Quantification of secondary particle loading during a heavy air pollution event in Beijing: A simplified method based on coal emission indicators

Secondary aerosol (SA) is considered to be an increasingly dangerous air pollutant. However, quantification of SA has suffered from considerable uncertainty due to its poorly understood formation mechanism. In this study, a simplified approach based on characterizing coal combustion emission indicators polonium-210 (Po-210), selenium (Se) and arsenic (As) was used to estimate SA loading (increment) during a heavy air pollution event in December 2016 in Beijing. Due to the insignificant input and output of air pollutants as well as the assumption of non-local emissions during this heavy air pollution event, a steady-state method of severe air pollution has been proposed to estimate SA increment (the sum of newly formed secondary inorganic aerosols and secondary organic aerosols) during this typical air pollution event. Corresponding algorithm of the method was developed depending on the characteristics of coal combustion related pollutants (210Po, Se, and As). The results indicated that the median contribution of newly formed SA to total suspended particulates (TSP) during this heavy air pollution event was 42.4% (interquartile range [IQR]: 36.6%-48.8%), which quantitatively confirms the dominant contribution of substantial enhancement of SA to heavy air pollution. Although further verification is needed, this steady-state method of evaluating severe air pollution has potential for quantification of the SA increment.