Single particle size and fluorescence spectra from

Authors: YongLe Pan Joshua D T Houck Pamela A Clark Ronald G Pinnick

Publish Date: 2013/03/25

Volume: 112, Issue: 1, Pages: 89-98

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Abstract

A singleparticle fluorescence spectrometer SPFS and an aerodynamic particle sizer were used to measure the fluorescence spectra and particle size distribution from the particulate emissions of 12 different burning materials in a tube furnace to simulate openair burning of garbage Although the particulate emissions are likely dominated by particles 1 μm diameter only the spectra of supermicron particles were measured here The overall fluorescence spectral profiles exhibit either one or two broad bands peaked around 300–450 nm within the 280–650 nm spectral range when the particles are illuminated with a 263nm laser Different burning materials have different profiles some of them cigarette hair uniform paper and plastics show small changes during the burning process and while others beef bread carrot Styrofoam and wood show big variations which initially exhibit a single UV peak around 310–340 nm and a long shoulder in visible and then gradually evolve into a bimodal spectrum with another visible peak around 430–450 nm having increasing intensity during the burning process These spectral profiles could mainly derive from polycyclic aromatic hydrocarbons with the combinations of tyrosinelike tryptophanlike and other humiclike substances About 68  of these singleparticle fluorescence spectra can be grouped into 10 clustered spectral templates that are derived from the spectra of millions of atmospheric aerosol particles observed in three locations while the others particularly these bimodal spectra do not fall into any of the 10 templates Therefore the spectra from particulate emissions of burning materials can be easily discriminated from that of common atmospheric aerosol particles The SFFS technology could be a good tool for monitoring burning pit emissions and possibly for distinguishing them from atmospheric aerosol particlesOpenair burn pits are widely used for disposal of garbage military waste and human waste on US military bases in Iraq and Afghanistan This practice has attracted much attention since hundreds war veterans claimed that they are suffering respiratory problems and believe that burn pit exposure is the major cause for their illnesses 1 2 3 Efforts have been taken to mitigate this practice Congress has passed legislation requiring the military to justify any further use of burn pits and the Pentagon is conducting a review of burn pits and their current status in Iraq and Afghanistan and has shut down many in Iraq The US Department of Defense and the Department of Veterans Affairs are proceeding cautiously in linking soldiers’ symptoms to the burn pits The Institute of Medicine National Academy of Science and other research institutes are conducting largescale studies The US Army Center for Health Promotion and Preventive Medicine USACHPPM the US Air Force Institute for Operational Health and the US Army Research Laboratory are conducting ambientair sampling and screening healthrisk assessments 3 4 5 6 7 8 Recently the Institute of Medicine reported that there is no evidence linking exposure to burn pits in Iraq and Afghanistan for longterm health problems 4 5 The investigation from a team of doctors found that burn pit exposure within 3–5 miles was not associated with respiratory outcomes after statistical adjustment However increased symptom reporting was observed among Air Force deployers located within 2 miles of Joint Base Balad which was marginally significant with no evidence of trend 7 Another team of doctors found that diffuse constrictive bronchiolitis might be associated with inhalational exposure in 38 soldiers 8Many chemicals that may present a health risk to service members were detected in the DoD air sampling from Joint Base Balad Iraq and Camp Lemonier Djibouti These samples include a particulate matter PM b polycyclic aromatic hydrocarbons PAHs c volatile organic compounds VOC and d toxic organic halogenated dioxins and furans TOHDF 9 Exposure to chemical toxins could affect the skin eyes respiration kidneys liver nervous system and cardiovascular system 10 11 12 13 Longduration inhalation of heavy PM emissions from natural and manmade sources can cause serious heart and lung health problems 9 10 11 12 13 Fortunately most of the eye irritation coughing and throat irritation breathing difficulties and skin itching are temporary for limited exposure to the burn pit emissions 10 It is very difficult to determine at the present stage how exposure to burn pit affects health with given limited scientific studies and the multitude of variables such as the variety of burning materials burning condition emitted particle size and concentration the duration of exposures nearsurface wind fields the closeness of service members to the pit and various human factors including age health status existing medical conditions and genetics 9 10 Further systematic and detailed studies are needed to understand the potential health effects caused by exposed to burn pit emissions The development of a realtime monitoring system to provide service members with the information they need to reduce exposure levels near burning pits could be helpfulOptical properties of atmospheric PM such as elastic scattering absorption fluorescence and Raman spectra have been used to characterize the dynamic variability aging process and chemical compositions of emission from biomass burning 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Studies found that scattering and absorption efficiency strongly correlated to particle size and black carbon BC content related to individual fire physics 14 Concentration of particlerelated reactive oxygenated species which is considered an important parameter in assessing the potential toxicological impact of particulate matter could be measured by fluorescence spectra 16 Black carbon concentrations in particulate organic matter from biomass burning can be deduced by observing pyrene fluorescence loss 17 Fluorescence and Raman spectra are good methods for characterizing the natural carbon clusters 18 Particle size morphology refractive index carbon and PAH contents help understand the emissions 19 20 21 22 More than 90  of the total aerosol mass in burning emissions could be particulates of organic carbon OC and BC within the dominated fine aerosols 25 μm 20 Chemical characterization and specification of the openair burning affluent may allow linking to potential health effects 9 10 11 12 13 23 24 25 26 The excitationemission matrix EEM can identify ultratrace amounts of particular PAHs humic substances dissolved organic carbon DOC in different complex samples 27 28 29 30 31 32 33 34 such as the determination of two of the most carcinogenic PAHs benzoapyrene and dibenzoah anthracene at a concentrations below 10 ng/L 27 The 370nm excited fluorescence intensity ratio between 450 and 500 nm named as fluorescence index FI was found to have a significant relationship with DOC concentrations for polluted stream water 29Technologies based on ultraviolet laserinduced fluorescence UVLIF are capable of realtime in situ detection and classification for biological and other organic carbon aerosols eg 35 36 37 38 see a review by DeFreez 39 A singleparticle fluorescence spectrometer SPFS ref 38 can obtain the dispersed fluorescence spectra 280–700 nm of individual airborne aerosol particles 1–10 μm size range as they flow through the sensor Such a nondestructive technique has the advantage of providing nearrealtime information related to the molecular compositions without requiring collection of particles handling of the samples or searching over a substrate for particles to be analyzed but lacks the ability to chemically identify or specify the composition of the particle as might be possible with mass spectroscopy or other biochemical analytical methodsIn this paper the SPFS technology is applied to measure singleparticle fluorescence spectra of the particulate emissions of the controlled burning of materials The materials were burned in a tube furnace to simulate burning from an openair burn pit In addition the particle size distribution was monitored by a TSI aerodynamic particle sizer The tube furnace was set to start at 300 °C and raised to a maximum 420 °C temperature until various test materials melted/smoldered and/or combusted Twelve materials were selected for burning to mirror the most common garbage produced daily on military bases such as plastics paper food wood clothing and Styrofoam The laboratory study described herein provides control and repeatability of burn conditions and measurements of the emission from individual burning materials which may not be achievable in an openair burn pit environmentThe purpose of this study is to assess the potential for monitoring particle emission from burn pits by the measurement of particle size and singleparticle fluorescence spectra Although the observed fluorescence spectral profiles are different for the various particulate emissions excited by a 263nm laser but this approach falls far short of identifying PM compositions It is even difficult to say at this early stage of research if this technology could effectively be used for monitoring particularly harmful emissions from a burn pit due to numerous possible molecules and many possible mixtures of molecules produced during the different burning phases burning conditions and aging processes These preliminary test results reveal the fluorescence spectra and size distributions of some common burn emissions under certain burn conditions The results suggest the UVLIF might be a useful complementary technology for realtime in situ monitoring of burn pits to protect the service members and limit their exposure to dangerous levels of harmful burn emissionsExperimental arrangement for measuring singleparticle ultraviolet laserinduced fluorescence UVLIF spectra and size of particulate emissions from various burning materials The UVLIF spectra are measured by a singleparticle fluorescence spectrometer SPFS The particle size distribution is monitored by an aerodynamic particle sizer TSI 3321

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