White-light optical particle spectrometer for in situ measurements of condensational growth of aerosol particles

Morphology and hygroscopicity of nanoplastics in sea spray

The role of airborne nanoparticles in atmospheric chemistry and public health is largely controlled by particle size, morphology, surface composition, and coating. Aerosol mass spectrometry provides real-time chemical characterization of submicron atmospheric particles, but analysis of nanoplastics in complex aerosol mixtures such as sea spray is severely limited by challenges associated with separation and ionization of the aerosol matrix. Here we characterize the internal and external mixing state of synthetic sea spray aerosols spiked with 150 nm nanoplastics. Aerosols generated from pneumatic atomization and from a sea spray tank are compared. A humidified tandem differential mobility analyzer is used as a size and hygroscopicity filter, resulting in separation of nanoplastics from sea spray, and an inline high-resolution time-of-flight aerosol mass spectrometer is used to characterize particle composition and ionization efficiency. The separation technique amplified the detection limit of the airborne nanoplastics. A salt coating was found on the nanoplastics with coating thickness increasing exponentially with increasing bulk solution salinity, which was varied from 0 to 40 g kg-1. Relative ionization efficiencies of polystyrene and sea salt chloride were 0.19 and 0.36, respectively. The growth-factor derived hygroscopicity of sea salt was 1.4 at 75% relative humidity. These results underscore the importance of separating airborne nanoplastics from sea salt aerosol for detailed online characterization by aerosol mass spectrometry and characterization of salt coatings as a function of water composition. The surface coating of nanoplastic aerosols by salts can profoundly impact their surface chemistry, water uptake, and humidified particle size distributions in the atmosphere.

Approach for correcting particle size distribution measured by optical particle counter in high-pressure gas pipes

A set of online particle detection devices was developed for the quick and accurate assessment of particle size and concentration in high-pressure natural gas that can be applied at any pressure below 10 MPa. In actual site tests with P=3.42 and 2.36 MPa, the online tested results of particle size and concentration are generally smaller compared to those of the offline gathered under atmospheric conditions. That is mainly due to the detection performance degradation of an optical particle counter caused by gas pressure change leading to the refractive index change of the sounding medium with which the optical paths of the incident light and scattering light are altered. Aiming to solve this problem, an analysis of the dynamic change of optical measurement volume of the optical detection system with gas pressure was conducted based on the gas state parameters and geometric optics theory, and a dynamic model of both was established that can be accompanied by a particle size modification method based on light scattering theory. After a correction of tested results, the deviations in median diameter and concentration between the modified online and offline test results were within an acceptable range. Therefore, the proposed modification is a feasible and reliable approach to enhance online particle detection.