may 21 - Ch. 11 (Measurements) Requirements Analysis...

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Unformatted text preview: Ch. 11 (Measurements) Requirements Analysis choices Sampling platforms Importance of sampling Gas analysis Particle analysis Size measurements Off-line: Bulk (filter) analysis On-Line Bulk (Ion chromatography: PILS, AMS) Single particle analysis (ATOFMS) Ideal Requirements High sensitivity (low limit of detection) Wide dynamic range of concentrations 78% N 2 down to fraction of a ppt (for reactive trace gases) i.e. OH radical--0.1 ppt High time resolution Radicals reacts on second by second timescales Requires no sample collection required artifacts, slow (low time resolution) Selective Small Durable Low power consumption Inexpensive (multiple sampling locations) Analysis Choices What is your scientific question/hypothesis? Why are you making the measurements? Gas or particle phase? Necessary sensitivity Off-line or on-line? Particles Bulk or single particle? Metals, organic speciation, ions, soot, dust, sea salt? tmospheric Measurement Platforms Analytical Measurement Methods GASES (pp. 548-607 in F-Pitts)- Sampling (e.g. denuders, scrubbers, etc.) followed by quantification by ion chromatography (IC), colorimetric methods, electrochemical analysis, GC-MS, LC-MS, etc. - On-line methods being developed 1) Optical Spectroscopy Techniques Chemiluminescense Fluorescence Infrared and Raman (absorption) DOAS (UV-vis) 2) Mass spectrometry Denuder ff-line sampling uantification only as good as your sampling protocol Interferences often produce sampling artifacts Positive Negative here are the artifacts? Analytical Methods PARTICLES- Sampling: filters, impactors, electrostatic precipitators- Physical Properties - Mass : gravimetric methods, piezoelectric microbalance, oscillating microbalance- Size distributions: Optical particle counters (OPC), aerodynamic particle sizers (APS), differential mobility analyzers (DMA)- Chemical Composition (e.g., GC/MS, LC/MS, IC, single particle analysis) Particle Measurements Mass concentration ( g/m 3 ) Number concentration (#/cm 3 ) Mass fraction Number fraction PM 2.5 PM 10 TSP (total suspended particles) Physical properties Particle Size Metrics Geometric Electron microscopy Aerodynamic Aerodynamic particle sizer Mobility Scanning mobility particle sizer Optical Optical particle counter Lower limit about 200 nm. Balance between sheath flow and electrical Mobility Scan charge and one mobility size gets out at a time Detect in CPC by growing particles to detectable sizes Analyzes 10 nm up to 700 nm Differential mobility analyzer (3 nm up to 600-700 nm) Condenses isobutanol (or water) on particles to grow them to larger (detectable) sizes Dp density Da Aerodynamic Particle Sizer (APS) PM chemistry Secondary species: Sulfate, nitrate, ammonium, organic acids, Ion chromatography, PILS Organic carbon (OC) species...
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may 21 - Ch. 11 (Measurements) Requirements Analysis...

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