Advantages of using the Ecotech three wavelength nephelometer for aerosol measurements
The measurement of the scattering properties of aerosols is limited by the errors introduced by typical single wavelength integrating nephelometers. These limitations, however, can be reduced by implementing the features of the Ecotech Three Wavelength Integrating Nephelometer. These limitations are predominantly contributed by particle size, relative humidity, Lambertian distribution of the light source, truncation error and the wavelength of the nephelometer. Fitting a PM2.5 size selective inlet and controlling the relative humidity of the sample reduces the effects of larger particle sizes and moisture. The errors introduced by a non-Lambertian light source can be reduced by calibrating the light source distribution. This feature is unique to the Ecotech design. The truncation errors introduced by the physical constraints of the nephelometer’s measurement cell can also be corrected by measuring the sample at three distinct wavelengths (450nm, 520nm & 700nm). The Ecotech Three Wavelength Integrating Nephelometer also has the added advantage of a compact three wavelength light source, which eliminates the need for complex optics and multiple photomultiplier tubes, making the instrument more portable and robust. Theoretical studies have shown that the use of a size selective inlet can improve the uncertainty of the scattering measurement by an order of up to 30% at a particle size of < 1μm. Further studies have shown that correcting the truncation errors by measuring at different wavelengths can reduce this error a further 10%. These conclusions highlight that the Ecotech Three Wavelength Integrating Nephelometer can be used for very precise measurements of aerosol properties in varying conditions.