Rethinking primary particulate matter: Integrating filterable and condensable particulate matter in measurement and analysis

The current definition of primary particulate matter (PM) encompasses filterable PM (FPM) and condensable PM (CPM), which are evaluated using two distinct conventional measurement methods: cooling and dilution. While the cooling method exclusively considers the homogenous formation of CPM, the dilution method, closer to real-world conditions, neglects FPM characterization. To overcome this limitation, we propose a doubled-dilution system that enables the parallel characterization of both FPM and primary PM without diverting FPM from the CPM formation pathway. The doubled-dilution system has been investigated from a laboratory scale to a full-scale coal-fired power plant to facilitate simultaneous, real-time measurements of primary PM and FPM size distributions. Moreover, the formation rates of homogeneous and heterogeneous nucleation were compared. The evolution of the primary PM size revealed a bimodal distribution, and the filter-based mass concentration results demonstrated a pronounced preference for heterogeneous reactions (17.6 times higher than homogeneous nucleation). In particular, primary PM emissions were underestimated by up to 65.3 % when only homogeneous CPM formation was considered, underscoring the importance of including FPM during primary PM measurements. Considering these results, we advocate adopting the term “primary PM” over “CPM.”