Development of an ultrafine aerosol particle mobility analyzer with separation and sensitivity enhancement and real-time monitoring

The goal of this project is to develop a new instrument to measure accurately the size distribution of nanoparticles sampled in a variety of environmental applications. The new instrument will enhance the sensitivity, selectivity, and detection speed of ultrafine particles up to 100 nanometers in size, which are referred to as PM0.1 particles. Particles of this small size arise from the same natural or human-made sources that produce larger particles, but PM0.1 particles may pose special health threats because they readily enter the body.

Improved measurement techniques could help with the detection and control of PM0.1 particles in the environment. The instrument that will be developed is an Ion Mobility Spectrometer (IMS). The IMS will use an electric field that varies spatially to restrict diffusion of particles in the gas phase and therefore will enhance the resolution of measurements of the particle size distribution.

In addition, the IMS system will be coupled to a mass spectrometer so that particle mobility can be correlated with particle mass. The use of this new instrument will improve our fundamental understanding of aerosol and nanoparticle characterization and transport in the gas phase. The research team will conduct activities that demonstrate principles of aerosol science to K-12 students, especially those from underrepresented groups, in summer camps.

The team will also communicate the role of aerosols in climate change and pollution through K-12 teacher/mentor awareness symposia.

Aerosols are generally classified by size obtained from their mobility in the gas phase. Most often, mobility-based size distribution functions of aerosol particles are measured with a scanning mobility particle sizer (SMPS). While the SMPS has been highly successful, it has several shortcomings that could be addressed by employing different techniques.

For example, diffusional broadening leads to a degradation in resolution for most operating commercial devices. Furthermore, SMPSs typically require minutes to complete voltage scans. This duration limits the information that can be obtained when aerosol samples vary rapidly in time, which can occur when sampling near aircraft or roadways.

These challenges are exacerbated for measurements of PM0.1 particles in the gas phase. Despite continued experimental and theoretical interest, there is still a knowledge gap in the theoretical understanding of momentum transfer of particles that lie in the free molecular regime (1-100nm). The proposed research is expected to impact the aerosol field through increases in instrument separation/resolution by restricting diffusion broadening of nanoparticles, classifications of small aerosols through a mass-mobility and size relationship and quick, low signal-to-noise scans to study rapidly varying aerosols (up to tens of milliseconds per scan for particles smaller than 10 nanometers).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.