New Particle Formation 

New particle formation (NPF) is a key atmospheric process that has profound effects on air quality, human health, and climate. We investigate NPF across urban, rural, and coastal environments, combining measurements of gas-phase nucleation precursors and aerosol-phase chemical composition to identify the chemical mechanisms driving particle formation and growth under diverse atmospheric conditions.

To complement our field observations, we conduct molecular-level laboratory kinetics studies of multicomponent NPF. Using controlled flow-tube experiments coupled with mass spectrometers and aerosol instruments, we investigate how naturally emitted chemical species (e.g., biogenic VOCs and marine tracers) and anthropogenic pollutants interact to influence particle formation.

Emerging Air Pollutants

PFAS are man-made “forever-chemicals” that have detrimental effects on human health and ecosystems. We investigate the occurrence, composition, and transformation of gas- and particle-phase PFAS in the urban atmosphere and wildfire smoke. Using high-resolution mass spectrometry, we characterize their molecular composition and structures to better understand their sources and atmospheric behavior.

Ammonia and amines are essential chemical precursors for aerosol formation, yet their measurement at atmospheric concentrations remains extremely challenging. We develop advanced analytical techniques to enable sensitive and rapid measurements of these compounds. Our chemical ionization mass spectrometer (CIMS) measures ambient ammonia and amines at ppt to sub-ppt levels with a response time of less than one minute—a capability available in only a few instruments worldwide.

Wildfire Smoke Chemistry

Wildfires are an increasingly important source of air pollution in the United States and worldwide. In collaboration with Dr. Rawad Saleh at the University of Georgia, as part of the GWISE campaign, we investigate the chemical evolution of air toxicants emitted from prescribed fires. Our research focuses on oxygenated organic compounds, reduced nitrogen compounds, and PFAS to understand their atmospheric transformation and fate in wildfire smoke.

Satellite Data Analysis of Air Quality

In collaboration with Dr. Can Li at NASA GSFC, we use satellite observations to investigate the spatial and temporal variability of air pollution. We analyze observations of SO₂, particulate matter, and wildfire smoke from polar-orbiting satellites such as TROPOMI and geostationary platforms such as TEMPO. By integrating satellite observations with in-situ measurements, GEOS-Chem modeling, and machine learning, we investigate the distribution, evolution, and drivers of air pollution from regional to continental scales.