Measurement Methods - Term Paper Example

The measurement techniques of Particulate Matter 2.5 (PM2.5) Introduction: The major source of particulate matter is industrialization and urbanization (Vladimir, 2003). Although the industrialization and urbanization are the main air pollutants, the contribution of bushfires cannot be neglected especially in some of the countries. In the past several bushfires have taken place in different parts of the world. In bushfire, the biomass burns and produces suspended particles of various dimensions, carbon and other metals and trace elements. Burning of savannas in Australia accounts for an estimated 60-75% carbon released by the Australian biomass fires (Vanderzalm, 2003). An earlier research has shown a relationship between hydrogen and a trace element (ANSTO, 2003). For analyzing these suspended particulate matters, these particles have to be collected as per a standard procedure and thereafter have to be investigated. For analyzing the nature of these suspended particles especially PM2.5 various analytical techniques are used. Analytical techniques such as particle induced X-ray emission or particle induced gamma ray emission; IR spectroscopy and gas chromatography are used for finding the elements, inorganic compounds and organic compounds respectively (Measurement methods, 2007). In the present study a literature search has been carried out to study the impact of bushfires on our environment and the examples of Australia and Singapore bush fires has been covered. A brief introduction of PM2.5 has also been covered. A few analytical instruments utilized by the various environmental protection agencies have been studied with respect to their advantages in bushfires. The through principles of the instrument techniques were also studied and a conclusion of the study has been made. Particulate Matter 2.5 (PM2.5) The most common measurement in air quality is the concentration of suspended particles in it and is reported as the PM index. As these suspended particles are not in homogeneous conditions so these are reported as microgram of particulate matter per cubic meter of air i.e. g/m3. Small-suspended particles in air have detrimental affect on human health and therefore these smaller particles having lower than specified diameters are collected, analyzed and reported. PM10 (where the total concentration of all particles having diameter less than 10 m) are being monitored by various government agencies in many countries such as US, Canada (Baird, 2005). Many government agencies are also looking for monitoring fine suspended particles having diameter less than 2.5 m, as these are within the respirable range and can penetrate deep into the lungs. US EPA specification for PM 2.5 US EPA National Ambient Air Quality standards (NAAQS) have set standards for particulate matter PM2.5 and PM10. For PM2.5 it has set an annual average of 15 g/m3 with a 24 hour standard of 65g/m3 and for PM10 an annual average of 50 g/m3 with a 24-hour standard of 150 g/m3 (ANSTO, 2003). A short term US EPA NAAQS standard for air borne particulate matter is given in Table-1. As many countries still do not have their own specifications for PM2.5, most of the countries follow US EPA guidelines. Sampling of Particulate Matters: It is really difficult to collect a representative sample especially from a bushfire. However the sample should be collected from multiple locations so that the analysis gives more prcis and meaningful results. The sample collected from different part can either be mixed or separate analysis can be carried out. There are various methods involved for collecting particulate matters. A few methods are summarized below. a) Filter cups: Filters are the simplest way of collecting particulate matters. Aerosol sample is passed through a set of filters at a controlled rate so that a specific particulate matters are collected through a specific filter. These filter papers are cellulose, glass fiber, teflon or a combination of materials (Thompson, 1998). b) Cyclones: Cyclones are cheap and accurate enough to meet the modern requirement of collecting different sized particulate matters (Fly, 2007). Cyclone uses special type of impactors where the particles get separated due to impaction combined with gravitational settling. The advantage of cyclones is that the large particles get trapped in the walls and thus we get a designed size particulate matters only. c) Cascade Impactors: In cascade impactors, a large number of impactor stages are connected in series with smaller and smaller cut off diameter. The cut off diameters designs generally depends upon the air velocity and geometry of the stage. The disadvantage of this technique is the risk of bounce off from one stage to the next and obtaining sharp cut-off diameters in the last stages. Analytical Techniques: Scientist's especially analytical chemists assess these aerosols or particulate matters for their constituents. The constituents of this particulate matter especially PM2.5 can tell us about their detrimental effect on human health. The Particulate matter contains a wide range of inorganic ions, trace metals, elemental carbon and organic compounds. A few analytical methods are used for further investigation of these particulate matters. a) Ion Beam Analysis: Ion beam analysis is more commonly used for analysis of various particulate matters. A high-energy proton beam is generated from a source. The high-energy beam is accelerated to excite the element in the particulates from the filter. The excited elements scatter protons or emit radiations that can be identified for the specific elements and their compositions. Examples of ion beam analysis includes proton induced X-ray emission (PIXE), proton induced gamma ray emission (PIGME) and proton elastic scattering (PESA). b) X-ray Fluorescence: In this technique a monochromatic X-ray is bombarded to the particulate matter. The X-ray causes the element to emit X-rays. The wavelength and intensities of the single are indicators of specific element and the amount of element present in the sample. c) Ion Chromatography: Ion chromatography is most widely used for identifying ions in aerosols or particulate matters (Thompson, 1998). The technique uses a column through which the particulate matter in a solution is passed. Ions are separated by ion exchange and can be identified by electrical conductivity method. Principles and advantages and disadvantages of Analytical Techniques: a) Basic physical principles for particle induced Gamma-ray Emission: The principle of the analytical technique is based on the characteristics emission of gamma rays from the nucleus of an element, which is bombarded by a highly charged particle such as photon. The bombarded photon should have enough energy to overcome the repulsive coulomb forces so that it can penetrate and interact with nucleus. Due to it interaction, high energy x-rays are emitted from nucleus also known as gamma rays and is therefore used to identity and quantify the element present in the particulate matter. Advantages and disadvantages of PIGE (Particle induced gamma ray emission): Lighter elements of the periodic table have low nuclear charge and as the bombarding photon also have a low nuclear charge, the photons may not overcome the repulsive forces and hence can not penetrate and interact with the nucleus. So, the lighter element, Lithium, Sodium, magnesium and Aluminum cannot be detected by this technique, however if PIGE used in conjunction with PIXE can detect these elements. b) Basic Physical principle for X-Ray Fluorescence: Wavelength dispersive XRF is based on Bragg's law that states that the path difference between diffracted ray is directly proportional to wavelength. According to Braggs law n = 2d sin The technique uses a single crystal for which the 2d is kept constant and it acts as spectrum analyzer. X-rays are bombarded to the sample of particulate matters and the wavelength of emitted X-rays is measured. These are characteristics to the specific elements present in the sample of particulate matter. Advantages and disadvantages of XRF: XRF is a non-destructive technique and a small sample quantity is required to carry out the analysis. Further the technique is very much useful for sequential analysis and thus by measuring the different wavelength corresponding to different element, the whole elemental composition of the particulate matter can be found out. The main disadvantage of the technique is that it is not suitable for lighter elements and is used for elements heavier than magnesium. d) Basic physical principle of Ion Chromatography (IC): Chromatography is a 100-year-old technique of physical method of separation. M. S. Taswett in 1906-07 first separated chlorophyll on CaCO3 using petroleum ether. The sample in solution is passed through a column containing a particular resin, which act as a stationary phase. Different ions have characteristics affinity for the stationary phase i.e. resin and thus get separated. Thus in the chromatography technique, particulate matter solution is carried by mobile phase through the stationary phase and the adsorption - desorption takes many times as the analyte moves through the stationary phase and thus the separation is achieved as the components emerge at different time intervals. The separation is followed by detection, identification and quantification techniques. The detectors are an important part of the whole analysis technique and a few detectors such as Flame Ionization detectors are widely used. Advantage and disadvantage of Ion chromatography: This is the most common and simple technique used for identification of various compounds. The main disadvantage of the technique is that it is time consuming. Receptor Modeling: It is one of the most important parts of any particulate matter study and it is used to identify and quantify the emission sources. The technique uses the elemental composition obtained from different analytical techniques as mentioned above and infer the possible source as well as the level of damage to the environment by these particulate matters. The receptor modeling consists of two parts one the elemental fingerprinting and the other source apportionment (Thompson, 1998). There are two types of receptor model one the principle component analysis (PCA) or factor analysis and the other chemical mass balance (CMB) models. CMB (Chemical Mass Balance) method was used by many researchers for identification and quantification of the particulate matters (NCBI, 2005) Application of analytical techniques: Ion beam analysis has been widely used for detailed investigation of particulate matter (PM2.5) by various organizations worldwide. Scientists investigated in detailed the elements present in Particulate matter (PM2.5) in and around Sydney with the help of ion beam analysis (ANSTO, 2003). Scientists in a separate study in Los Angeles used chemical mass balance model for apportioning PM2.5 (Department of civil Engg., 07) Many scientists use chromatography for finding the different pollutants especially in bushfire (Nollet, 2005). There are a number of inorganic and organic components in the fine particles that are harmful for human beings. Chromatographically these constituents are identified (Naeher, 2005). SRF techniques has widely been used by the scientists for investigation of particulate matters especially PM 2.5 after bushfire (Larson, 2004). The technique is most suitable for identifying the elements by this non-destructive technique. Conclusion: Although bushfire are not common in some parts of the worlds but these plays a significant role in environmental conditions in certain dry regions. The pollutants are several in case of bushfire including inorganic and organic compounds. The study here has been focused on the particulate matter (PM2.5) and their analysis using an analytical technique. Fine particles especially particulate matter (PM2.5) forms due to condensation of combustion gases and incomplete combustion of organic materials. Scientists (Sutherland, 2005) have reported that with the increase of particulate matter, the respiratory symptoms such as dyspnea, cough, chest tightness, wheezing and sputum production increases. The particulate matter can further be analyzed for specific element or compound by using various analytical techniques. The common analytical techniques covered in this paper include ion beam analysis, XRF and ion chromatography. All the techniques have been found useful for quantifying the pollutants in particulate matters especially from bushfire. References: "Aerosol sampling newsletter" ANSTO, 28/1/2003, 17/3/07 http://www.ansto.gov.au/nugeo/iba/news/newsletters/newsletter28.pdf Bakhsin, Vladimir N., Environmental chemistry : Asian Lessons, Netherland : Kluwer Academic Publishers, 2003. Baird, Colin, Cann, Michael, Environmental Chemistry, New York: WH Freeman & Co., 2005. "Chemical mass balance model with fractionation for apportioning PM2.5 : a test case for Long Angeles traffic sources" NCBI, 2005, 16/3/2007 http://www.ncbi.nlm.nih.gov/entrez/query.fcgicmd=Retrieve&db=PubMed&list_uids=16 Larson,T, et al, Source apportionment of indoor, outdoor and personal PM2.5 in Seattle, Washington, Using positive matrix factorization, J. Air Waste Management Assoc, 2004, 54 (9), p. 1175-87. "Measurement Method II" Fy Chalmers, 17/3/07 < http://fy.chalmers.se/molnar/lectures/MeasurementMethodsII.htm> Naeher, Luke P et al, The university of Georgia's college of Public Health, Deptt of Environmental health science, March 31, 2005, 17/3/07 http://ehs.sph.berkley.edu/krsmith/publication/2005%20woodsmoke%20report%20Mar%2031%2005%20(rev).pdf Nollet, Neo M.L., Chromatographical Analysis of the Environment, Florida: CRC Press, 2005 "Particle Induced Gamma Ray Emission", Institute of Environmental Research, ANSTO, 17/3/07 < http://www.ansto.gov.au/nugeo/iba/capabilities/pige.htm> Sutherland, E,R, et al, Wildfire smoke and respiratory symptoms in patients with chronic obstructive pulmonary disease, Journal of Allergy and Clinical Immunology, 2005, 115(2), p.420-422. Vanderzalm, J.L. et al, Impact of Seasonal Biomass Burning on Air Quality in the Top End of Regional Northern Australia, Clean Air and Environmental Quality Volume 37, No. 3, pages 28-29. Table-1 US EPA NAAQS Standards for Airborne Particulate Matter Index (NAAQS) TSP (g/m3 ) PM10 (g/m3 ) PM2.5 (g/m3 ) Air Quality 0 to 50 51 to 100 101 to 200 201 to 300 >300 0 to 75 76 to 260 261 to 375 376 to 625 >626 0 to 50 51 to 150 151 to 350 351 to 420 >421 0 to 15 15 to 65 66 to 150 151 to 250 >251 Good Moderate Unhealthy V/Unhealthy Hazardous Read More