Field Methods of Monitoring Atmospheric Systems Chemical Analysis of Particulate Matter Copyright © 2006 by DBS

Sources e.g NH 4 Cl, SO 4 2- / NO 3 - salts Natural: forest fires, volcanoes etc. Man-made: fossil-fuel combustion, industry Mineral dust from weathering of rocks and soils Chemical composition can be used to ID source and fate

Typical Analysis Total particulate mass concentration e.g 70 μg m -3 rural 300 μg m -3 urban 10 mg m -3 factory workshop 100 mg m -3 power station flue gases Chemical Composition –Metals - highly insoluble silicates require dissolution –Inorganic ions –Organics –Size distribution –Total suspended particulate matter (TSP) Very small amounts means an exacting analytical task As a function of particle size

Question Why is particle size important? 1.Transport and removal – residence time depends on size 2.Physiological properties – smaller particles penetrate deeper into lungs 3.Distribution of chemical species 4.Effect on atmospheric reactions

Filters ProsConsUse Glass FIber - Low water uptake - High efficiency for particles > 0.3 μm - Resistant to high T Organics Cellulose - Low head loss - Low metallic contamination level - Easily ashed - Hydrophillic Metals + inorganic ions Membrane - Flat for microscopic analysis - Hydrophobic - Chemically resistant - Large head loss - Brittle - Not resistant high T

Chemical Composition Inorganic and organic –Elemental –Speciation - Compounds or ions

Metals Total metals via HF digestion (teflon beakers or microwave bomb digestion) If known composition use less severe dissolution method Analysis via FAAS, UV-Vis spectrometry, IC or or ICP methods

Speciation of Metals Requirements –Teflon or quartz filters (may have high blank values) –Clean room due to low levels –Filter storage and use of teflon tweezers for handling –Digested in HNO 3 –Analysis via ICP-MS for ng/m 3 concentrations

Organics Organic content may be measured in 2 ways –Analysis of Total Organic Carbon (TOC) –Weight loss after extraction with organic solvent Analysis via GC methods

Direct Analysis of Solids (Non-destructive) X-Ray Fluorescene –Irradiation of atoms with X-rays leads to e - ejection from inner shells –Cascading outer e - emit X-rays, λ of radiation emitted can be used to calculate atmoic no. –Elements emit radiation of characteristic λ –Intensity concentration Available as portable devices

Direct Analysis of Solids X-Ray Emission –Bombardment with fast e - –Used in electron microprobe analyzer –Can probe individual particles Neutron Activation Analysis –Sample is irradiated by neutrons to produce radionuclides of the elements of interest –Nuclides are detective via gamma emissions –Highly sensitive

Question What are some disadvantages of solid-state techniques over traditional dissolution methods? Material analyzed has to be representative of the whole sample Particuarly problematic with X-ray fluorescence since surface layers may have a different composition to the bulk Requires highly specialized spectrometers

Further Reading Journal articles

Text Books Hesketh, H.D. (1994) Air and Waste Management: A Laboratory/Field Handbook. CRC Press, Florida. Lodge, J.P.A. ed. (1988) Methods of Air Sampling and Analysis, 3rd Edition. CRC Press, Florida. Wight, G.D. (1994) Fundamentals of Air Sampling. CRC Press, Florida. Winegar, E.D. and Keith, L.A. eds. (1993) Sampling and Analysis of Airborne Pollutants. CRC Press, Florida.