Use of a multi wavelength integrating Nephelometer to determine Particle Mass Concentration and Size

摘要

Multi wavelength Nephelometry allows for the determination of the scattering Angstrom exponent. Since this factor is inversely related to particle size, it creates additional, useful and new possibilities in utilizing the measured data. The time series of the scattering coefficient represents the measured particle concentration and the corresponding Angstrom exponent shows information relative to the average (mode) diameter of the measured particle distribution. Not only is this information delivered near real time, it adds the ability of identifying different aerosol groups, or size fractions (as shown above), e.g. by capturing the coarse particle influence on a daily average measurement. Using this method would, for instance, allow a fixed measurement station to identify an influence of long-range transport of a special aerosol group not normally measured at that site. If the total PM measurement for this period exceeds the daily limiting values, the additional information provided by the nephelometer could allow regulatory agencies to deduct that event from the normal site annual average and daily average PM value, and could make the case that this "exceptional event" is outside the sites jurisdiction. For a routine monitoring application, a changing Angstrom exponent would indicate changes in the aerosol mix, site pattern could be generated by averaging the aerosol measurement over time and a significant deviation could be used to alert the user, e.g. by issuing a warning flag. With the stored measurement data, a detailed evaluation could subsequently be performed. With several stations utilizing this method, a geographical area could improve source apportionment studies as special aerosol characteristics of a given source could now be selectively be targeted.