Alternative metrics for spatially and temporally resolved ambient particle monitoring

• Introduced theory and physical meaning of PS/PN ratio first time.
• Proposed metrics ideal for routine monitoring with high spatiotemporal resolution.
• Validated the proposed metrics using complementary particle size distributions

Particle active surface area is regarded as an important alternative metric to correlate particle emissions to adverse health effects. We explore the use of a particle counter and a diffusion charger as a relatively simple means to measure spatiotemporally resolved particle concentrations over a wide region using a mobile platform. Although the scanning mobility particle sizer (SMPS) measurements provide particle size distributions (PSDs) that can be converted into many important metrics, this method is impractical to implement for a routine monitoring over a wide region. In this study, an alternative method and new metrics are introduced using the condensation particle counter (CPC) and electrical aerosol detector (EAD). While the CPC and EAD measure particle number (PN) and particle active surface area (PS) concentrations respectively, the ratio of PS/PN provides an additional information of particle size which is important for particle transport. PSDs measured by SMPS during ambient monitoring were used to verify the concept. The study found that alternative metrics (PN, PS, and PS/PN) can be used to monitor spatiotemporally resolved particle concentrations over a wide region.