Field Methods of Monitoring Atmospheric Systems Measurement of Air Pollution Copyright © 2009 by DBS

Introduction Usually carried out at fixed site monitoring stations Routine monitoring is carried out primarily for the protection of public health

Methods of Analysis Can be broken down into two broad categories: (i) Chemical measurements – best suited for 24hr average concentrations or longer (ii) Procedures based on the physical properties of the pollutant – continuous fast-response measurements

Sulfur Dioxide (SO 2 ) Gas phase fluorescence instrument Air is drawn continuously through a cell in which it is irradiated by light (λ = 214 nm) Causes fluorescence, intensity of which is proportional to the SO 2 concentration Measures down to 1 ppb (~1 min)

Particulates Hi-Volume sampler has been used for many years Size selective impactor inlets allow collection of PM-10 and PM hr collection period

Particulates Hi-Vol has been replaced by tapered element oscillating microbalance (TEOM) Continuous measurements (~15 mins) in real-time Air is drawn through a PM-10 or 2.5 size selective inlet and heated to remove water vapor Dried particles are collected on a filter attached to the vibrating element of an oscillating microbalance

Carbon Monoxide (CO) Gas filter correlation infra-red Broad band IR passing alternately through 2 gas cells containing CO and N 2 as they rotate beneath the IR source on a spinning wheel The IR pulses then travel through the multipass sample cell Sample beam is produced when IR passes through N 2 cell Reference beam when IR passes through CO Difference in signal is the result of absorption by CO within the sample Measures ppm (~2 mins)

Nitrogen Oxides (NOx) Chemiluminescence analyzer Based on light emission from chemiluminescent reaction between nitric oxide (NO) in air sample with ozone generated by the instrument O 3 + NO  NO 2 * + O 2 Measures down to 1 ppb (~1 min) NO Mode: Air sample is passed directly to reaction chamber measuring NO NOx Mode: Air sample is passed over a catalyst, converts NO x to NO NO 2 is calculated as the difference

Volatile Organic Compounds (VOCs) Difficult and expensive – not very common Due to wide range of compounds and low concentrations Methods require pre-concentration using an absorbent Analyzed using gas chromatography

Volatile Organic Compounds Polyurethane Foam Sampler (PUF) For organics need both solid and vapor phases Vapor cartridge is placed in-line with quartz fiber filter for semi-volatile organics –PUF plug –Adsorbent resin (XAD-2) If vp is high VOC’s may be in aerosol form - Pesticides - PCB’s - Dioxins - PAH’s

Ozone (O 3 ) UV photometric analyzers – utilize absorption of UV by O 3 at 254 nm Measured in long path absorption cell through which air sample is drawn Air passes through a direct inlet and an inlet which passes through an ozone scrubber Difference in UV absorption between the two inlet routes is solely due to ozone (~1 min) Can also use chemiluminescence with ethylene

Instrument Deployment and Use Careful calibration and zeroing required on a weekly basis Quality assurance Massive volumes of data require data-logging

Location of Monitoring Stations Inlets need to be well exposed to air from all directions Should be in open areas not close to high buildings –Background locations –Hot spots Science center inlet

Monitoring Networks Instruments usually form part of a network Network design varies according to purpose

Further Reading Journal articles Lodge (1989) Dollard (1995) From: Harrison, R.M. (1999) Measurements of Concentrations of Air Pollutants, in: Holgate, S.T., Koren, H.S., Samet, J.M. and Maynard, R.L. (eds.), Air Pollution and Health. Academic Press, NY.

Text Books Finlayson-Pitts, B.J., and Pitts, J.N. (2000) Chemistry of the Lower Atmosphere: Theory, Experiments and Applications. Academic Press, San Diego. Harrison, R.M. (1999) Measurements of Concentrations of Air Pollutants, in: Holgate, S.T., Koren, H.S., Samet, J.M. and Maynard, R.L. (eds.), Air Pollution and Health. Academic Press, NY. Heard, D.E. (ed.) (2006) Analytical Techniques for Atmospheric Measurement. Blackwell Publishing. Hollas, J.M. (1996) Modern Spectroscopy. John Wiley & Sons Ltd., New York.