Abstract
ABSTRACT The performance of particle size separators that are characterized by their cutpoint (d50) and the steepness of their penetration curves (σg) is a critical feature of measurement methods for ambient PM2.5 and PM1 monitoring. The parameters d50 and σg for PM2.5 size separators are regulated in the official measurement methods of many countries and regions. However, those parameters for PM1 size separators have not been previously specified. The interaction of particle size distributions (PSDs) and the particle size separator performance characteristics has significant influence on the PM sampling results. Atmospheric PSDs for each of the four seasons covering a range of particulate pollution concentrations were measured in urban Beijing. The relative differences (RD) between estimated PM2.5/PM1 sampler concentrations and actual concentrations associated with the interaction between performance characteristics of size separator and actually measured urban PSDs, as well as for three idealized ambient PSDs, have been systematically investigated. For the PM2.5 size separator, when tolerance of cutpoint is 2.5 ± 0.2 µm and σg is no greater than 1.3, RD values for most typical urban atmospheric aerosol conditions were within the permissible error range (± 5%). For the PM1 size separator, when tolerance of cutpoint and sharpness is 1.00 ± 0.02 µm and σg no greater than 1.2, respectively, the RD values for typical urban atmospheric aerosol conditions are within the permissible range. Those parameters could also meet the requirements for sampling of the idealized ambient aerosol distribution.
Highlights
PM2.5 has been promulgated as an indicator in ambient air quality standards (AAQS) of many countries and regions, such as the United State of America (USA), the European Union (EU), Japan, and China (Cao et al, 2013)
The performance of particle size separators that are characterized by their cutpoint (d50) and the steepness of their penetration curves is a critical feature of measurement methods for ambient PM2.5 and PM1 monitoring
The relative differences (RD) between estimated PM2.5/PM1 sampler concentrations and actual concentrations associated with the interaction between performance characteristics of size separator and measured urban particle size distributions (PSDs), as well as for three idealized ambient PSDs, have been systematically investigated
Summary
PM2.5 (particles with aerodynamic diameter < 2.5 micrometers [μm]) has been promulgated as an indicator in ambient air quality standards (AAQS) of many countries and regions, such as the United State of America (USA), the European Union (EU), Japan, and China (Cao et al, 2013). The regulatory limits on the ambient mass concentration on annual and daily average bases have been set. Factors influencing the accuracy of the measured results include ambient aerosol concentration and composition, particle size distribution (PSD), sample volumetric flow rate, sampling time, sampler. Among these factors, the performance of the particle size separator is a critical feature of the measurement method. The performance of the particle size separator is normally described by either a collection efficiency curve or penetration curve. The penetration curve is characterized by its cutpoint (d50) and the steepness of the selection curve (σg). The cutpoint is the particle aerodynamic diameter at which probability of penetration through the size separator is 50%. The steepness is equivalent to the geometric standard deviation of a cumulative lognormal curve fitted to the penetration data, and both are often interchanged (Kenny and Gussman, 2000; Peters et al, 2001)
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