1174980 - PM2.5 Ambient Air Quality Standards: Time to Rethink Temporal Variability, Morphology and Consider Nanoparticles

PM2.5 air pollution is regulated using PM2.5 ambient air quality standards. The PM2.5 ambient air quality standards constitute a key tool for achieving continuous reductions of PM2.5 air pollution in jurisdictions around the world. However, the current PM2.5 standards differ from jurisdiction to jurisdiction in several key aspects. They account for temporal variability differently and do not consider the morphology, chemical composition and size distribution of PM2.5 particles, including the contribution of nanoparticles, also known as ultrafine particles.
In this study, we compared PM2.5 ambient air quality standards and pollution in Canada versus China. The weaker PM2.5 standard in China is often exceeded in Beijing, while the more stringent standard in Canada is routinely met in Montreal. We analyzed how accurately the 98th percentile (used in Canada) versus arithmetic mean (used in China) can reflect the actual PM2.5 ambient air pollution. The use of the arithmetic mean in the PM2.5 standards instead of high (e.g., 98th, 99th ) percentiles masks acute pollution peaks and permits higher pollution.
Back trajectory analysis was performed by using HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The analysis of the trajectories was performed in each season for all the observation locations. The PM2.5 concentration was affected by the origin of air masses and the boundary layer meteorology.
In a case study, we also analyzed the airborne particle size, shape, morphology, and elemental chemical composition of a sample of PM2.5 air pollution particles collected in Montreal. PM2.5 air pollution particles display highly varied morphology, a wide size distribution, including nanoparticles ( < 100 nm), and agglomerates of various compositions and sizes.
Recent and increasing evidence of adverse health effects associated with exposure to airborne nanoparticles should prompt consideration of particle-number-based PM2.5 standards. Regulatory agencies should consider particle morphology and chemical identity in the PM2.5 ambient air quality standards in light of the new evidence that particle size, morphology, and chemical identity affect translocation and effects of inhaled particles in the body.