Real-time detection of vehicle-originated condensable particulate matter through thermodenuder integrated aerosol measurement method at tailpipes

Abstract

Condensable particulate matter (CPM) corresponds to primary particulate matter <2.5 mu m (PM2.5) obtained through the condensation of gaseous air pollutants caused by temperature drops in the atmosphere. The internal combustion of vehicle engines can produce CPM because of the condensable compounds in the exhaust gas. Conventional CPM measurement methods have been developed for coal-fired power plants with stable emissions through sampling and off-site analyses. They are therefore unsuitable for detecting the rapidly changing vehicleoriginated CPM. In addition, the current system for evaluating PM2.5 from vehicles, based on the particle measurement program (PMP) protocol, provides only the emission factors of total PM2.5 (and not CPM separately) at a fixed temperature (-25 degrees C) and dilution ratio (- x 35). This study reports, for the first time, the development of a real-time detection method for vehicle-originated CPM through a thermodenuder (TD) integrated with real-time aerosol instruments. This method was designed to reduce the loss of CPM due to condensation and diffusion while sampling the exhaust gas. It permits the investigation of the effects of dilution gas temperature (5-45 degrees C) and dilution ratio (up to x 30) on the formation of CPM. During the feasibility test of this method using a diesel vehicle (Euro-4), the real-time total particle number concentrations (PNs) matched well with those obtained by a PMP protocol-based evaluation system. Moreover, this method detected PNs concentrations ten times higher than the detection limit (4 x 106 particles/cm3) of the PMP-based system. The emission factors of the total PM2.5 with a bulk density (1 g/cm3) measured by this method also showed consistency with the results of the PMP protocol. The mass emission factor of CPM determined by deploying the TD was -14.57 mg/km (-63% contribution to the total PM2.5).