and cannot fully resolve the origins of fluorescent biological and abiotic particles in indoor spaces.

Human Emissions of Size-Resolved Fluorescent Aerosol Particles: Influence of Personal and Environmental Factors.

Human emissions of fluorescent aerosol particles (FAPs) can influence the biological burden of indoor air. Yet, quantification of FAP emissions from human beings remains limited, along with a poor understanding of the underlying emission mechanisms. To reduce the knowledge gap, we characterized human emissions of size-segregated FAPs (1-10 μm) and total particles in a climate chamber with low-background particle levels. We probed the influence of several personal factors (clothing coverage and age) and environmental parameters (level of ozone, air temperature, and relative humidity) on particle emissions from human volunteers. A material-balance model showed that the mean emission rate ranged 5.3-16 × 106 fluorescent particles per person-h (0.30-1.2 mg per person-h), with a dominant size mode within 3-5 μm. Volunteers wearing long-sleeve shirts and pants produced 40% more FAPs relative to those wearing t-shirts and shorts. Particle emissions varied across the age groups: seniors (average age 70.5 years) generated 50% fewer FAPs compared to young adults (25.0 years) and teenagers (13.8 years). While we did not observe a measurable influence of ozone (0 vs 40 ppb) on human FAP emissions, there was a strong influence of relative humidity (34 vs 62%), with FAP emissions decreasing by 30-60% at higher humidity.

Abundance and Diurnal Trends of Fluorescent Bioaerosols in the Troposphere over Mt. Tai, China, in Spring

AbstractPrimary biological aerosol particles are ubiquitous in the global atmosphere and can affect cloud formation, deteriorate air quality, and cause human infections. Mt. Tai (1,534 m a.s.l.) is an elevated site in the North China Plain where atmospheric aerosols reflect both regional advection and long‐range transport. In this study, we deployed a Wideband Integrated Bioaerosol Sensor (WIBS‐4A) and collected total suspended particles and eight‐stage size‐segregated aerosol samples at the summit of Mt. Tai in spring from 21 March to 8 April 2017 to quantify the abundance, size distributions, and diurnal variations of fluorescent bioaerosols and to investigate the effect of different fluorescence thresholds of WIBS for ambient bioaerosol recognition. During the whole sampling period, the number concentration of fluorescent particles (>0.8 μm) was 647 ± 533 L−1, accounting for 26.9% ± 10.0% by number of the total particles in that size range. Three‐dimensional excitation‐emission matrix fluorescence of water‐soluble organic matter in size‐segregated aerosols shows that humic‐like substances (HULIS) are mainly in the fine mode (<2.1 μm) while protein‐like substances are mainly in the coarse mode (>2.1 μm). From the diurnal variation, it is shown that bioaerosols can undergo transformation during long‐range transport and contribute to HULIS. For bioaerosol recognition, we find that 6σ‐threshold can lead to better classification of fluorescent aerosol particles for fungal spores. Overall, our results constrain the abundance of primary bioaerosols in the troposphere over East Asia and elucidate the processes for their evolution via mountain/valley breezes and long‐range transport.

The Deposition of Submicron Fluorescent Aerosol Particles by a Closed-Loop Flow System

An aerosol flow system has been constructed to mimic the delivery of particles to the air-liquid interface. A colloidal suspension of submicron fluorescent core-shell silica-based particles was sprayed by an ultrasonic nebulizer. The dynamics of the aerosol settling was investigated by numerical simulation to determine the carrier gas flow rate, which was further verified through experimentation. Fluorescent microscopy, a non-vacuum imaging technique, was used to observe the particles deposited on the substrate. It was found that the apparent (fluorescent) size distribution was shifted from 2.9 ± 6.0 μm to 1.7 ± 2.2 μm, which is correlated to the shift in the aggregate size from 0.70 μm to 0.24 μm due to the changes in the colloidal suspension concentration. In addition, the uniformity of the particles dispersed on the substrate was not significantly affected by the suspension’s concentration, as confirmed by the inter-particle distance analysis. It is therefore suggested that the method presented here may potentially be applied for the deposition and analysis of submicron particles on various types of substrate (i.e. air-liquid interface) without the need for vacuum imaging analysis (e.g. electron microscopy).

Review: The Use of Real-Time Fluorescence Instrumentation to Monitor Ambient Primary Biological Aerosol Particles (PBAP)

Primary biological aerosol particles (PBAP) encompass many particle types that are derived from several biological kingdoms. These aerosol particles can be composed of both whole living units such as pollen, bacteria, and fungi, as well as from mechanically formed particles, such as plant debris. They constitute a significant proportion of the overall atmospheric particle load and have been linked with adverse health issues and climatic effects on the environment. Traditional methods for their analysis have focused on the direct capture of PBAP before subsequent laboratory analysis. These analysis types have generally relied on direct optical microscopy or incubation on agar plates, followed by time-consuming microbiological investigation. In an effort to address some of these deficits, real-time fluorescence monitors have come to prominence in the analysis of PBAP. These instruments offer significant advantages over traditional methods, including the measurement of concentrations, as well as the potential to simultaneously identify individual analyte particles in real-time. Due to the automated nature of these measurements, large data sets can be collected and analyzed with relative ease. This review seeks to highlight and discuss the extensive literature pertaining to the most commonly used commercially available real-time fluorescence monitors (WIBS, UV-APS and BioScout). It discusses the instruments operating principles, their limitations and advantages, and the various environments in which they have been deployed. The review provides a detailed examination of the ambient fluorescent aerosol particle concentration profiles that are obtained by these studies, along with the various strategies adopted by researchers to analyze the substantial data sets the instruments generate. Finally, a brief reflection is presented on the role that future instrumentation may provide in revolutionizing this area of atmospheric research.

Fluorescent bioaerosol particle, molecular tracer, and fungal spore concentrations during dry and rainy periods in a semi-arid forest

Abstract. Bioaerosols pose risks to human health and agriculture and may influence the evolution of mixed-phase clouds and the hydrological cycle on local and regional scales. The availability and reliability of methods and data on the abundance and properties of atmospheric bioaerosols, however, are rather limited. Here we analyze and compare data from different real-time ultraviolet laser/light-induced fluorescence (UV-LIF) instruments with results from a culture-based spore sampler and offline molecular tracers for airborne fungal spores in a semi-arid forest in the southern Rocky Mountains of Colorado. Commercial UV-APS (ultraviolet aerodynamic particle sizer) and WIBS-3 (wideband integrated bioaerosol sensor, version 3) instruments with different excitation and emission wavelengths were utilized to measure fluorescent aerosol particles (FAPs) during both dry weather conditions and periods heavily influenced by rain. Seven molecular tracers of bioaerosols were quantified by analysis of total suspended particle (TSP) high-volume filter samples using a high-performance anion-exchange chromatography system with pulsed amperometric detection (HPAEC-PAD). From the same measurement campaign, Huffman et al. (2013) previously reported dramatic increases in total and fluorescent particle concentrations during and immediately after rainfall and also showed a strong relationship between the concentrations of FAPs and ice nuclei (Huffman et al., 2013; Prenni et al., 2013). Here we investigate molecular tracers and show that during rainy periods the atmospheric concentrations of arabitol (35.2 ± 10.5 ng m−3) and mannitol (44.9 ± 13.8 ng m−3) were 3–4 times higher than during dry periods. During and after rain, the correlations between FAP and tracer mass concentrations were also significantly improved. Fungal spore number concentrations on the order of 104 m−3, accounting for 2–5 % of TSP mass during dry periods and 17–23 % during rainy periods, were obtained from scaling the tracer measurements and from multiple analysis methods applied to the UV-LIF data. Endotoxin concentrations were also enhanced during rainy periods, but showed no correlation with FAP concentrations. Average mass concentrations of erythritol, levoglucosan, glucose, and (1 → 3)-β-D-glucan in TSP samples are reported separately for dry and rainy weather conditions. Overall, the results indicate that UV-LIF measurements can be used to infer fungal spore concentrations, but substantial development of instrumental and data analysis methods appears to be required for improved quantification.

Ambient measurement of fluorescent aerosol particles with a WIBS in the Yangtze River Delta of China: potential impacts of combustion-related aerosol particles

Abstract. Fluorescence characteristics of aerosol particles in a polluted atmosphere were studied using a wideband integrated bioaerosol spectrometer (WIBS-4A) in Nanjing, Yangtze River Delta area of China. We observed strong diurnal and day-to-day variations of fluorescent aerosol particles (FAPs). The average number concentrations of FAPs (1–15 µm) detected in the three WIBS measurement channels (FL1: 0.6 cm−3, FL2: 3.4 cm−3, FL3: 2.1 cm−3) were much higher than those observed in forests and rural areas, suggesting that FAPs other than bioaerosols were detected. We found that the number fractions of FAPs were positively correlated with the black carbon mass fraction, especially for the FL1 channel, indicating a large contribution of combustion-related aerosols. To distinguish bioaerosols from combustion-related FAPs, we investigated two classification schemes for use with WIBS data. Our analysis suggests a strong size dependence for the fractional contributions of different types of FAPs. In the FL3 channel, combustion-related particles seem to dominate the 1–2 µm size range while bioaerosols dominate the 2–5 µm range. The number fractions of combustion-related particles and non-combustion-related particles to total aerosol particles were ∼ 11 and ∼ 5 %, respectively.

Ground‐based measurement of fluorescent aerosol particles in Tokyo in the spring of 2013: Potential impacts of nonbiological materials on autofluorescence measurements of airborne particles

AbstractWe present results from the observation of fluorescent (FL) aerosols in Tokyo in the spring of 2013. Ambient aerosol particles were analyzed using a single‐particle laser‐induced fluorescence instrument. The fluorescent emission from a single particle excited by a pulsed UV laser (excitation wavelength of 263 nm) was detected by three photomultiplier tubes with band‐pass filters (fluorescence wavelength of 335–379, 420–500, and 500–600 nm). Fluorescence patterns from single particles were analyzed for investigating fluorophores and their sources using backward trajectory analysis, factor analysis, and a comparison with other tracer observations. The backward trajectory analysis suggested possible influences of long‐range transport from northern China in some cases. Observed supermicron FL aerosols were classified into two types: combustion‐ and dust‐type particles. The detection of combustion‐type FL aerosols, which showed temporal variations similar to nitrogen oxides and elemental carbon, implied the presence of polyaromatic hydrocarbons (PAHs) and their derivatives. Dust‐type FL aerosols, which were well correlated with the lidar‐derived dust‐aerosol optical depth near the surface (<1 km) and with mineral ions, were dominant in the supermicron size range. The number concentrations of coarse FL aerosols (≥2 µm), with which nonnegligible levels of fluorescence were recorded in all three channels, increased during Asian dust events (relative to a local dust event). It is suggested that PAHs and/or biological materials mixed with dust particles were transported from the North China Plain to the outflow region in East Asia during the observation period. Moreover, the autofluorescence measurement of airborne particles can be substantially affected by nonbiological materials in this region.

Observations of fluorescent and biological aerosol at a high-altitude site in central France

Abstract. Total bacteria, fungal spore and yeast counts were compared with ultraviolet-light-induced fluorescence (UV-LIF) measurements of ambient aerosol at the summit of the Puy de Dôme (PdD) mountain in central France (1465 m a.s.l), which represents a background elevated site. Bacteria, fungal spores and yeast were enumerated by epifluorescence microscopy (EFM) and found to number 2.2 to 23 L−1 and 0.8 to 2 L−1, respectively. Bacteria counts on two successive nights were an order of magnitude larger than in the intervening day. A wide issue bioaerosol spectrometer, version 3 (WIBS-3) was used to perform UV-LIF measurements on ambient aerosol sized 0.8 to 20 μm. Mean total number concentration was 270 L−1 (σ = 66 L−1), found predominantly in a size mode at 2 μm for most of the campaign. Total concentration (fluorescent + non-fluorescent aerosol) peaked at 500 L−1 with a size mode at 1 μm because of a change in air mass origin lasting around 48 h. The WIBS-3 features two excitation and fluorescence detection wavelengths corresponding to different biological molecules, although non-biological interferents also contribute. The mean fluorescent particle concentration after short-wave (280 nm; associated with tryptophan) excitation was 12 L−1 (σ = 6 L−1), and did not vary much throughout the campaign. In contrast, the mean concentration of particles fluorescent after long-wave (370 nm; associated with NADH) excitation was 95 L−1 (σ = 25 L−1), and a nightly rise and subsequent fall of up to 100 L−1 formed a strong diurnal cycle in the latter. The two fluorescent populations exhibited size modes at 3 μm and 2 to 3 μm, respectively. A hierarchical agglomerative cluster analysis algorithm was applied to the data and used to extract different particle factors. A cluster concentration time series representative of bacteria was identified. This was found to exhibit a diurnal cycle with a maximum peak appearing during the day. Analysis of organic mass spectra recorded using an aerosol mass spectrometer (AMS; Aerodyne Inc.) suggests that aerosol reaching the site at night was more aged than that during the day, indicative of sampling the residual layer at night. Supplementary meteorological data and previous work also show that PdD lies in the residual layer/free troposphere at night, and this is thought to cause the observed diurnal cycles in organic-type and fluorescent aerosol particles. Based on the observed disparity between bacteria and fluorescent particle concentrations, fluorescent non-PBA is likely to be important in the WIBS-3 data and the surprisingly high fluorescent concentration in the residual layer/free troposphere raises questions about a ubiquitous background in continental air during the summer.

Fluorescence spectra and elastic scattering characteristics of atmospheric aerosol in Las Cruces, New Mexico, USA: Variability of concentrations and possible constituents and sources of particles in various spectral clusters

The UV-excited laser-induced-fluorescence (UV-LIF) spectra of single atmospheric particles and the three-band integrating-nephelometer elastic scattering of atmospheric aerosol were measured during four approximately 24-h periods on May 2007 in Las Cruces, New Mexico, USA. Aerosol scattering measurements in the nephelometer red channel (50-nm band centered at 700-nm) ranged from around 3–10 times the molecular (Rayleigh) scattering background. On average 22.8% of particles with size greater than about 1 μm diameter have fluorescence above a preset fluorescence threshold. A hierarchical cluster analysis indicates that most of the single-particle UV-LIF spectra fall into about 10 categories (spectral clusters) as found previously at other geographic sites (Pinnick et al., 2004; Pan et al., 2007). The clusters include spectra characteristic of various humic/fulvic acids, humic-like-substances (HULIS), chemically aged terpenes, fungal spores, polycyclic aromatic hydrocarbons, bacteria, cellulose/pollens, and mixtures of various organic carbon compounds. By far the most populated cluster category is similar to those of chemically aged terpenes/humic-materials; on average this population comprises about 62% of fluorescent particles. Clusters with spectra similar to that of some HULIS aerosol contain on average 10.0% of particles; those characteristic of some fungal spores (or perhaps mixtures of aromatic organic compounds) 8.4% of particles; bacteria-like spectra 1.6% of particles; and cellulose/pollen-like spectra 0.8% of particles. Measurements of fluorescent particles over relatively short (24 min) periods reveal that the concentrations of particles in the most populated clusters are highly correlated, suggesting that the particles populating them derive from the same region; these particles might be composed of crustal material coated with secondary organic carbon. On the other hand, concentrations of particles having cellulose-like spectra are generally uncorrelated with those in any other cluster. No clear distinction in fluorescent aerosol characteristics can be seen for different air mass trajectories arriving at the sampling site, suggesting that fluorescent aerosol particles are primarily of local origin. Integrations of the single-particle UV-LIF spectra over approximate 24 h time intervals reveal two broad peaks around 350 nm and 450 nm (for 263 nm excitation); the 450 nm peak is somewhat similar to that measured previously for water soluble organic carbon derived from aerosol collections. The 350 nm peak apparently has not been seen before in measurements of aerosol collections and may derive from non-soluble primary biological aerosol particles such as fungal spores. Further measurements are needed to investigate in more detail the generality of these results.

Characterization of a novel particle into liquid sampler for analysis of single fluorescent aerosol particles through capillary electrophoresis

An approach to sample and analyze single aerosolized droplets (<10 nL) of solutions containing fluorescein isothiocyanate (FITC) labeled glycine (GLY) and glutamic acid (GLU) is demonstrated. The sampling approach is based on inertial impaction in which the sample particle is accelerated through a nozzle and directly into a small drop of buffered solution (20 mM borate, pH = 10) suspended at the end of a coaxial tube of stainless steel and a fused silica capillary. A spherical light scattering cell and laser ( λ = 532 nm) is used to detect the arrival of particles at the buffered droplet. Upon dissolution and/or mixing, a portion of the sample is injected onto the fused silica capillary for subsequent chemical analysis by capillary electrophoresis (CE) and detection by laser-induced fluorescence (LIF). It was found that the inertial impaction approach sampled particles >1 μm diameter with an efficiency of 80% or greater. At 15 kV applied potential, the FITC conjugates of GLY and GLU could be resolved in less than 120 s allowing qualitative analysis of the contents of single dispersed particles. However, the extent to which the sample is diluted into the buffer droplet varied significantly on a per-particle basis that caused >80% R.S.D. in fluorescence peak heights. This aspect of the method would necessitate the use of internal standards for quantitative analysis of materials present within the particles. It is envisaged that further improvements to the device described may ultimately lead to analysis of the contents of single particles dispersed in earth's atmosphere.