Development and Characterization of a Time-Sequenced Cascade Impactor: Application to Transient PM2.5 Pollution Events in Urbanized and Industrialized Environments

Soulemane Halif Ngagine,Fabien Marteel,Pierre Kulinski,Karine Deboudt,Pascal Flament,Marie Choël

doi:10.3390/atmos13020244

Abstract

To set up a sampling and analysis strategy for particulate matter (PM) based on the time periods used in international standards is often inadequate for assessing the impact of day/night cycles or episodic emissions on urban air quality. To obtain a detailed physico–chemical characterization of urban PM when concentrations exceed the regulatory thresholds, a new rotary cascade impactor named the Time-Resolved Atmospheric Particle Sampler (TRAPS) was designed and tested for coarse and fine particle sampling. The TRAPS implementation, coupled with Optical Particle Counter measurements, provides time-resolved samples that can be analyzed by a wide range of single-particle analysis techniques. The TRAPS theoretical design was verified experimentally. Experimental cut-off diameters of 1.32 and 0.13 µm, respectively, for coarse and fine stages, were found in good agreement with theoretical values. Additionally, good trace separation, preventing inter-sample contamination, was evidenced by Scanning Electron Microscopy (SEM). The homogeneous distribution of particles of different types over a trace was also verified. As a case study, automated SEM-EDX analysis of 2500 particles, collected during two pollution peaks of a transient PM2.5 pollution event, revealed that individual particles’ chemical composition was influenced by local sources during the first pollution peak, and mainly transported during the second peak.

Highlights

Air pollution has been identified as the greatest environmental cause of premature deaths, with seven million deaths per year worldwide due to the direct or indirect effects of exposure to air pollutants [1]
We present a case study in which the Time-Resolved Atmospheric Particle Sampler (TRAPS) is implemented at a multi-influenced site during a PM2.5 pollution event
The results obtained from the experiments indicate that the size segregation characteristics of the TRAPS are in good agreement with theoretical calculation, with cut-off diameters of 1.32 and 0.12 μm for coarse and fine particle fractions, respectively, considering silica particles

Summary

Introduction

Air pollution has been identified as the greatest environmental cause of premature deaths, with seven million deaths per year worldwide due to the direct or indirect effects of exposure to air pollutants [1] Among these pollutants, particulate matter (PM) has the greatest health impact [2], PM2.5 and PM1 because of their ability to penetrate the deeper regions of the respiratory tract [1,3,4,5]. Air quality has significantly been improved in high-income countries, PM2.5 exceedances are frequent in large European cities, and a disparity in exposure between highly industrialized/urbanized cities and rural areas is observed [1] This leads us to question the sources of these disparities and, in particular, those responsible for exceeding the regulatory thresholds, especially in urban areas. The difficulty related to the smaller number of particles collected in shorter sampling times (e.g., less than 1 h) can be overcome by using individual particle analysis techniques, such as SEM-EDX [8]

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Conclusion