Use of Nephelometry as a Long-term Measure of Particle Pollution
Fine particle pollution is an ongoing concern in urban airsheds, although measurement technologies and policies for PM2.5 have only recently been deployed in Australia. One possible surrogate for fine particle measurement is the nephelometer, which measures the amount of light scattered by particles and gases in an atmospheric sample.
EPA Victoria began sampling with nephelometers in 1979. Instruments were carefully maintained for over two decades before being replaced with newer equipment in 2003. A 22-month trial with old and new instruments in parallel showed an excellent correlation, which has allowed the instrument fleet to be replaced without loss of continuity in measurement.
Light scattering measurements were also found to correlate well with manual gravimetric PM2.5 data at several sites in Melbourne. This allows estimates of PM2.5 to be determined at low cost, although site-specific relationships would need to be developed, and periodically re-established to account for any trends in aerosol properties.
To manage particle pollution, we must be able to determine trends over time given advances in technology. This requires a detailed understanding of how instruments respond to particles with variable size distributions, amounts of moisture and semi-volatile matter. Although nephelometry as usually deployed does not quantify these variations, it does provide a simple and robust methodology that can be deployed over long time scales, giving an indication of the success or otherwise of air quality management programs.